Vitamin B and its derivatives for diabetic kidney disease

Abstract

Background

Diabetes is a leading cause of end‐stage kidney disease (ESKD) mainly due to development and progression of diabetic kidney disease (DKD). In absence of definitive treatments of DKD, small studies showed that vitamin B may help in delaying progression of DKD by inhibiting vascular inflammation and endothelial cell damage. Hence, it could be beneficial as a treatment option for DKD.

Objectives

To assess the benefits and harms of vitamin B and its derivatives in patients with DKD.

Search methods

We searched the Cochrane Renal Group's Specialised Register to 29 October 2012 through contact with the Trials' Search Co‐ordinator using search terms relevant to this review.

Selection criteria

We included randomised controlled trials comparing vitamin B or its derivatives, or both with placebo, no treatment or active treatment in patients with DKD. We excluded studies comparing vitamin B or its derivatives, or both among patients with pre‐existing ESKD.

Data collection and analysis

Two authors independently assessed study eligibility, risk of bias and extracted data. Results were reported as risk ratio (RR) or risk differences (RD) with 95% confidence intervals (CI) for dichotomous outcomes and mean difference (MD) with 95% CI for continuous outcomes. Statistical analyses were performed using the random‐effects model.

Main results

Nine studies compared 1354 participants randomised to either vitamin B or its derivatives with placebo or active control were identified. A total of 1102 participants were randomised to single vitamin B derivatives, placebo or active control in eight studies, and 252 participants randomised to multiple vitamin B derivatives or placebo. Monotherapy included different dose of pyridoxamine (four studies), benfotiamine (1), folic acid (1), thiamine (1), and vitamin B₁₂ (1) while combination therapy included folic acid, vitamin B₆, and vitamin B₁₂ in one study. Treatment duration ranged from two to 36 months. Selection bias was unclear in three studies and low in the remaining six studies. Two studies reported blinding of patient, caregiver and observer and were at low risk of performance and detection bias, two studies were at high risk bias, and five studies were unclear. Attrition bias was high in one study, unclear in one study and low in seven studies. Reporting bias was high in one study, unclear in one study, and low in the remaining seven studies. Four studies funded by pharmaceutical companies were judged to be at high risk bias, three were at low risk of bias, and two were unclear.

Only a single study reported a reduction in albuminuria with thiamine compared to placebo, while second study reported reduction in glomerular filtration rate (GFR) following use of combination therapy. No significant difference in the risk of all‐cause mortality with pyridoxamine or combination therapy was reported. None of the vitamin B derivatives used either alone or in combination improved kidney function: increased in creatinine clearance, improved the GFR; neither were effective in controlling blood pressure significantly compared to placebo or active control. One study reported a significant median reduction in urinary albumin excretion with thiamine treatment compared to placebo. No significant difference was found between vitamin B combination therapy and control group for serious adverse events, or one or more adverse event per patient. Vitamin B therapy was reported to well‐tolerated with mild side effects in studies with treatment duration of more than six months. Studies of less than six months duration did not explicitly report adverse events; they reported that the drugs were well‐tolerated without any serious drug related adverse events. None of the included studies reported cardiovascular death, progression from macroalbuminuria to ESKD, progression from microalbuminuria to macroalbuminuria, regression from microalbuminuria to normoalbuminuria, doubling of SCr, and quality of life. We were not able to perform subgroup or sensitivity analyses or assess publication bias due to insufficient data.

Authors' conclusions

There is an absence of evidence to recommend the use of vitamin B therapy alone or combination for delaying progression of DKD. Thiamine was found to be beneficial for reduction in albuminuria in a single study; however, there was lack of any improvement in kidney function or blood pressure following the use of vitamin B preparations used alone or in combination. These findings require further confirmation given the limitations of the small number and poor quality of the available studies.

Plain language summary

Vitamin B and its derivatives for diabetic kidney disease

Diabetic kidney disease (DKD) is a disorder which results in excessive protein, mainly albumin, loss in urine. DKD is a major cause of kidney failure and cardiovascular disease in patients with diabetes. Although vitamin B is commonly used in DKD, its effects are unclear. This review included nine studies with a total of 1354 participants. One study reported improvement in urinary albumin levels following use of thiamine. None of the other studies reported improvement in kidney function or reduction in urinary albumin excretion after two to 36 months monotherapy with vitamin B therapy. Vitamin B therapy was reported to well‐tolerated with mild side effects in studies with treatment duration of more than six months. Studies of less than six months duration did not explicitly report adverse events; they reported that the drugs were well‐tolerated without any serious drug related adverse events. All these findings require confirmation in larger studies before they can be accepted as definite.

Background

Description of the condition

Diabetic kidney disease (DKD) ‐ also known as diabetic nephropathy ‐ is a common complication that occurs in patients with both type 1 and type 2 diabetes mellitus (DM) (Marshall 2004; Mogensen 1995; Valk 2011). DKD is characterised by persistent positive albumin excretion in urine. The early stage of microalbuminuria is often referred as incipient nephropathy (urinary albumin excretion (UAE) > 30 mg/24 h) and can progress to macroalbuminuria (UAE > 300 mg/24 h) (overt kidney disease) in the absence of other kidney disease. Glomerular filtration rate (GFR) impairment and end‐stage kidney disease (ESKD) are markers of late stage DKD. Patients with DKD types 1 and 2 share similar prognostic patterns (Mogensen 1995; Mogensen 1999). DKD occurs in approximately 20% to 50% of patients with types 1 and 2 diabetes within 20 to 25 years of diabetes onset (Bloomgarden 2008; Dronavalli 2008; Gross 2005; Marshall 2004; Ritz 1999). Progression from microalbuminuria to macroalbuminuria occurs in 40% to 60% of patients with types 1 and 2 DM over 5 to 10 years of period (Bloomgarden 2008). Between 20% and 40% of patients with DKD progress to ESKD, and there is a high risk of death from associated coronary artery disease and other cardiovascular causes with DKD (Dinneen 1997; Gall 1993). The risk of cardiovascular disease increases progressively as albuminuria levels escalate and GFR decreases (Adler 2003; Miettinen 1996; Valmadrid 2000). Cardiovascular disease is a major cause of death in patients with ESKD (Levin 2003) and therefore imposes a substantial burden in terms of morbidity, and mortality. DKD management strategies should be directed towards limiting progression to ESKD and reducing mortality.

Risk factors associated with development of DKD include sustained hyperglycaemia and hypertension (Adler 2000; Fioretto 1998; Gall 1997; MCSG 1999; Ravid 1998; Stratton 2000); glomerular hyperfiltration (Caramori 1999; Dahlquist 2001; Silveiro 1998); smoking (Hovind 2003; Sawicki 1994); dyslipidaemia (Appel 2003; Chaturvedi 2001; Gall 1997; Ravid 1998); proteinuria levels (Ruggenenti 1998; Remuzzi 1997); and dietary factors, such as the amount and source of protein (Mollsten 2001; Pecis 1994; Toeller 1997) and fat (Riley 1998) in the diet as putative risk factors. Multidimensional management is therefore required for DKD to control risk factors and inhibit pathogenic pathways. Despite availability of effective therapies that can reduce progression of DKD, such as angiotensin‐converting enzyme inhibitors (ACEis), angiotensin receptor blockers (ARBs), prostaglandin E1, and aldosterone antagonists, many patients with DKD develop ESKD (Bolignano 2014; Wang 2010). Around 40% of the estimated 21 million patients with diabetes in the United States develop advanced DKD despite optimum treatment (Palmer 2008). More and newer interventions are required to limit the impact of DKD.

Description of the intervention

The B vitamins are a group of eight water‐soluble vitamins that play important roles in cell metabolism. Vitamin B complex contains all eight components: vitamin B₁ (thiamine), vitamin B₂ (riboflavin), vitamin B₃ (niacin or niacinamide), vitamin B₅ (pantothenic acid), vitamin B₆ (pyridoxine, pyridoxal, or pyridoxamine, or pyridoxine hydrochloride), vitamin B₇ (biotin), vitamin B₉ (folic acid) and vitamin B₁₂. Vitamin B₁₂ has several congeners: cyanocobalamin, hydroxocobalamin, methylcobalamin, and 5’‐deoxyadenosylcobalamin. Each vitamin B complex component has an individual structure and performs unique function in the human body. Vitamins B₁, B₂, B₃, and biotin participate in different aspects of energy production; vitamin B₆ is essential for amino acid metabolism, and vitamin B₁₂ and folic acid facilitate steps required for cell division. Thiamine is required for normal functioning of the heart, muscles, and nerves, and its intake is beneficial in the treatment of certain metabolic disorders (Malecka 2006; Thornalley 2005). Benfotiamine is a derivative of thiamine monophosphate which is better absorbed after oral administration than the water‐soluble thiamine salts resulting in higher levels of the active compound in blood and tissues (Schreeb 1997; Wu 2006). Requirements for components of the vitamin B complex vary considerably ‐ from 3 μg/d for vitamin B₁₂ to 18 mg/d for vitamin B₃ in adult males.

How the intervention might work

Hyperglycaemia is a major risk factor for DKD. It leads a cascade of biochemical reactions that are ultimately responsible for DKD. High cytosolic glucose concentration leads to metabolic dysfunction by over expression of glucose transporter‐1 (GLUT1) in renal mesangial cells. These involve activation of the protein kinase C (PKC) (Ayo 1991) hexosamine pathway, and polyol pathways (Chung 2003); accumulation of triose phosphates (Tilton 1992); metabolic pseudo hypoxia; mitochondrial dysfunction, oxidative stress (Nishikawa 2000; Yim 2001) and accumulation of advanced glycation end (AGE) products (Brownlee 2001; Du 2000; Heilig 1995). AGE products accumulate in the kidneys which are centrally involved in AGE product clearance (Forbes 2003). There is a strong correlation between AGE product accumulation and the presence and severity of DKD (Monnier 1999). High sugar level in cells disrupts normal cellular glucose metabolism resulting in accumulation of super reactive glucose‐metabolic intermediates such as triose phosphates. Excess triose phosphates attack surrounding proteins, lipids and DNA resulting in formation of oxo aldehydes that creates AGE product damage (Brownlee 2001; Thornalley 2005). Accumulation of triose phosphates arising from high cytosolic glucose concentrations trigger biochemical dysfunction in renal cells that ultimately leads to development of DKD (Babaei‐Jadidi 2003; Nishikawa 2000; Tilton 1992). Preventing triose phosphate accumulation in hyperglycaemia can suppress these pathways and prevent DKD development.

Thiamine has been associated with reducing serum and tissue accumulation of AGE products and investigated for its utility in DKD prevention (Thornalley 2005). Thiamine pyrophosphate (TPP), an active form of thiamine, has been shown to prevent AGE product formation by inhibiting conversion of Amadori products to AGE products (Booth 1996; Goh 2008). TPP normalises triose phosphates by activating the reductive pentose phosphate pathway (Babaei‐Jadidi 2003). TPP activates an enzyme (transketolase) that shunts excess triose phosphates into a safe alternative pentose phosphate metabolic pathway which prevents formation of AGE products and high sugar‐induced metabolic cellular stress (Goh 2008; Hatfield 2005; Huijberts 2008). This action stimulates conversion of GA3P and fructose‐6‐phosphate (F6P) to ribose‐5‐phosphate (R5P) (Babaei‐Jadidi 2003). In pre‐clinical experimental models, high‐dose thiamine and benfotiamine corrected delayed replication; activation of PKC; increased hexosamine and AGE product concentrations; and oxidative stress in capillary and aortal endothelial cells (Bergfeld 2001; La Selva 1996). Benfotiamine blocks three major biochemical pathways that are involved in chronic hyperglycaemia‐induced vascular damage: the hexosamine pathway, AGE formation pathway and diacylglycerol–PKC pathway (Hammes 2003). Benfotiamine has been reported to prevent progression of diabetic complications by increasing tissue levels of thiamine diphosphate and subsequently enhancing transketolase activity (Hammes 2003; Volvert 2008). Supplementation with benfotiamine in patients with DKD has been reported to be responsible for decreased incidence of albuminuria/proteinuria, AGE product accumulation and oxidative stress in renal cells (Bakker 1997; Karachalias 2003; Thornalley 2007). Overall, these actions decrease inflammatory and fibrotic responses to inhibit DKD progression (Bakker 1997; Karachalias 2003; Thornalley 2007). Apart from thiamine, experimental studies have confirmed that pyridoxamine is also a potent inhibitor of AGE product accumulation, and effective in reducing kidney injury in diabetes (Alderson 2003).

Why it is important to do this review

Evaluating the efficacy of vitamin B and its derivatives, alone or in combinations, for inhibiting progression of DKD and reducing mortality may provide additional options to current treatment pathways for patients with DKD. There is a substantial body of published clinical studies, and many ongoing investigations, in the intervention of interest. Currently, there are no health technology assessment reviews or systematic reviews assessing vitamin B or its derivatives, or both for DKD. The scope of the current review is to identify and aggregate good quality evidence on vitamin B or its derivatives, or both for DKD with the major focus on core clinical and patient‐related outcomes ‐ as these aspects are important contributors to the strength of recommendations for all therapies and also the use of vitamin B preparations in DKD.

Objectives

We assessed the benefits and harms of vitamin B and its derivatives in patients with DKD.

Methods

Criteria for considering studies for this review

Types of studies

All randomised controlled trials (RCTs) and quasi‐RCTs (RCTs in which allocation to treatment was obtained by alternation, use of alternate medical records, date of birth or other predictable methods) evaluating benefits and harms of vitamin B or its derivatives, or both in the patients with DKD.

Types of participants

Inclusion criteria

We included studies conducted in patients with type 1 and type 2 DKD. To consistently capture changes in classification and diagnostic criteria for DM over time, we included studies that assigned standard criteria that were valid at study outset (e.g. ADA 1999; ADA 2008; ADA 2010; Alberti 1998; WHO 1980; WHO 1985). Ideally, diagnostic criteria should have been described. Further, diagnostic criteria for DKD should be mentioned clearly and should adhere to diagnosis provided by the American Diabetes Association (ADA) (ADA 1999; ADA 2008; ADA 2010; KDOQI 2007) and other standard guideline. If necessary, we used authors' definition of DM and DKD. We planned to investigate diagnostic criteria used for diabetes and DKD in sensitivity analysis.

Exclusion criteria

We excluded studies in patients with kidney injury due to diseases other than diabetes, and types of diabetes other than type 1 or type 2 diabetes (i.e. gestational diabetes) or patients with final stage DKD or ESKD (GFR < 10 mL/min or requirement for renal replacement therapy).

Types of interventions

• Vitamin B, its derivative preparations, or both versus placebo

• Vitamin B, its derivative preparations, or both plus other drugs versus other drugs (ACEIs, ARBs, calcium channel blockers (CCBs))

• Vitamin B, its derivative preparations, or both versus other drugs (ACEIs, ARBs, CCBs).

Types of outcome measures

Primary outcomes

• All‐cause mortality

• Cardiovascular mortality.

Secondary outcomes

• Progression from macroalbuminuria to ESKD

• Progression from microalbuminuria to macroalbuminuria

• Regression from microalbuminuria to normoalbuminuria

• Kidney function measures (creatinine clearance (CrCl), GFR, doubling of serum creatinine (SCr), SCr, proteinuria, dialysis)

• Blood pressure (systolic (SBP); diastolic (DBP))

• Quality of life

• Adverse events.

Timing of outcome measurement

We assessed outcomes in the short‐term (≥ 12 weeks to < 18 weeks), medium‐term (≥ 18 weeks to < 52 weeks) and long‐term (≥ 52 weeks). Data from long term extension studies of RCTs was considered only if participants were maintained the same sequence allocation as in the initial feeder study.

Search methods for identification of studies

Electronic searches

We searched the Cochrane Renal Group's Specialised Register (to 29 October 2012) through contact with the Trials' Search Co‐ordinator using search terms relevant to this review. The Cochrane Renal Group’s Specialised Register contains studies identified from the following sources.

1. Quarterly searches of the Cochrane Central Register of Controlled Trials CENTRAL

2. Weekly searches of MEDLINE OVID SP

3. Handsearching of renal‐related journals and the proceedings of major renal conferences

4. Searching of the current year of EMBASE OVID SP

5. Weekly current awareness alerts for selected renal journals

6. Searches of the International Clinical Trials Register (ICTRP) Search Portal and ClinicalTrials.gov.

Studies contained in the Specialised Register are identified through search strategies for CENTRAL, MEDLINE, and EMBASE based on the scope of the Cochrane Renal Group. Details of these strategies as well as a list of handsearched journals, conference proceedings and current awareness alerts are available in the Specialised Register section of information about the Cochrane Renal Group.

See Appendix 1 for search terms used in strategies for this review.

Searching other resources

1. Reference lists of clinical practice guidelines, review articles and relevant studies.

2. Letters seeking information about unpublished or incomplete studies to investigators known to be involved in previous studies.

Data collection and analysis

Selection of studies

The search strategy as described was used to obtain titles and abstracts of studies with relevance to the review. The titles and abstracts were screened independently by two authors who discarded studies that were not applicable; however, studies and reviews that may include relevant data or information on studies were retained initially. The same two authors independently assessed retrieved abstracts, and if necessary the full text of these studies to determine if they satisfy the inclusion criteria. Interrater agreement for selection of potentially relevant studies was measured using the kappa statistic (Cohen 1960). Disagreements were resolved by consensus between authors. A third author arbitrated if consensus could not be achieved. An adapted PRISMA flowchart illustrated the study selection process (Liberati 2009).

Data extraction and management

Data extraction was carried out independently by two authors using standard data extraction forms. Studies reported in non‐English language journals were to be translated before assessment. Where more than one publication of one study existed, reports be grouped together and the publication with the most complete data was used in the analyses. When relevant outcomes were only published in earlier versions these data were used. Any discrepancies between published versions were to be highlighted.

Assessment of risk of bias in included studies

The following items were independently assessed by two authors using the risk of bias assessment tool (Higgins 2011) (see Appendix 2).

• Was there adequate sequence generation (selection bias)?

• Was allocation adequately concealed (selection bias)?

• Was knowledge of the allocated interventions adequately prevented during the study (detection bias)?

  • Participants and personnel

  • Outcome assessors

• Were incomplete outcome data adequately addressed (attrition bias)?

• Are reports of the study free of suggestion of selective outcome reporting (reporting bias)?

• Was the study apparently free of other problems that could put it at a risk of bias?

Measures of treatment effect

Results were expressed as risk ratio (RR) with 95% confidence intervals (CI) for dichotomous outcomes, such as death. Mean differences (MD) was calculated where continuous scales of measurement were used to assess the effects of treatment (blood pressure, CrCl, UAE, SCr, quality of life), or the standardised mean difference (SMD) if different scales were used. Time‐to‐event outcomes (such as time to development of macrovascular disease or ESKD) were to be expressed as hazard ratios (HR) with 95% CI. Adverse effects were tabulated and assessed with descriptive techniques, as they are likely to be different for the various agents used. Where possible, the RR with 95% CI was calculated for each adverse effect, either compared to no treatment or to another agent.

Unit of analysis issues

We took into account the level at which randomisation occurred, such as cross‐over studies, cluster‐randomised studies and multiple observations for the same outcome (Higgins 2011).

Dealing with missing data

We obtained relevant missing data from some of included the study authors upon sending e‐mail to them. We investigated attrition rates (drop‐outs, loss to follow‐up and withdrawals) and critically appraise missing data issues and imputation methods (such as last‐observation‐carried‐forward) (Higgins 2011).

Assessment of heterogeneity

Heterogeneity was analysed using a Chi² test on N‐1 degrees of freedom, with an alpha of 0.05 used for statistical significance and with the I² test (Higgins 2003). I² values of 25%, 50% and 75% correspond to low, medium and high levels of heterogeneity, respectively.

Assessment of reporting biases

There were insufficient studies to assess potential existence of study bias using funnel plot.

Data synthesis

Data were pooled using the random‐effects model but the fixed‐effect model was also used to ensure robustness of the model chosen and susceptibility to outliers.

Subgroup analysis and investigation of heterogeneity

Subgroup analysis was conducted to explore possible sources of heterogeneity, such as participants, interventions and study quality. Heterogeneity among participants may be related to age and renal pathology. Heterogeneity in treatments may be related to prior agents used and dose and duration of therapy. We planned to perform subgroup analyses as one of the primary outcome parameters demonstrated statistically significant differences between intervention groups.

Due to insufficient studies, we were not able to conduct subgroup analysis as planned for primary outcomes based on the following criteria.

• Ethnicity of participants

• Microalbuminuria or macroalbuminuria

• Participants with or without hypertension, dyslipidaemia, or abnormal blood glucose

• Treatment duration (< 6 months or ≥ 6 months)

• Different combinations of vitamin B derivatives

• Dose

• Use of ACEi or ARB or both

• Use of other antihypertensive treatments.

Sensitivity analysis

Due to insufficient studies, we were not able to perform sensitivity analysis as planned to explore the influence of the following factors on effect size.

• Repeating the analysis excluding unpublished studies

• Repeating the analysis taking into account risk of bias, as specified

• Repeating the analysis excluding very long or large studies to establish how much they dominate the results

• Repeating the analysis excluding studies to filter: diagnostic criteria, language of publication, source of funding (industry versus other), and country.

Results

Description of studies

Results of the search

See Characteristics of included studies and Characteristics of excluded studies for full details of the studies.

We identified a total of 91 records (60 studies) after running the search strategy in Cochrane Renal Group's Specialised Register through contact with the Trials' Search Co‐ordinator. The search resulted in a unique list of references in which studies with multiple publications were linked through a common identifier.

We excluded a total of 50 studies (76 articles) based on titles or abstracts which were not relevant to our review. We included nine studies (14 records) for this review (Figure 1). There was a complete agreement in study selection process between the two authors.

1.

Study flow diagram.

One study, listed in ClinicalTrials.gov, is awaiting assessment (Characteristics of studies awaiting classification). This study evaluated the effects of folic acid in patients with DKD. We found neither a full publication nor any conference abstracts for this study. We were unable to get any data upon contacting the authors, we will incorporate this study as and when results are publicly available.

Included studies

We included nine studies enrolling 1354 participants (Agha 2009; Alkhalaf 2010; DIVINe Study 2010; Lewis 2012; PYR‐205 Study 2007; PYR‐206 Study 2007; PYR‐207 Study 2007; Rabbani 2009; Wotherspoon 2008). All were published in English and all were parallel group designs.

Number of study centres, countries, locations and settings

Four studies were carried out in a single centre at a diabetic outpatient clinic; two in Pakistan (Agha 2009; Rabbani 2009), one in the Netherlands (Alkhalaf 2010), and one in UK (Wotherspoon 2008). Five were multicentre studies. DIVINe Study 2010 was carried out at five different university medical centres in Canada. Four studies (Lewis 2012; PYR‐205 Study 2007; PYR‐206 Study 2007; PYR‐207 Study 2007) were international studies carried out in Australia, Canada, Belgium, Israel, South Africa, UK, and USA.

Duration of intervention

Duration of intervention varied from two months (Wotherspoon 2008), three months (Alkhalaf 2010; Rabbani 2009), six months (Agha 2009; PYR‐205 Study 2007; PYR‐206 Study 2007; PYR‐207 Study 2007); 12 months (Lewis 2012), and 36 months (DIVINe Study 2010).

Participants

Nine studies compared 1354 participants randomised to either vitamin B and its derivatives or placebo or active control. A total of 1102 participants were randomised to single vitamin B derivatives, placebo or active control in eight studies, and 252 participants randomised to multiple vitamin B derivatives or placebo.

Inclusion criteria

All the studies included patients with DKD, however, the diagnostic criteria and severity of DKD varied across the studies. Three studies (Agha 2009; Alkhalaf 2010; Rabbani 2009) included patients with initial stages of DKD. Alkhalaf 2010 included patients with UAE ranging from 15 to 300 mg/24 h or equivalent albumin:creatinine ratio (ACR) (males: 1.25 to 25 mg/mmol; females: 1.75 to 35 mg/mmol) in two of three samples despite ACEIs or ARBs, or both in unchanged dose for at least three months. Rabbani 2009 and Agha 2009 defined microalbuminuria as UAE 30 to 299 mg/24 h urine. Five studies (DIVINe Study 2010; Lewis 2012; PYR‐205 Study 2007; PYR‐206 Study 2007; PYR‐207 Study 2007) included advanced stages of DKD. Four studies (DIVINe Study 2010; PYR‐205 Study 2007; PYR‐206 Study 2007; PYR‐207 Study 2007) defined DKD as clinical or histological diagnosis of DKD, and UAE at least of 300 mg/d or urinary protein level of at least 500 mg/24 h; Lewis 2012 defined DKD as a SCR of 1.3 to 3.3 mg/dL (women) or 1.5 to 3.5 mg/dL (men), and 24 hour urine ACR ratio > 1200 mg/g while receiving an ACEis or ARBs at the maximum Food and Drug Administration recommended dosage for more than three months. Two studies included participants as per levels of their SCr ≤ 2.0 mg/dL (PYR‐205 Study 2007; PYR‐206 Study 2007) and 2.1 to 3.5 mg/dL in PYR‐207 Study 2007. Wotherspoon 2008 defined DKD as an ACR > 2.5 mg/mmol in men and > 3.5 mg/mmol in women in a minimum of two of three early morning urine samples taken on separate days over a period of three months.

Three studies (Agha 2009; Alkhalaf 2010; Lewis 2012) mentioned inclusion of only type 2 diabetes patients, four studies (DIVINe Study 2010; PYR‐205 Study 2007; PYR‐206 Study 2007; PYR‐207 Study 2007) included both type 1 and type 2 diabetes patients, and Wotherspoon 2008 included only patients with type 1 diabetes.

Exclusion criteria

Exclusion criteria among the included studies consisted of followings: significant diseases such as advance stage of kidney disease like ESKD; patients on dialysis or imminently expected to require dialysis; kidney insufficiency; kidney impairment by causes other than diabetes; other known kidney disease that may impact on progression rate such as renal artery stenosis or glomerular kidney disease such as membranous nephropathy; liver or kidney disorders; pregnant or lactating women; women of childbearing potential unwilling to practice a form of birth control for the duration of the study, in all of the included studies. Two studies (Alkhalaf 2010; DIVINe Study 2010) also excluded patients with cancer and another two studies (Alkhalaf 2010; Rabbani 2009) excluded patients with hypersensitivity to thiamine.

Co‐morbidities and co‐medications

Five studies (Alkhalaf 2010; Lewis 2012; PYR‐205 Study 2007; PYR‐206 Study 2007; PYR‐207 Study 2007) included patients with stable doses of ACEi or ARB or both in an unchanged dose for at least three months with DKD. In addition, DIVINe Study 2010 mentioned the use of antihypertensives, antiplatelets, antihyperglycaemic drugs in baseline as co‐medications. Rabbani 2009 also mentioned use of insulin, hypoglycaemic agents (sulphonylureas, metformin, thiazolidinedione), antihypertensive drugs, cholesterol lowering drugs among the participants.

Interventions and comparisons

Eight studies (Agha 2009; Alkhalaf 2010; Lewis 2012; Rabbani 2009; PYR‐205 Study 2007; PYR‐206 Study 2007; PYR‐207 Study 2007; Wotherspoon 2008) compared monotherapy of vitamin B preparations with placebo or active control. All interventions and controls were given orally.

• Benfotiamine: 900 mg/d (300 mg three times/d) versus placebo (once daily) (Alkhalaf 2010)

• Folic acid: 5 mg (once daily) versus placebo (Wotherspoon 2008)

• Pyridoxamine: 100 mg/d (50 mg twice daily) versus placebo (PYR‐206 Study 2007).

• Pyridoxamine: 300 mg/d, (150 mg twice daily) versus placebo (Lewis 2012)

• Pyridoxamine: 500 mg/d (250 mg twice daily) versus placebo in two clinical studies (PYR‐205 Study 2007; PYR‐207 Study 2007)

• Pyridoxamine: 600 mg/d (300 mg twice daily) versus placebo (twice daily) (Lewis 2012)

• Thiamine: 300 mg/d, (three 100 mg capsules of thiamine) versus placebo (once daily) (Rabbani 2009)

• Vitamin B₁₂: 500 µg/d (once daily) versus losartan 50 mg/d (once daily) (Agha 2009)

One study compared oral combined vitamin B therapy with placebo

• Vitamin B tablets containing 2.5 mg of folic acid, 25 mg of vitamin B₆, and 1 mg vitamin B₁₂ (once daily) versus matching placebo (DIVINe Study 2010)

None of the studies disclosed the contents of the placebo.

Reported outcomes

Three studies (Agha 2009; Alkhalaf 2010; Rabbani 2009) measured change from baseline in UAE as a primary outcome while DIVINe Study 2010 considered it under secondary outcomes. Change from baseline in SCr was a primary outcome in four studies (Lewis 2012; PYR‐205 Study 2007; PYR‐206 Study 2007; PYR‐207 Study 2007). In addition, Alkhalaf 2010 also measured Kidney Injury Molecule‐1 as a primary outcome. Secondary outcomes in Alkhalaf 2010 were change in urinary excretion of B₂ microglobulin, macrophage inhibiting factors, and other AGE products. DIVINe Study 2010 assessed kidney outcomes such as CrCl and progression to dialysis; vascular events such as stroke and death, and decline in cognitive function. Rabbani 2009 measured plasma cholesterol profile as a secondary outcome. None of the studies reported quality of life or cost as outcomes. Wotherspoon 2008 assessed plasma homocysteine, forearm blood flow, total antioxidant status, and whole blood glutathione.

Baseline characteristics

All the studies reported basic demographic, biochemical and clinical parameters compared at baseline. The number of patients ranged from 40 to 361 patients. Six studies (Alkhalaf 2010; DIVINe Study 2010; Lewis 2012; PYR‐205 Study 2007; PYR‐206 Study 2007; PYR‐207 Study 2007) had higher proportion of male participants compared to female, while Agha 2009 and Rabbani 2009 had roughly equal proportions of male and female participants. DIVINe Study 2010 included the patients with median duration of microalbuminuria of two years (interquartile range (IQR) = 3 years), while Lewis 2012 included the patients with mean duration of DKD of approximately five years. DIVINe Study 2010 had the highest UAE (maximum median 900 (IQR = 150) mg/24 h) in control group. Three studies (Agha 2009; Alkhalaf 2010; Rabbani 2009) included significantly higher proportion of patients with microalbuminuria.

Excluded studies

We excluded a total of 45 RCTs that did not assess the intervention in the population of our interest for the review. These studies included participants with established ESKD. Four studies were not randomised, and one study (Spoelstra 2004) was excluded as it assessed the effects of folic acid in patients with diabetes not having DKD.

Risk of bias in included studies

See Figure 2 and Figure 3.

2.

Risk of bias graph: review authors' judgements about each risk of bias item presented as percentages across all included studies.

3.

Risk of bias summary: review authors' judgements about each risk of bias item for each included study.

Interrater agreement for the key quality indicators such as randomisation, concealment of allocation and blinding was complete with no full publication needing to be discussed with a third author.

Allocation

Six studies (DIVINe Study 2010; Lewis 2012; Rabbani 2009; PYR‐205 Study 2007; PYR‐206 Study 2007; PYR‐207 Study 2007) were at low risk of selection bias related to random sequence generation and allocation concealment as participant allocation was conducted remotely or used sealed opaque envelopes. Three studies (Agha 2009; Alkhalaf 2010; Wotherspoon 2008) were unclear with respect to the risk of selection bias related to sequence generation and allocation, as the methods used were not clearly described.

Blinding

Agha 2009 was single blind study with high risk of detection or performance bias while other included studies were double blind studies. DIVINe Study 2010, Lewis 2012; and Rabbani 2009 were at low risk for performance bias provided the blinding condition at patient, caregiver and observer level with blinding of serum vitamin level in follow‐up. DIVINe Study 2010 was at low risk of performance and detection bias while five studies (Alkhalaf 2010; PYR‐205 Study 2007; PYR‐206 Study 2007; PYR‐207 Study 2007; Wotherspoon 2008) were judged as having unclear risk for performance bias and detection bias related to blinding, as the method used was not clearly described and did not report checking of blinding conditions. It was not confirmed whether any precaution was taken for blinding lab data of vitamin status (thiamine level) in the follow‐up and endpoint evaluation in those published clinical study reports.

Incomplete outcome data

DIVINe Study 2010 had a high risk of attrition bias. For clinical outcomes such as mortality, intention‐to‐treat analysis with 94% of randomised participant was utilised. A total of 87%, 81%, 68% and 47% of randomised participants were available for assessing biochemical outcomes at the end of 12, 18, 24 and 36 months respectively. DIVINe Study 2010 used multiple imputation techniques for missing variables. There was insufficient information available for Wotherspoon 2008 (unclear risk of bias) and all other studies were judged to be at low risk of bias.

Selective reporting

Seven studies had low risk of reporting bias based on comparison of reported outcomes in the protocol and final publication. The protocols were not available for two studies (Agha 2009; Wotherspoon 2008).

Publication and small study bias

No clear interpretation of the funnel plot was possible because of relatively small number of included studies.

Other potential sources of bias

Four studies funded by pharmaceutical companies were judged to be at high risk bias, three were at low risk of bias, and two were unclear.

Effects of interventions

We presented summary of results for reported outcomes of the available studies. Wotherspoon 2008 did not assess any of the outcomes prespecified in review.

Vitamin B versus placebo

Seven studies (Agha 2009; Alkhalaf 2010; Lewis 2012; PYR‐205 Study 2007; PYR‐206 Study 2007; PYR‐207 Study 2007; Rabbani 2009) compared monotherapy versus placebo or active treatment. Three studies (PYR‐205 Study 2007; PYR‐206 Study 2007; PYR‐207 Study 2007) presented the results of those studies in a single publication with combining data from two phase studies and a separate abstract for one study. The authors combined the data from individual studies to increase the sample size.

Primary outcomes

All‐cause mortality

Five studies reported all‐cause mortality (DIVINe Study 2010; Lewis 2012; PYR‐205 Study 2007; PYR‐206 Study 2007; PYR‐207 Study 2007)

Four studies (Lewis 2012; PYR‐205 Study 2007; PYR‐206 Study 2007; PYR‐207 Study 2007) reported all‐cause mortality with different doses of pyridoxamine monotherapy. There was no significant difference in risk of mortality with use of any dose or duration of pyridoxamine compared to placebo (Analysis 1.1) (100 mg/d for 6 months (1 study, 128 participants): RR 2.91, 95% CI 012 to 70.10; 300 mg/d for 12 months (1 study, 202 participants): RR 2.60, 95% CI 0.522 to 13.10; 500 mg/d for 5 months (1 study, 84 participants): RR 3.38, 95% CI 0.18 to 63.2; 600 mg/d for 12 months (1 study, 208 participants): RR 0.49, 95% CI 0.05 to 5.33).

1.1. Analysis.

Comparison 1 Vitamin B versus placebo, Outcome 1 All‐cause mortality.

DIVINe Study 2010 reported no significant difference in all‐cause mortality with the use of combined therapy versus placebo for three years (1 study; 238 participants: RR 0.86, 95% CI 0.30 to 2.48).

Cardiovascular mortality

No study reported cardiovascular mortality.

Secondary outcomes

Creatinine clearance

Six studies (Alkhalaf 2010; DIVINe Study 2010; Lewis 2012; PYR‐205 Study 2007; PYR‐206 Study 2007; PYR‐207 Study 2007) measured CrCl, however data were only available from Alkhalaf 2010.

Alkhalaf 2010 reported no significant difference in CrCl at the end of three months between benfotiamine and placebo (Analysis 1.2 (1 study, 82 participants): MD 2.00 mL/min, 95% CI ‐21.78 to 25.78).

1.2. Analysis.

Comparison 1 Vitamin B versus placebo, Outcome 2 Creatinine clearance.

Four studies (Lewis 2012; PYR‐205 Study 2007; PYR‐206 Study 2007; PYR‐207 Study 2007) reported no significant effects of pyridoxamine on improving CrCl compared to placebo.

DIVINe Study 2010 reported no significant difference in CrCl with combined vitamin B therapy compared to placebo.

Serum creatinine

Seven studies measured SCr (Alkhalaf 2010; DIVINe Study 2010; Lewis 2012; PYR‐205 Study 2007; PYR‐206 Study 2007; PYR‐207 Study 2007; Rabbani 2009), however DIVINe Study 2010 and Rabbani 2009 did not report their results.

Alkhalaf 2010 reported no difference in SCr following three months of benfotiamine compared to placebo (Analysis 1.3.1 (82 participants): MD 1.00 µmol/L, 95% CI ‐7.88 to 9.88). Lewis 2012 reported no significant change in SCr with either 300 mg/d (Analysis 1.3.2 (150 participants): MD 5.33 µmol/L, 95% CI ‐6.02 to 16.68) or 600 mg (Analysis 1.3.3 (157 participants): MD 0.02 µmol/L, 95% CI ‐11.05 to 11.09) pyridoxamine for 12 months. PYR‐205 Study 2007, PYR‐206 Study 2007 and PYR‐207 Study 2007 did not find any significant change in the SCr in the pooled estimate from all their studies (Analysis 1.3.4 (212 participants): MD ‐8.84 µmol/L, 95% CI ‐20.21 to 2.53).

1.3. Analysis.

Comparison 1 Vitamin B versus placebo, Outcome 3 Serum creatinine.

Proteinuria

Five studies (DIVINe Study 2010; Lewis 2012; PYR‐205 Study 2007; PYR‐206 Study 2007; PYR‐207 Study 2007) measured proteinuria, however, only two studies provided data (DIVINe Study 2010; Lewis 2012).

DIVINe Study 2010 reported no significant difference in the level of proteinuria after three years of combined vitamin B therapy compared to placebo (Analysis 1.4.1 (118 participants): MD: 0.05 g/24 h, 95% CI ‐0.39 to 0.49). Lewis 2012 reported no significant difference in proteinuria with pyridoxamine 300 mg/d (Analysis 1.4.2 (202 participants): MD ‐0.00 g/24 h, 95% CI ‐0.04 to 0.05); however there was a significant decrease in proteinuria in the 600 mg/d pyridoxamine group compared to placebo (Analysis 1.4.3 (208 participants): MD: ‐0.30 g/dL, 95% CI ‐0.34 to 0.25).

1.4. Analysis.

Comparison 1 Vitamin B versus placebo, Outcome 4 Proteinuria.

Urinary albumin excretion

Seven studies (Alkhalaf 2010; DIVINe Study 2010; Lewis 2012; PYR‐205 Study 2007; PYR‐206 Study 2007; PYR‐207 Study 2007; Rabbani 2009) measured UAE. None of the studies reported the data that could be meta‐analysed.

Rabbani 2009 reported a significant median reduction in UAE with thiamine treatment compared to placebo. The remaining studies did not find a significant reduction in UAE with either pyridoxamine, benfotiamine, or combined vitamin B therapy.

Glomerular filtration rate

Seven studies measured GFR (Alkhalaf 2010; DIVINe Study 2010; Lewis 2012; PYR‐205 Study 2007; PYR‐206 Study 2007; PYR‐207 Study 2007; Rabbani 2009), however Alkhalaf 2010, PYR‐205 Study 2007, PYR‐206 Study 2007 and PYR‐207 Study 2007 did not report their results.

DIVINe Study 2010 reported a significant reduction in GFR with combined vitamin B therapy compared to placebo (Analysis 1.5.1: MD ‐5.80 mL/min/1.73 m², 95% CI ‐10.51 to ‐1.10). Lewis 2012 reported no significant change in GFR with pyridoxamine (MD 0.36 mL/min/1.73 m², 95% CI ‐5.25 to 5.97), and Rabbani 2009 found no significant change in GFR with thiamine (MD 0.31 mL/min, 95% CI ‐4.51 to 5.13) when compared to placebo.

1.5. Analysis.

Comparison 1 Vitamin B versus placebo, Outcome 5 GFR.

Number of patients required dialysis

DIVINe Study 2010 reported no significant change in the risk of dialysis requirement with combined vitamin B therapy (Analysis 1.6 (238 participants): RR 1.00, 95% CI 0.43 to 2.31) compared to placebo.

1.6. Analysis.

Comparison 1 Vitamin B versus placebo, Outcome 6 Patients requiring dialysis.

Blood pressure

Six studies (Alkhalaf 2010; DIVINe Study 2010; PYR‐205 Study 2007; PYR‐206 Study 2007; PYR‐207 Study 2007; Rabbani 2009) measured blood pressure as an outcome, however data were not presented for three studies (PYR‐205 Study 2007; PYR‐206 Study 2007; PYR‐207 Study 2007).

Alkhalaf 2010 reported no significant difference SBP after 12 weeks of treatment with benfotiamine (Analysis 1.7.1 (82 participants): MD 3.00 mm Hg, 95% CI ‐4.37 to 10.37). DIVINe Study 2010 reported no significant change in the SBP with combined vitamin B therapy for 36 months (Analysis 1.7.2 (118 participants): MD 2.30 mm Hg, 95% CI ‐3.70 to 8.30) compared to placebo. Rabbani 2009 reported no change in SBP with thiamine given for 12 weeks (Analysis 1.7.3 (40 participants): MD 3.00 mm Hg, 95% CI ‐8.50 to 14.50) compared to placebo.

1.7. Analysis.

Comparison 1 Vitamin B versus placebo, Outcome 7 Systolic blood pressure.

Alkhalaf 2010 reported no significant change in DBP after 12 weeks of treatment with benfotiamine (Analysis 1.8.1 (82 participants): MD: 0.00, 95% CI ‐4.11 to 4.11). DIVINe Study 2010 reported no significant change in the DBP with combined vitamin B therapy for 36 months (Analysis 1.8 (118 participants): MD 1.50, 95% CI ‐1.60 to 4.60) compared to placebo. Rabbani 2009 reported no change in DBP with thiamine for 12 weeks (Analysis 1.8.3 (40 participants): MD 1.00, 95% CI ‐4.28 to 6.28).

1.8. Analysis.

Comparison 1 Vitamin B versus placebo, Outcome 8 Diastolic blood pressure.

Adverse events

Studies of less than six months duration did not explicitly report adverse events. They all reported that the drugs were well‐tolerated without any serious drug related adverse events.

Five studies (DIVINe Study 2010; Lewis 2012; PYR‐205 Study 2007; PYR‐206 Study 2007; PYR‐207 Study 2007) reported the adverse event profile in detail. DIVINe Study 2010 reported a total of 1060 adverse events (535 in the placebo group and 525 in the B vitamin group); these included many transient minor complaints, such as dizziness, nausea, or headache. Lewis 2012 reported 49 (46.7%) severe adverse events in the placebo group, 41 (39.4%) occurred in the pyridoxamine 150 group, and 42 (40%) occurred in the pyridoxamine 300 mg group. Data for two separate studies of pyridoxamine 500 mg/d and placebo were combined and compared by the authors (PYR‐205 Study 2007; PYR‐207 Study 2007); we combined the 300 mg/d and 600 mg/d data from Lewis 2012. No study reported significant differences in adverse events or in any serious or severe adverse events between vitamin B treatments and placebo (Analysis 1.9).

1.9. Analysis.

Comparison 1 Vitamin B versus placebo, Outcome 9 One or more adverse events per patient.

Vitamin B versus other substances

Agha 2009 compared Vitamin B₁₂ (mecobalamin) versus losartan (ARB; active control).

Primary outcomes

All‐cause mortality and cardiovascular morality were not reported.

Secondary outcomes

Serum creatinine

Agha 2009 reported no significant difference in SCr levels between the vitamin B₁₂ and losartan groups (Analysis 2.1 (261 participants): MD 0.00 mg/dL, 95% CI ‐0.09 to 0.09).

2.1. Analysis.

Comparison 2 Vitamin B versus active control, Outcome 1 Serum creatinine.

Urinary albumin excretion

Agha 2009 reported no significant difference in UAE levels between the vitamin B₁₂ and losartan groups (Analysis 2.2 (261 participants): MD 56.40 mg/dL, 95% CI 52.61 to 60.19).

2.2. Analysis.

Comparison 2 Vitamin B versus active control, Outcome 2 UAE.

Blood pressure

Agha 2009 reported a significant increase in SBP in the vitamin B₁₂ group (Analysis 2.3 (261 participants): MD 3.00 mm Hg, 95% CI 0.63 to 5.37).

2.3. Analysis.

Comparison 2 Vitamin B versus active control, Outcome 3 Systolic blood pressure.

Agha 2009 reported a significant increase in DBP in the vitamin B₁₂ group (Analysis 2.4 (261 participants): MD 2.70 mm Hg, 95% CI 0.29 to 5.11).

2.4. Analysis.

Comparison 2 Vitamin B versus active control, Outcome 4 Diastolic blood pressure.

Other outcomes

None of the included studies reported the following outcomes: progression from macroalbuminuria to ESKD, progression from microalbuminuria to macroalbuminuria, regression from microalbuminuria to normoalbuminuria, doubling of SCr, and quality of life. We were not able to perform subgroup or sensitivity analyses or assess publication bias due to insufficient data.

Discussion

Summary of main results

The review aimed to assess the effects of vitamin B therapy on various clinical and biochemical outcomes in patients with DKD. Nine studies (2560 participants) meet our inclusion criteria. Eight studies (Agha 2009; Alkhalaf 2010; Lewis 2012; PYR‐205 Study 2007; PYR‐206 Study 2007; PYR‐207 Study 2007; Rabbani 2009) assessed vitamin B or its derivatives versus placebo in patients with DKD (benfotiamine (300 mg/d), thiamine (300 mg/d), vitamin B₁₂ (500 mg/d), pyridoxamine (100 mg/d, 300 mg/d, 600 mg/d), folic acid (5 mg/d)); one study (Agha 2009) compared vitamin B with an active control (vitamin B₁₂ versus losartan); and one study (DIVINe Study 2010) compared combined vitamin B therapy (folic acid: 2.5 mg; vitamin B₆: 25 mg; vitamin B₁₂: 1 mg) with placebo. Treatment duration ranged from two to 36 months.

We found that there was no difference in the risk of all‐cause of mortality with pyridoxamine at doses of 100 mg/d, 300 mg/d, 500 mg/d, or 600 mg/d dose for five to 12 months of treatment compared to placebo (PYR‐205 Study 2007; PYR‐206 Study 2007; PYR‐207 Study 2007). None of the derivatives improved kidney functions such as increase in CrCl or GFR. Only one study reported improvement in UAE with thiamine (Rabbani 2009). None of the included studies reported outcomes such cardiovascular mortality, progression from macroalbuminuria to ESKD, progression from microalbuminuria to macroalbuminuria, regression from microalbuminuria to normoalbuminuria, number of patients requiring dialysis, quality of life parameters and cost.

DIVINe Study 2010 reported no significant difference in the risk of mortality with combined vitamin B therapy; conversely, the authors reported an increase in risk of MI, stroke, revascularization, and all‐cause mortality, in the B vitamin group after adjusting for baseline risk factors including peripheral vascular disease. Further, DIVINe Study 2010 reported a reduction in GFR following the use of vitamin B therapy. The combined vitamin B therapy neither significantly increased CrCl nor decreased the level of UAE. In addition, there were no additional benefits in reducing the risk of dialysis requirement with the combined vitamin B therapy. There was no significant difference between combined vitamin B group and placebo for adverse events. DIVINe Study 2010 did not report outcomes such as progression from macroalbuminuria to ESKD, progression from microalbuminuria to macroalbuminuria, regression from microalbuminuria to normoalbuminuria, CrCl, doubling of SCr, SCr, SBP, DBP, quality of life, and cost.

Overall completeness and applicability of evidence

The number of patients per study ranged from 16 to 361 and the age range was 40 to 75 years. We found different populations across studies, i.e. studies performed in Asian settings included higher proportion of patients with microalbuminuria while two studies only enrolled patients with macroalbuminuria. There was a significant difference in baseline SBP, DBP, and cholesterol levels among the studies. These risk factors were different among studies for diabetic complications however they did not differ within studies. The definition of microalbuminuria varied across studies. We were unable to perform the sensitivity analysis for diagnosis or severity of DKD due to the limited number of studies identified. Despite this limitation, results across the studies were consistent for any of the clinical or biochemical outcomes. We did not find any data on outcome measurements such as time to ESKD, and only limited data on all‐cause mortality. The reason may be such outcomes are difficult to implement on a practical basis. However, the considering slow disease progression of DKD, it would be difficult to extrapolate results of short duration changes on long‐term clinical outcomes. A systematic review found that increase in GFR and reduction in albuminuria were associated with lower mortality in advance kidney disease (Berhane 2011). We found that only one study with thiamine improved the albuminuria level compared to placebo. The remaining eight studies showed no improvement in GFR and albuminuria.

In the included studies, one of the major sources which would vary the actual amount of vitamin B intake is the dietary sources of vitamin B. Vitamin B can be obtained through various dietary sources, fortified foods etc. Majority of the studies did not ask the participants to change their diet habits in both of the group in individual studies. There is a high likelihood that the dietary source of vitamin B would be different among studies as dietary food habits across the countries vary widely. Asian, American, Canadian and European people have different food habits. In addition, food fortification programme has been implemented in the US and Canada. Hence, the participants for these countries may have higher level of vitamins.

Ethnicity/race is an important determinant of folate status under conditions of strictly controlled dietary folate intake (Perry 2004). Due to limited number of the studies, we were not able to perform subgroup analysis for a priori ethnicity subgroup. Other source of vitamin B and racial variation should be taken into consideration while designing future studies. One of the way to handle this confounding issue is to baseline monitoring of these vitamin B derivatives. In addition, urinary excretion of thiamine > 0.20 µmol/24 h indicates adequate dietary thiamine for adults (Finglas 1993). So, the level of such markers of adequate dietary thiamine sufficiency could serve as control parameter for dietary intake. The level of this vitamin at baseline would be an important criterion to consider for inclusion.

Quality of the evidence

Minimising the risk of bias is of major importance for a good quality systematic review. In this review, we therefore restricted the meta‐analysis to RCTs, ideally with proper randomisation, allocation concealment, blinding and freedom from selective reporting. However, not all the studies fulfilled this criteria. Three studies (Agha 2009; Alkhalaf 2010; Wotherspoon 2008) did not clearly report the methods used for sequence generation and allocation (selection bias) and were judge to have unclear risk of bias. The remaining six studies were at low risk of selection bias (DIVINe Study 2010; Lewis 2012; PYR‐205 Study 2007; PYR‐206 Study 2007; PYR‐207 Study 2007; Rabbani 2009). Two studies (DIVINe Study 2010; Rabbani 2009) reported blinding of patient, caregiver and observer and were at low risk of performance and detection bias. Two studies were at high risk of performance and detection bias (Agha 2009; Wotherspoon 2008) and the other five studies had unclear risk of performance bias and detection bias (Alkhalaf 2010; Lewis 2012; PYR‐205 Study 2007; PYR‐206 Study 2007; PYR‐207 Study 2007). Attrition bias was high in one study (DIVINe Study 2010), unclear in one study (Wotherspoon 2008) and low in seven studies (Agha 2009; Alkhalaf 2010; Lewis 2012; PYR‐205 Study 2007; PYR‐206 Study 2007; PYR‐207 Study 2007; Rabbani 2009). Reporting bias was high in one study (Wotherspoon 2008), unclear in one study (Agha 2009) and low in the remaining seven studies (Alkhalaf 2010; DIVINe Study 2010; Lewis 2012; PYR‐205 Study 2007; PYR‐206 Study 2007; PYR‐207 Study 2007; Rabbani 2009). Four studies funded by pharmaceutical companies were judged to be at high risk bias (Lewis 2012; PYR‐205 Study 2007; PYR‐206 Study 2007; PYR‐207 Study 2007), three were at low risk of bias (Agha 2009; Alkhalaf 2010; Rabbani 2009), and two were unclear (DIVINe Study 2010; Wotherspoon 2008).

Potential biases in the review process

We found many large scale studies performed in diabetic patients especially the HOPE‐2 Study 2006, and there may be a significant proportion of patients with DKD. However, we had to exclude those studies to remove misclassification bias in the review. It has been demonstrated from observational studies that blood pressure control or blood glucose control also prevents or reverses microalbuminuria (ADVANCE 2008). None of the clinical studies addressed the issues of these underlying confounders.

Agreements and disagreements with other studies or reviews

As far as we could ascertain, this is the first systematic review investigating vitamin B therapy for DKD.

Authors' conclusions

Implications for practice.

Currently, there is an absence of evidence to recommend the use of vitamin B therapy alone or combination for delaying the progression of DKD. Thiamine was found to be beneficial in reduction in albuminuria in a single study; there was however a lack of any improvement in kidney functions, and blood pressure following the use of vitamin B preparations alone or in combination. These findings require further confirmation given the limitations of small number and poor quality of the available studies.

Implications for research.

There is a lack of evidence of short‐term or long‐term benefits of vitamin B compared to placebo or losartan on clinical and biochemical outcomes. There were several limitations of available evidence: small number of studies with poor design; the duration of treatment and the period of observation were too short in some of the studies to detect therapeutic changes; and confounding bias with the use of dietary or fortified sources of vitamin B. In addition, the doses of vitamin B were higher than the recommended daily allowance in all included studies (recommended daily allowance: thiamine (1 mg/d), folate (400 μg/d), vitamin B₁₂ (2.4 μg/d)). It is not known whether the adequate dose for treatment approximates or is higher than the recommended daily allowance for specific types of vitamin B. Experimental studies showed that a high dose of vitamin B therapy may delay the progression of kidney impairment. Hence, there is a need for selection of optimum dosage regimens of different vitamin B preparation for delaying progression of kidney impairment in patients. In future, high quality RCTs are needed to establish efficacy and safety profile of vitamin B therapy especially treatment used in addition to the first line treatment. Studies should specify the rationale for selecting a particular vitamin B derivative and dose combinations for different stages of DKD.

What's new

Date	Event	Description
21 January 2015	Amended	Minor amendment to study references

Appendices

Appendix 1. Electronic search strategies

Database	Search terms
CENTRAL	MeSH descriptor Vitamin B Complex explode all trees (thiamin*):ti,ab,kw or (benfotiamin*):ti,ab,kw in Clinical Trials (niacin*):ti,ab,kw in Clinical Trials (riboflavin*):ti,ab,kw in Clinical Trials (folic acid):ti,ab,kw in Clinical Trials (folate*):ti,ab,kw in Clinical Trials (cobalamin*):ti,ab,kw in Clinical Trials (biotin*):ti,ab,kw in Clinical Trials (neurobion*):ti,ab,kw in Clinical Trials (pantothenic acid*):ti,ab,kw in Clinical Trials (pyridox*):ti,ab,kw in Clinical Trials (vitamin b*):ti,ab,kw in Clinical Trials (#1 OR #2 OR #3 OR #5 OR #6 OR #7 OR #8 OR #9 OR #10 OR #11 OR #12) MeSH descriptor Diabetic Nephropathies, this term only (diabetic or diabetes):ti,ab,kw in Clinical Trials (kidney or renal or nephropath* or proteinur* or microalbumin* or albuminur*):ti,ab,kw in Clinical Trials (#15 AND #16) (#14 OR #17) (#13 AND #18)
MEDLINE (OVID)	exp Vitamin B Complex/ thiamin$.tw. niacin$.tw. riboflavin$.tw. folic acid.tw. folate$.tw. cobalamin$.tw. biotin$.tw. neurobion$.tw. pantothenic acid.tw. pyridox$.tw. benfotiamine.tw. vitamin b.tw. (vitamin b1 or "vitamin b 1").tw. (vitamin b2 or "vitamin b 2").tw. (vitamin b3 or "vitamin b 3").tw. (vitamin b5 or "vitamin b 5").tw. (vitamin b6 or "vitamin b 6").tw. (vitamin b7 or "vitamin b 7").tw. (vitamin b9 or "vitamin b 9").tw. (vitamin b12 or "vitamin b 12").tw. or/1‐21 Diabetic Nephropathies/ ((diabetes or diabetic) and (kidney$ or renal or nephro$ or nephriti$ or glomerulo$ or albuminur$)).tw. or/23‐24 and/22,25
EMBASE (OVID)	exp vitamin b group/ thiamin$.tw. niacin$.tw. riboflavin$.tw. folic acid.tw. folate$.tw. cobalamin$.tw. biotin$.tw. neurobion$.tw. pantothenic acid.tw. pyridox$.tw. benfotiamine.tw. or/1‐12 diabetic nephropathy/ ((diabetes or diabetic) and (kidney$ or renal or nephro$ or nephriti$ or glomerulo$ or albuminur$)).tw. or/14‐15 and/13,16

Appendix 2. Risk of bias assessment tool

Potential source of bias	Assessment criteria
Random sequence generation Selection bias (biased allocation to interventions) due to inadequate generation of a randomised sequence	Low risk of bias: Random number table; computer random number generator; coin tossing; shuffling cards or envelopes; throwing dice; drawing of lots; minimization (minimization may be implemented without a random element, and this is considered to be equivalent to being random).
	High risk of bias: Sequence generated by odd or even date of birth; date (or day) of admission; sequence generated by hospital or clinic record number; allocation by judgement of the clinician; by preference of the participant; based on the results of a laboratory test or a series of tests; by availability of the intervention.
	Unclear: Insufficient information about the sequence generation process to permit judgement.
Allocation concealment Selection bias (biased allocation to interventions) due to inadequate concealment of allocations prior to assignment	Low risk of bias: Randomisation method described that would not allow investigator/participant to know or influence intervention group before eligible participant entered in the study (e.g. central allocation, including telephone, web‐based, and pharmacy‐controlled, randomisation; sequentially numbered drug containers of identical appearance; sequentially numbered, opaque, sealed envelopes).
	High risk of bias: Using an open random allocation schedule (e.g. a list of random numbers); assignment envelopes were used without appropriate safeguards (e.g. if envelopes were unsealed or non‐opaque or not sequentially numbered); alternation or rotation; date of birth; case record number; any other explicitly unconcealed procedure.
	Unclear: Randomisation stated but no information on method used is available.
Blinding of participants and personnel Performance bias due to knowledge of the allocated interventions by participants and personnel during the study	Low risk of bias: No blinding or incomplete blinding, but the review authors judge that the outcome is not likely to be influenced by lack of blinding; blinding of participants and key study personnel ensured, and unlikely that the blinding could have been broken.
	High risk of bias: No blinding or incomplete blinding, and the outcome is likely to be influenced by lack of blinding; blinding of key study participants and personnel attempted, but likely that the blinding could have been broken, and the outcome is likely to be influenced by lack of blinding.
	Unclear: Insufficient information to permit judgement
Blinding of outcome assessment Detection bias due to knowledge of the allocated interventions by outcome assessors.	Low risk of bias: No blinding of outcome assessment, but the review authors judge that the outcome measurement is not likely to be influenced by lack of blinding; blinding of outcome assessment ensured, and unlikely that the blinding could have been broken.
	High risk of bias: No blinding of outcome assessment, and the outcome measurement is likely to be influenced by lack of blinding; blinding of outcome assessment, but likely that the blinding could have been broken, and the outcome measurement is likely to be influenced by lack of blinding.
	Unclear: Insufficient information to permit judgement
Incomplete outcome data Attrition bias due to amount, nature or handling of incomplete outcome data.	Low risk of bias: No missing outcome data; reasons for missing outcome data unlikely to be related to true outcome (for survival data, censoring unlikely to be introducing bias); missing outcome data balanced in numbers across intervention groups, with similar reasons for missing data across groups; for dichotomous outcome data, the proportion of missing outcomes compared with observed event risk not enough to have a clinically relevant impact on the intervention effect estimate; for continuous outcome data, plausible effect size (difference in means or standardized difference in means) among missing outcomes not enough to have a clinically relevant impact on observed effect size; missing data have been imputed using appropriate methods.
	High risk of bias: Reason for missing outcome data likely to be related to true outcome, with either imbalance in numbers or reasons for missing data across intervention groups; for dichotomous outcome data, the proportion of missing outcomes compared with observed event risk enough to induce clinically relevant bias in intervention effect estimate; for continuous outcome data, plausible effect size (difference in means or standardized difference in means) among missing outcomes enough to induce clinically relevant bias in observed effect size; ‘as‐treated’ analysis done with substantial departure of the intervention received from that assigned at randomisation; potentially inappropriate application of simple imputation.
	Unclear: Insufficient information to permit judgement
Selective reporting Reporting bias due to selective outcome reporting	Low risk of bias: The study protocol is available and all of the study’s pre‐specified (primary and secondary) outcomes that are of interest in the review have been reported in the pre‐specified way; the study protocol is not available but it is clear that the published reports include all expected outcomes, including those that were pre‐specified (convincing text of this nature may be uncommon).
	High risk of bias: Not all of the study’s pre‐specified primary outcomes have been reported; one or more primary outcomes is reported using measurements, analysis methods or subsets of the data (e.g. subscales) that were not pre‐specified; one or more reported primary outcomes were not pre‐specified (unless clear justification for their reporting is provided, such as an unexpected adverse effect); one or more outcomes of interest in the review are reported incompletely so that they cannot be entered in a meta‐analysis; the study report fails to include results for a key outcome that would be expected to have been reported for such a study.
	Unclear: Insufficient information to permit judgement
Other bias Bias due to problems not covered elsewhere in the table	Low risk of bias: The study appears to be free of other sources of bias.
	High risk of bias: Had a potential source of bias related to the specific study design used; stopped early due to some data‐dependent process (including a formal‐stopping rule); had extreme baseline imbalance; has been claimed to have been fraudulent; had some other problem.
	Unclear: Insufficient information to assess whether an important risk of bias exists; insufficient rationale or evidence that an identified problem will introduce bias.

Data and analyses

Comparison 1. Vitamin B versus placebo.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 All‐cause mortality	4		Risk Ratio (M‐H, Random, 95% CI)	Totals not selected
1.1 PYR 100 mg/d (6 months)	1		Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
1.2 PYR 300 mg/d (12 months)	1		Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
1.3 PYR 500 mg/d (5 months)	1		Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
1.4 PYR 600 mg/d (12 months)	1		Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
1.5 Combined vitamin B therapy (36 months)	1		Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
2 Creatinine clearance	1		Mean Difference (IV, Random, 95% CI)	Totals not selected
2.1 Benfotiamine (12 weeks)	1		Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
3 Serum creatinine	3		Mean Difference (IV, Random, 95% CI)	Totals not selected
3.1 Benfotiamine (12 weeks)	1		Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
3.2 PYR 300 mg/d (12 months)	1		Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
3.3 PYR 600 mg/d (12 months)	1		Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
3.4 PYR 100/500 mg/d combined data (6 months)	1		Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
4 Proteinuria	2		Mean Difference (IV, Random, 95% CI)	Totals not selected
4.1 Combined vitamin B therapy (36 months)	1		Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
4.2 PYR 300 mg/d (12 months)	1		Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
4.3 PYR 600 mg/d (12 months)	1		Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
5 GFR	3		Mean Difference (Random, 95% CI)	Totals not selected
5.1 Combined vitamin B therapy (36 months)	1		Mean Difference (Random, 95% CI)	0.0 [0.0, 0.0]
5.2 PYR 300 mg/d (12 months)	1		Mean Difference (Random, 95% CI)	0.0 [0.0, 0.0]
5.3 PYR 600 mg/d (12 months)	1		Mean Difference (Random, 95% CI)	0.0 [0.0, 0.0]
5.4 Thiamine 300 mg/d (3 months)	1		Mean Difference (Random, 95% CI)	0.0 [0.0, 0.0]
6 Patients requiring dialysis	1		Risk Ratio (M‐H, Random, 95% CI)	Totals not selected
6.1 Combined vitamin B therapy (36 months)	1		Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
7 Systolic blood pressure	3		Mean Difference (IV, Random, 95% CI)	Totals not selected
7.1 Benfotiamine (12 weeks)	1		Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
7.2 Combined vitamin B therapy (36 months)	1		Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
7.3 Thiamine (12 weeks)	1		Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
8 Diastolic blood pressure	3		Mean Difference (IV, Random, 95% CI)	Totals not selected
8.1 Benfotiamine (12 weeks)	1		Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
8.2 Combined vitamin B therapy (36 months)	1		Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
8.3 Thiamine (12 weeks)	1		Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
9 One or more adverse events per patient	4		Risk Ratio (M‐H, Random, 95% CI)	Totals not selected
9.1 Adverse events	3		Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
9.2 Severe adverse events	2		Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
9.3 Serious adverse events	3		Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
10 Urinary albumin excretion [mg/24 h]			Other data	No numeric data
11 Serum creatinine [mg/dL]			Other data	No numeric data
12 Creatinine clearance [mL/min]			Other data	No numeric data

1.10. Analysis.

Comparison 1 Vitamin B versus placebo, Outcome 10 Urinary albumin excretion [mg/24 h].

Urinary albumin excretion [mg/24 h]
Study	Thiamine Baseline; median (minimum–maximum)	Placebo Baseline; median (minimum–maximum)	Thiamine End‐point; median (minimum‐maximum)	Placebo End‐point; median (minimum‐maximum)	p‐value; change from baseline
Rabbani 2009	43.7 (33.0–120.9)	43.7 (33.0–120.9)	30.1 (12.0–38.2)	35.5 (6.4–82.0)	p < 0.01

1.11. Analysis.

Comparison 1 Vitamin B versus placebo, Outcome 11 Serum creatinine [mg/dL].

Serum creatinine [mg/dL]
Study	Pyridoxamine 100 mg Baseline; mean (SD)	Placebo Baseline; mean (SD)	Pyridoxamine 100 mg End‐point; rate of rise/y	Placebo End‐point; rate of rise/y	p‐value
PYR‐206 Study 2007	1.27 (0.35)	1.33 (0.37)	0.178	0.223

1.12. Analysis.

Comparison 1 Vitamin B versus placebo, Outcome 12 Creatinine clearance [mL/min].

Creatinine clearance [mL/min]
Study	Pyridoxamine 100 mg Baseline; mean (SD)	Placebo Baseline; mean (SD)	Pyridoxamine 100 mg End‐point; rate of decrease/y	Placebo End‐point; rate of decrease/yr	p‐value
PYR‐206 Study 2007	99.9 (47)	104.2 (60)	17	31	p < 0.0001

Comparison 2. Vitamin B versus active control.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Serum creatinine	1		Mean Difference (IV, Random, 95% CI)	Totals not selected
1.1 Vitamin B12 versus ARB (6 months)	1		Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
2 UAE	1		Mean Difference (IV, Random, 95% CI)	Totals not selected
2.1 Vitamin B12 versus ARB (6 months)	1		Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
3 Systolic blood pressure	1		Mean Difference (IV, Random, 95% CI)	Totals not selected
3.1 Vitamin B12 versus ARB (months)	1		Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]
4 Diastolic blood pressure	1		Mean Difference (IV, Random, 95% CI)	Totals not selected
4.1 Vitamin B12 versus ARB (6 months)	1		Mean Difference (IV, Random, 95% CI)	0.0 [0.0, 0.0]

Characteristics of studies

Characteristics of included studies [ordered by study ID]

Agha 2009.

Methods	Study design: parallel RCT Study duration: 27 June 2006 to 2 April 2007 Duration of follow‐up: 8 months
Participants	Setting: diabetic outpatient clinic Country: Pakistan Type 2 DM for at least 2 years. DKD was defined as UAE 200 µg/min or 24 hr urinary albumin 30 to 300 mg/dL; normotensive patients (BP < 140/90 mm Hg, with BP lowering target of < 130/80 mm Hg in hypertensive adults with DM) Number: treatment group (171); control group (190) Mean age ± SD (years): treatment group (54.7 ± 10.9); control group (53.9 ± 11.1) Sex (M/F): treatment group (90/81); control group (NS) Co‐morbidities: NS  Exclusion criteria: proteinuria or non‐DKD; history of hypersensitivity reaction with losartan; postural hypotension with systolic postural BP drop > 20 mm Hg; pregnant women; poorly controlled diabetics (at least two episodes of symptomatic hypoglycaemia or blood glucose level > 400 mg/dL on follow‐up or baseline HbA1c > 8%); myocardial infraction or cerebrovascular events within past year, unstable angina pectoris, symptomatic heart failure, atrioventricular conduction disturbance, sick sinus syndrome, atrial fibrillation or other clinically significant rhythm disturbances; AKI; chronic glomerulonephritis; polycystic kidney disease; those with SCr > 1.5 mg/dL
Interventions	Treatment group Oral vitamin B12 mecobalamin: 500 µg/d for 6 months Control group Oral losartan: 50 mg/d for 6 months Co‐interventions NS
Outcomes	Change from the baseline in microalbuminuria
Notes	In‐house funding Language of publication: English Publication status (peer review journal): no Publication status (journal supplement): no Publication status (abstract): yes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Study did not mention in detail about random sequence generation rather mention only word "randomly"; however under the heading "Limitations" the authors state "Our study was a single centre, non‐randomized study..."
Allocation concealment (selection bias)	Unclear risk	Did not mention the method for allocation concealment
Blinding of participants and personnel (performance bias) All outcomes	High risk	Single blinding was used
Blinding of outcome assessment (detection bias) All outcomes	High risk	They did not mention details about the blinding of either patients or outcome assessor
Incomplete outcome data (attrition bias) All outcomes	Low risk	Yes, per protocol analysis was used
Selective reporting (reporting bias)	Unclear risk	Sufficient data was not available to assess the reporting bias from the publication. No prior protocol was available
Other bias	Low risk	Study was free from other sources of bias

Alkhalaf 2010.

Methods	Study design: parallel RCT Study duration: December 2007 to June 2009 Duration of follow‐up: 12 weeks
Participants	Country: The Netherlands Setting: multicentre Active DKD (defined as UAE 15 to 300 mg/24 h or equivalent ACR (males 1.2 to 25, females 1.75 to 35 mg/mmol) in 2 of 3 samples within 2 to 6 weeks despite ACEIs or ARBs, or both in unchanged dose for at least 3 months Number: treatment group (39); control group (43) Mean age ± SD (years): treatment group (65.3 ± 5.9); control group (64.6 ± 6.1) Sex (M/F): treatment group (30/9); control group (33/10) Other relevant information (e.g. co‐morbidities): NS Exclusion criteria: kidney impairment by other causes than diabetes; stage of the disease more severe than indicated in inclusion criteria (macroalbuminuria or kidney insufficiency); severe hypoglycaemia during the last 3 months, needing help from another person; severe hepatopathy (laboratory values about 3 times higher than normal); endocrine disorders (e.g. hyper/hypothyroidism); BP > 160/90 mm Hg; severe cardiac function disturbances and severe heart rhythm disturbances; neoplasm's (excluding history of treated skin cancer of the type BCC or SCC); severe general diseases or mental disorders making the participation in the study impossible; drug abuse; female patients during pregnancy and lactation period and female patients with active menses during the past year; hypersensitivity to benfotiamine; HbA1c > 9.5%; use of thiamine containing supplements during the last 3 months; participation in another study within one month before joining the benfotiamine study
Interventions	Treatment group Oral benfotiamine: 300 mg, 3 times/d for 12 weeks  Control group Oral placebo: once a day for 12 weeks Co‐interventions: NS
Outcomes	Primary outcome Change in urinary excretion of kidney injury molecule‐1 and albumin Secondary outcomes Change in urinary excretion of: B2 microglobulin, macrophage inhibiting factor, monocyte chemo‐attractant protein‐1 Other advanced glycation end products (AGEs)
Notes	Language of publication: English Commercial funding: no Non‐commercial funding: yes; Canadian Institutes of Health Research (CIHR) Study medications prepared by Worwag Pharma (Boblingen, Germany) Publication status (peer review journal): yes Publication status (journal supplement): no Publication status (abstract): yes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Not reported
Allocation concealment (selection bias)	Unclear risk	Not reported
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Investigator, subjects and caregiver were blinded (Protocol). Only title suggests the study was double blind, it was not mentioned in the methodology of the final publication
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Not reported
Incomplete outcome data (attrition bias) All outcomes	Low risk	The proportion of missing outcomes compared with observed event risk not enough to have a clinically relevant impact on the intervention effect estimate
Selective reporting (reporting bias)	Low risk	All the outcomes stated in the protocol were reported
Other bias	Low risk	It was free from other sources of bias

DIVINe Study 2010.

Methods	Study design: parallel RCT Study duration: May 2001 and July 2007 Duration of follow‐up: 36 months
Participants	Setting: national multicentre, national (Nephrology and diabetes clinics) Country: Canada Type 1 or type 2 DM; clinical or histological diagnosis of DKD; UAE level of at least 300 mg/d or urinary protein level of at least 500 mg/d (based upon a 24 hour urine collection) within the past 24 months Number: treatment group (128); control group (124) Mean age ± SD (years): treatment group (60.7 ± 11.6); control group (60.1 ± 10.8) Sex (M/F): treatment group (90/29); control group (88/31) Exclusion criteria: starting on ACEi or ARB who has been taking the drug for less than 3 months; not expected to survive 3 years because of intercurrent cancer or other severe illness; expected to be non‐compliant; who will not adhere to the study visit protocol, who will not take the study vitamins or who will not discontinue previous multivitamin or B‐complex vitamin use; on dialysis or imminently expected to require dialysis; other known kidney disease that may impact on progression rate (i.e. renal artery stenosis or glomerular kidney disease such as membranous nephropathy); women of childbearing potential who are unwilling to practice a form of birth control for the duration on the study deemed appropriate by the Investigator; CrCl < 30 mL/min based on the Cockcroft‐Gault method or < 25 mL/min if the patient is currently on an ACEi or ARB (within 30 days prior to randomisation if < 35 mL/min or within 6 months if ≥ 35 mL/min)
Interventions	Treatment group Vitamin B therapy for 36 months Oral folic acid: 2.5 mg/d Oral vitamin B6: 25 mg/d Oral vitamin B12: 1 mg/d Control group Placebo for 36 months
Outcomes	Change in GFR using ⁹⁹Technetium‐DTPA (⁹⁹Tc‐diethylene‐triamine‐pentaacetic acid) Kidney outcomes (change from baseline in urea, creatinine, urinary albumin excretion, CrCl, progression to dialysis or transplantation) Vascular events (stroke, death, myocardial infarction, revascularization) Cognitive decline measured by the Mini‐Mental State Examination score Progression of carotid intima‐media thickness and plaque volume (London study centre only)
Notes	Funding source: NS Language of publication: English Publication status (peer review journal): yes Publication status (journal supplement): yes Publication status (abstract): yes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	"A computer‐generated randomisation list was generated by the trial biostatistician (M.E.) using permuted block sizes of 2 and 4, and was stratified by centre, sex, and baseline Cockcroft‐Gault formula creatinine clearance (50 vs 50 mL/min/1.73 m²; to convert to mL/s/m², multiply by 0.0167)"
Allocation concealment (selection bias)	Low risk	"B vitamins and matching placebos were bottled with participant numbers by pharmacy staff. As trial participants were given the next appropriately labelled bottle, all participants, research coordinators, and treating physicians remained blinded to the treatment assignment throughout the trial."
Blinding of participants and personnel (performance bias) All outcomes	Low risk	"All participants, research coordinators, and treating physicians remained blinded to the treatment assignment throughout the trial."
Blinding of outcome assessment (detection bias) All outcomes	Low risk	"Central laboratory reports were made available to attending physicians, and blinding was maintained by deleting the values for plasma total homocysteine, serum folate, and serum B12."
Incomplete outcome data (attrition bias) All outcomes	High risk	Data were analysed using a modified intention‐to‐treat approach, defined as participants who met all the inclusion criteria and none of the exclusion criteria, ingested their first tablet of medication, and had 1 or more post‐randomisation GFR efficacy measures. Multiple imputation techniques were used. However, participants for the comparison at the end of 36 months were less for biochemical outcomes
Selective reporting (reporting bias)	Low risk	All the outcomes stated in the protocol were reported
Other bias	Unclear risk	Funding source not stated; free from other sources of bias

Lewis 2012.

Methods	Study design: parallel RCT Study duration: August 2008 to August 2010 Duration of follow‐up: 52 weeks
Participants	Countries: USA, Israel, Australia Setting: multicentre (14 diabetes clinics) Type 2 DM patients with confirmed diagnosis using ADA criteria; a SCr 1.3 to 3.3 mg/dL (women) or 1.5 to 3.5 mg/dL (men) 24 hour urine ACR ≥ 1200 mg/g while receiving an ACEi or ARB at the maximum Food and Drug Administration; recommended dosage for > 3 months before the qualifying visit; stable antihypertensive therapy was required for 2 months before the qualifying visit, with seated systolic BP < 160 mm Hg and diastolic BP 90 mm Hg and a goal of ≤ 130/80 mm Hg Number: treatment group 1 (99); treatment group (105); control group (103) Mean age ± SD (years): treatment group 1 (63.8 ± 9.1); treatment group 2 (63.6 ± 10.4); control group (64.4 ± 9.0) Sex (M/F): treatment group 1 (78/27); treatment group 2 (80/26); control group (78/28) Exclusion criteria: NS
Interventions	Treatment group 1 Pyridoxamine dihydrochloride: 150 mg twice/d for 52 weeks Treatment group 2 Pyridoxamine dihydrochloride: 300 mg twice/d for 52 weeks Control group Placebo for 52 weeks Co‐medications ACEi or ARB
Outcomes	Change in SCr Change from baseline in GFR and proteinuria
Notes	Funding source: Nephrogenex Inc. Language of publication: English Publication status (peer review journal): yes Publication status (journal supplement): yes Publication status (abstract): yes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	"Patients who met the serum creatinine and protein‐to‐creatinine ratio inclusion criteria initially or after the run‐in period were randomly assigned to Pyridorin, 150mg twice daily; Pyridorin, 300 mg twice daily; or placebo twice daily at a 1:1:1 ratio using an interactive voice response system"
Allocation concealment (selection bias)	Low risk	Interactive voice response system was used to allow the allocation concealment
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Only the abstract of the study states it was double blind
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	It was unclear from the method about blinding of investigators or participants
Incomplete outcome data (attrition bias) All outcomes	Low risk	"Our primary end point was the determination of the change in serum creatinine concentration in the intent‐to‐treat population studied"
Selective reporting (reporting bias)	Low risk	Selective reporting was not present as outcomes stated in the protocol were reported in the final manuscript
Other bias	High risk	This study was funded by Nephrogenex Inc. The authors of the study received salaries from research grants from NephroGenex

PYR‐205 Study 2007.

Methods	Study design: parallel RCT Study duration: NS Duration of follow‐up: 24 weeks
Participants	Countries: Canada, UK, Belgium, South Africa Setting: international, multicentre (diabetes clinics) Patients aged 18 to 70 years; type 1 or type 2 DM and DKD (defined by clinical assessment and medical history, and as assessed by UAE > 300 mg/24 h (from a 12 hour overnight urine collection multiplied by 2)); SCr ≤ 2.0 mg/dL; diabetic retinopathy, and no other known or suspected aetiology for nephropathy; non‐pregnant and non‐lactating females with use of appropriate birth control in those of childbearing potential Number: treatment group (57); control group (27) Mean age ± SD (years): treatment group (52.3 ± 11.4); control group (51.3 ± 10.2) Sex (M/F): treatment group (90/32); control group (67/23)
Interventions	Treatment group Pyridoxamine: 250 mg twice/d Control group Placebo: twice/d Co‐medications ACEi and ARB, and the other drugs patients normally receive
Outcomes	Efficacy outcomes SCr change from baseline (mg/dL) TGF 1 % change from baseline AGEs carboxymethyl lysine change from baseline (mmol/mol Lys) AGEs carboxyethyl lysine change from baseline (mmol/mol Lys) Safety outcomes Adverse events Treatment‐related adverse events Discontinued due to adverse events Serious adverse events Treatment‐related serious adverse events Death
Notes	Funding source: BioStratum Inc. Language of publication: English Publication status (peer review journal): yes Publication status (journal supplement): no Publication status (abstract): yes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	"Patients who met the entry criteria were randomised by a central randomizations schedule for each study."
Allocation concealment (selection bias)	Low risk	"PYR‐205/207, randomizations was 2:1 by a central randomizations schedule"
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Not stated who were blinded to the study drug
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Not reported
Incomplete outcome data (attrition bias) All outcomes	Low risk	"The prospectively defined intent‐to‐treat (ITT) population for final data analysis included all enrolled patients who received at least one dose of the double‐blinded study drug."
Selective reporting (reporting bias)	Low risk	All the outcome stated in protocol were reported
Other bias	High risk	Financial support for this study was provided by BioStratum Inc

PYR‐206 Study 2007.

Methods	Study design: parallel RCT Study duration: NS Duration of follow‐up: 24 weeks
Participants	Country: USA Setting: national, multicentre (32 diabetes clinics) Patients aged 18 to 70 years; type 1 or type 2 DM and DKD (defined by clinical assessment and medical history, and as assessed by UAE > 300 mg/24 h (from a 12 hour overnight urine collection multiplied by 2)); SCr ≤ 2.0 mg/dL; diabetic retinopathy, and no other known or suspected aetiology for nephropathy; nonpregnant and non‐lactating females with use of appropriate birth control in those of childbearing potential Number: treatment group (65); control group (63) Age (mean ± SD): treatment group (52.3 ± 11.4); control group (51.3 ± 10.2) Sex (M/F): treatment group (90/32); control group (67/23)
Interventions	Treatment group Oral pyridoxamine: 50 mg twice/d Control group Placebo: twice/d Co‐medications ACEi and ARB, and the other drugs patients normally receive
Outcomes	Efficacy outcomes SCr change from baseline (mg/dL) TGF 1 % change from baseline AGEs carboxymethyl lysine change from baseline (mmol/mol Lys) AGEs carboxyethyl lysine change from baseline (mmol/mol Lys) Safety outcomes Adverse events Treatment‐related adverse events Discontinued due to adverse events Serious adverse events Treatment‐related serious adverse events Death
Notes	Funding source: BioStratum Inc. Language of publication: English Publication status (peer review journal): yes Publication status (journal supplement): No Publication status (abstract): yes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	"Patients who met the entry criteria were randomised by a central randomizations schedule for each study."
Allocation concealment (selection bias)	Low risk	"In PYR‐206, patients were randomised 1:1 and in PYR‐205/207, randomizations was 2:1. and used computer generated randomisation"
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Not stated who were blinded to the study drug
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Not reported
Incomplete outcome data (attrition bias) All outcomes	Low risk	"The prospectively defined intent‐to‐treat (ITT) population for final data analysis included all enrolled patients who received at least one dose of the double‐blinded study drug."
Selective reporting (reporting bias)	Low risk	All the outcomes mentioned in the protocol were reported in the outcomes.
Other bias	High risk	Financial support for this study was provided by BioStratum Inc.

PYR‐207 Study 2007.

Methods	Study design: parallel RCT Study duration: NS Duration of follow‐up: 24 weeks
Participants	Country: Canada, UK, Belgium, South Africa, USA Setting: international, multicentre (Diabetes clinics) Patients aged 18 to 70 years; type 1 or type 2 DM and DKD (defined by clinical assessment and medical history, and as assessed by UAE > 300 mg/24 h (from a 12 hour overnight urine collection multiplied by 2)); SCr ≤ 2.0 mg/dL; diabetic retinopathy, and no other known or suspected aetiology for nephropathy; nonpregnant and non‐lactating females with use of appropriate birth control in those of childbearing potential Number: treatment group (57); control group (27) Mean age ± SD (year): treatment group (52.3 ± 11.4); control group (51.3 ± 10.2) Sex (M/F): treatment group (90/32); control group (67/23)
Interventions	Treatment group Oral pyridoxamine: 250 mg twice/d Control group Placebo: twice/d Co‐interventions ACEi and ARB, and the other drugs patients normally receive
Outcomes	Efficacy outcomes SCr change from baseline (mg/dL) TGF: 1 % change from baseline AGEs carboxymethyl lysine change from baseline (mmol/mol Lys) AGEs carboxyethyl lysine change from baseline (mmol/mol Lys) Safety outcomes Adverse events Treatment‐related adverse events Discontinued due to adverse events Serious adverse events Treatment‐related serious adverse events Death
Notes	Funding source: BioStratum Inc. Language of publication: English Publication status (peer review journal): yes Publication status (journal supplement): No Publication status (abstract): yes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	"Patients who met the entry criteria were randomised by a central randomizations schedule for each study."
Allocation concealment (selection bias)	Low risk	"In PYR‐206, patients were randomised 1:1 and in PYR‐205/207, randomizations was 2:1." PYR‐205 used central randomisation, which would be the case in PYR‐205/207.
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Not stated who were blinded to the study drug
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Not reported
Incomplete outcome data (attrition bias) All outcomes	Low risk	"The prospectively defined intent‐to‐treat (ITT) population for final data analysis included all enrolled patients who received at least one dose of the double‐blinded study drug."
Selective reporting (reporting bias)	Low risk	All the outcomes stated in protocol were reported
Other bias	High risk	Financial support for this study was provided by BioStratum Inc

Rabbani 2009.

Methods	Study design: parallel RCT Study duration: October 2006 and December 2006 Duration of follow‐up: 3 months
Participants	Country: Pakistan Setting: diabetes clinic Patients aged 35 to 65 years; type 1 DM; duration of type 2 DM > 5 years; BMI: 19 to 44 kg/m²; microalbuminuria (AER 30 to 299 mg/24 h) Number: treatment group (20); control group (20) Age (mean ± SD): treatment group (52.7 ± 8.4); control group (52.4 ± 8.7) Sex (M/F): treatment group (10/10); control group (11/09) Exclusion criteria: ESKD (creatinine > 2 mg/dL); severe hepatopathy (laboratory values about 3 times higher than normal); female patients during pregnancy and lactation period and female patients with active menses during the past year; women of childbearing potential who are unwilling to practice a form of birth control for the duration on the study; participation in another study within one month before joining the benfotiamine study; allergy or intolerance to thiamine; other significant morbidities
Interventions	Treatment group Thiamine: 3 x 100 mg/d for 3 months Control group Placebo: 3 tables/d for 3 months Co‐medications Insulin, hypoglycaemic agents (sulphonylureas, metformin, thiazolidinedione), antihypertensive drugs, cholesterol lowering drugs
Outcomes	Urinary excretion of albumin (24 h collection) (measured by immuno turbidimetry (Randox, Crumlin, UK)) Plasma cholesterol and triglycerides (determined by the Dimension Clinical Chemistry Analyzer method)
Notes	Funding source: Higher Education Commission, Pakistan & Warwick Medical School, University of Warwick Language of publication: English Publication status (peer review journal): yes Publication status (journal supplement): no Publication status (abstract): yes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Random number method was used to generate randomisation sequence
Allocation concealment (selection bias)	Low risk	"Randomisation was by central office in sequentially numbered opaque, sealed envelopes." Comment: Stated in the abstract of the publication but not in the main body of the text
Blinding of participants and personnel (performance bias) All outcomes	Low risk	"Participants, caregivers and those assessing the outcomes were blinded to group assignment" Comment: Stated in the abstract of the publication but not in the main body of the text
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Outcome assessor were blinded to assignment
Incomplete outcome data (attrition bias) All outcomes	Low risk	According to abstract of the publication, all the randomised patients were included in the analysis Numbers of patients in each group were included in the analysis not given in main body of the text.
Selective reporting (reporting bias)	Low risk	All the outcomes stated in the protocol were reported
Other bias	Low risk	Free from other sources of bias

Wotherspoon 2008.

Methods	Study design: parallel RCT Study duration: October 2006 and December 2006 Duration of follow‐up: 2 months
Participants	Country: UK Setting: single centre, national (diabetes clinic) Type 1 DM; DKD (defined by ACR > 2.5 mg/mmol in men and > 3.5 mg/mmol in women in a minimum of 2 of 3 early morning urine samples taken on separate days over a period of 3 months); presence of diabetic retinopathy; absence of cardiovascular disease Number: treatment group (9); control group (7) Mean age ± SD (years): treatment group (40.7 ± 9.4); control group (44.0 ± 12.8) Sex (M/F): treatment group (7/2); control group (4/3)
Interventions	Treatment group Folic acid: 5 mg once/d for 2 months Control group Placebo: once/d for 2 months
Outcomes	Plasma homocysteine Forearm blood flow Total antioxidant status Whole blood glutathione
Notes	Funding source: NS Language of publication: English Publication status (peer review journal): yes Publication status (journal supplement): no Publication status (abstract): yes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Insufficient information
Allocation concealment (selection bias)	Unclear risk	Insufficient information
Blinding of participants and personnel (performance bias) All outcomes	High risk	Insufficient information
Blinding of outcome assessment (detection bias) All outcomes	High risk	Insufficient information
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Insufficient information
Selective reporting (reporting bias)	High risk	Only reported biochemical outcomes not reported all of the outcomes measured.
Other bias	Unclear risk	Insufficient information

ACEi ‐ angiotensin‐converting enzyme inhibitors; ACR ‐ albumin:creatinine ratio; AKI ‐ acute kidney injury; ARB ‐ angiotensin receptor blockers; BCC ‐ basal cell carcinoma; BMI ‐ body mass index; BP ‐ blood pressure; DKD ‐ diabetic kidney disease; DM ‐ diabetic mellitus; ESKD ‐ end‐stage kidney disease; NS ‐ not stated; RCT ‐ randomised controlled trial; SCC ‐ squamous cell carcinoma; SCr ‐ serum creatinine; UAE ‐ urinary albumin excretion rate

Characteristics of excluded studies [ordered by study ID]

Study	Reason for exclusion
Ardalan 2003	RCT assessing the effects of vitamin B preparation in the patients with ESKD undergoing haemodialysis
Arnadottir 2003	RCT assessing the effects of vitamin B12 after each dialysis session in the folate‐replete haemodialysis patients with ESKD
Azadibakhsh 2009	RCT assessing efficacy of supplementation with high dose folic acid with and without vitamin B12 in lowering plasma total homocysteine concentrations in haemodialysis patients with ESKD
Biagini 2002	RCT assessing the effects of vitamin supplementation on the progression atherosclerosis in hyperhomocysteinaemia in kidney transplant recipients
Bostom 1996	RCT evaluating the effects on plasma homocysteine of adding supraphysiologic dose folic acid, vitamin B6, and vitamin B12 to the usual daily dosing of them in hyperhomocysteinaemia in dialysis patients with ESKD
Brensing 2003	RCT assessing the effects of vitamin B therapy hyperhomocysteinaemia in haemodialysis patients
Chang 2007	RCT assessing the effects of folic acid and vitamin B complex administration in patients on maintenance haemodialysis
Cheng 2008	RCT assessing the safety and efficacy of niacinamide in haemodialysis patients with high phosphorus levels
Chiu 2009	RCT assessing the effects of vitamin B preparations in patients on chronic haemodialysis therapy
De Angelis 2007	RCT assessing the effects of alternate vitamin supplementation with folic acid and vitamin B12 in haemodialysis patients
Dierkes 2001	RCT assessing the effects of various doses vitamins required for optimised treatment in ESKD patients treated with chronic intermittent maintenance haemodialysis
Dobronravov 2008	Clinical study assessing the effect of IV administration of sodium 2,3‐dimercaptopropane‐1‐sulfonate and 8‐week high‐dosed IV vitamin B therapy on total plasma homocysteine in patients undergoing chronic haemodialysis
Ducloux 2002	RCT evaluating the effects of IV or oral folinic acid and oral folic acid in haemodialysis patients
Farvid 2005	RCT assessing the effects of vitamins or mineral supplementation, or both other than vitamin B therapy on glomerular and tubular dysfunction in type 2 DM patients
Frank 1999	RCT assessing the pharmacokinetics profiles of two therapeutically used thiamine preparations in patients with ESKD
Frank 2000	RCT assessing the effects of benfotiamine in patients with ESKD
Gonin 2000	RCT comparing abnormally high doses of folic acid alone or with supplemental vitamin B6 and B12 compared with active folate alone or with serine in haemodialysis patients
Heinz 2009	Protocol including design and baseline data for RCT assessing effects of vitamins on cardiovascular morbidity and mortality in patients with ESKD
Henning 2001	RCT comparing the effects of a four‐week course of intravenous treatment with folate, cobalamin, and pyridoxal phosphate in haemodialysis patients
HOPE‐2 Study 2006	RCT assessing effects of vitamin B derivatives in all diabetic patients irrespective of their diabetic nephropathy status
Hyndman 2003	Study assessing the influence of genetic and nutritional status response to high‐dose vitamin B12 and folate treatment in ESKD patients with hyperhomocysteinaemia
Isbel 2003	RCT assessing the effects of vitamin B12 in the treatment of hyperhomocysteinaemia in patients with ESKD
Klemm 1994	Narrative review on the use of folate and vitamin B12 supplementation necessary in the chronic haemodialysis patients with erythropoietin treatment
Kuhlmann 2004	RCT assessing the effects of IV dose of vitamin therapy in hyperhomocysteinaemia in haemodialysis patients
Libetta 2004	RCT assessing the effects of vitamin therapy for hyperhomocysteinaemia in haemodialysis patients
Manns 2001	RCT assessing the effects of oral vitamin B12 for hyperhomocysteinaemia in haemodialysis patients
Manrique 2005	RCT assessing the effects of folic acid and Vitamin B for hyperhomocysteinaemia in kidney transplant patients
Marcucci 2002	RCT assessing the effects of vitamin supplements for hyperhomocysteinaemia in kidney transplant patients
Mazdeh 2005	RCT assessing the effects of folinic acid and folic acid with Vitamin B for hyperhomocysteinaemia in haemodialysis patients
Meng 2004	Clinical studies comparing dose of ginkgo leaf extract with vitamin B12 in patients with diabetic neuropathy. Studies did not assess the effects of Vitamin B12 alone or with placebo in the patients with diabetic neuropathy
Mydlik 1995	Study did not address treatment related to vitamin B in DKD
Nakamura 2003	RCT assessing the effects of folic acid and Vitamin B12 for hyperhomocysteinaemia in haemodialysis patients
Nakhoul 2004	RCT assessing the effects of folic acid and Vitamin B for hyperhomocysteinaemia in haemodialysis patients
Nascimento 2004	RCT assessing the efficacy of the thiamine in patients with haemodialysis
Okada 2000	RCT assessing the effects of vitamin B6 in the patients with haemodialysis
Pastore 2006	RCT assessing the effects of folic acid and Vitamin B12 in haemodialysis patients
Peng 2005	RCT assessing the effects of folic acid and IV vitamin B complex for hyperhomocysteinaemia in haemodialysis patients
Polkinghorne 2003	RCT assessing the effects of intramuscular vitamin B12 for hyperhomocysteinaemia in haemodialysis patients
Righetti 2006	Review on RCT assessing the effects of vitamin B treatment for hyperhomocysteinaemia in haemodialysis patients
Sanchez Alvarez 2005	RCT assessing the effects of vitamin B treatment for cardiovascular events in haemodialysis patients
Schupp 2008	Study assessing the effects of benfotiamine on genomic damage in peripheral lymphocytes in haemodialysis patients
Sjogren 1979	RCT assessing effect of high dose of thiamine on bone marrow morphology in patients on regular haemodialysis
Spoelstra 2004	RCT assessing the effects of vitamin B preparation among individuals with diabetes. None of the patients with diabetes had DKD at the baseline
Thambyrajah 2000	RCT assessing the effects of folic acid in patients with predialysis kidney failure
Tremblay 2000	RCT assessing the effects of folic acid in patients with ESKD
Tungkasereerak 2004	RCT assessing the effects of hydro soluble vitamins in patients with haemodialysis
Vrentzos 2001	RCT assessing the effects of vitamin B12 in patient with ESKD
Weissgarten 2001	RCT assessing the effects of vitamin B6 supplement in patient with haemodialysis
Xu 2005a	RCT assessing the effects of vitamin B supplement in kidney transplant recipient
Young 2009a	RCT assessing the effects of oral niacinamide in patient with peritoneal dialysis

DKD ‐ diabetic kidney disease; DM ‐ diabetes mellitus; ESKD ‐ end‐stage kidney disease; RCT ‐ randomised controlled trial

Characteristics of studies awaiting assessment [ordered by study ID]

NCT00737126.

Methods	The effect of folic acid administration in the progression of microalbuminuria
Participants	Country: Mexico Setting: single centre Inclusion criteria Type 2 DM patients with 5 to 15 years of diagnosis Microalbuminuria (defined as a urinary ACR between 30 and 300 mg/g) HbA1c ≤ 9% in the last year Exclusion criteria Acute diabetic complications HbA1c > 9% in the last year Acute infectious process Hepatic disease Thyroid disease
Interventions	Oral folic acid: 5 mg Placebo Titration period: NS
Outcomes	Primary outcomes Change in UAE from the baseline Secondary outcomes Change in serum homocysteine from the baseline Change in thrombomodulin from the baseline Change in von Willebrand factor from the baseline
Notes	Study Sponsor: Hospital Universitario Dr. Jose E. Gonzalez & Laboratorios Study has been completed, no results published

ACR ‐ albumin:creatinine ratio; DM ‐ diabetes mellitus; NS ‐ not stated; UAE ‐ urinary albumin excretion

Contributions of authors

1. Draft the protocol: ADR, DG, AR, DT

2. Study selection: DG, DT,

3. Extract data from studies: DG, DT

4. Enter data into RevMan: DG, DT

5. Carry out the analysis: DG, ADR, DT

6. Interpret the analysis: ADR, DG, DT, RW

7. Draft the final review: ADR, DG, AR, DT, RW

8. Disagreement resolution: ADR

9. Update the review: ADR, DG, AR, DT, RW

Sources of support

Internal sources

• Cochrane Renal Group, Australia.

External sources

• None, Other.

Declarations of interest

• Amit D Raval: none known

• Divyesh Thakker: none known

• Arohi N Rangoonwala: none known

• Deval Gor: none known

• Rama Walia: none known

Edited (no change to conclusions)