Abstract
Objective The main purpose of this article is to evaluate periodontal parameters of chronic periodontitis patients with uncontrolled type 2 diabetes mellitus after initial periodontal therapy plus vitamin C.
Materials and Methods A double-blind, placebo-controlled, clinical trial was conducted. Subjects received initial periodontal therapy plus 500 mg/day vitamin C for 2 months ( n = 15) or placebo ( n = 16). Fasting blood sugar (FBS), hemoglobin A1c (HbA1C), and plasma vitamin C level were assessed at baseline and 2 months post-treatment. Plaque Index, Sulcus Bleeding Index, Gingival Index, pocket depth, and clinical attachment level were measured at baseline, 1 month, and 2 months post-treatment.
Results Almost all subjects had low level of plasma vitamin C at baseline. In the test group, plasma vitamin C was significantly increased to an adequate level at the end of 2 months. After periodontal treatment, FBS and HbA1c were not significantly different compared with baseline in the test group. In the control group, FBS was significantly decreased from baseline. However, no significant difference between groups was found either in FBS or HbA1c. All periodontal parameters were significantly improved from baseline in both groups. However, no significant difference was found between groups.
Conclusion Supplementation of 500 mg/day vitamin C did not give an additional benefit in promoting periodontal status in periodontitis patients with uncontrolled type 2 diabetes mellitus.
Keywords: vitamin C, nonsurgical periodontal therapy, chronic periodontitis, uncontrolled type 2 DM
Introduction
The association between diabetes mellitus (DM) and periodontitis is generally accepted. 1 Several explanations underlying this association are proposed. These include an increased oxidative stress in diabetic patients, 2 an impaired neutrophil function, both the chemotaxis and phagocytosis 3 4 as well as the induction of proinflammatory cytokine and chemokine gene expression in monocytic cells. 5 Regarding the mucosal barrier function, thickening of gingival capillary basement membranes caused by microangiopathies impedes oxygen diffusion and metabolic waste elimination in the gingival tissues. 6 In addition, the cross-linking of collagen fibers is reduced, thereby reducing the flexibility and permeability of tissue. 7 On the other hand, the activity of collagenase is increased. 8 All of these are associated with more severe periodontal tissue destruction in diabetic subjects.
Vitamin C is one of the essential micronutrients for humans. It acts as an antioxidant and can promote wound healing. 9 In subjects with DM, plasma vitamin C was significantly lower compared with healthy individuals. 10 Low plasma vitamin C is due to an increase in clearance in patients with diabetic nephropathy. 11 The elevated plasma free radicals caused by hyperglycemia also reduce antioxidants including vitamin C. 12
Due to its antioxidation and wound healing promotion, the effect of vitamin C supplementation in DM patients with periodontitis should be of interest. However, few studies were found. 13 Gokhale et al 13 investigated the effect of vitamin C supplementation plus nonsurgical periodontal treatment on chronic periodontitis patients with freshly diagnosed type 2 DM. They reported a significant reduction in sulcus bleeding after dietary supplementation of 450 mg vitamin C. Although the beneficial effect of vitamin C was demonstrated, the follow-up period was only 2 weeks. 13 Thus, we aimed to evaluate, for 2 months, the effect of vitamin C as an adjunct in nonsurgical periodontal therapy in chronic periodontitis patients with uncontrolled type 2 DM.
Materials and Methods
This study was a double-blind, placebo-controlled clinical trial. Ethical approval was obtained from the Faculty of Dentistry/Faculty of Pharmacy, Mahidol University, Institutional Review Board (COA.No.MU-DT/PY-IRB 2016/061.0711) and Faculty of Medicine, Burapha University (No.001/2560). The study was registered in clinicaltrials.gov (NCT03269799).
Study Population
Type 2 DM subjects were recruited from Internal Medicine Clinic, Burapha University Hospital, Chonburi. Eligible subjects were informed and those who were willing to participate were referred to Dental Clinic, Burapha University Hospital for a comprehensive periodontal examination. Subjects who fulfilled the criteria were provided with a written informed consent. Before the experiment, oral hygiene instruction and motivation were given until Plaque Index 14 was ≤ 0.5.
Inclusion Criteria
Uncontrolled type 2 DM subjects were recruited (fasting blood sugar [FBS] of > 150 mg/dL and hemoglobin A1c [HbA1c] of > 7%). 15 Inclusion criteria for periodontitis were moderate chronic periodontitis (clinical attachment level (CAL) of ≥ 3 mm) according to the previous report 16 but slightly modified by selecting tooth with pocket depth (PD) of ≥ 5 mm in at least one tooth.
Exclusion Criteria
Subjects who affected with DM complications, receiving insulin injection 17 or medications that could interact with vitamin C 18 or suffered from any conditions that affected with vitamin C excretion, pregnancy, smoking, 19 receiving periodontal treatment or other vitamin supplementation in the previous 6 months.
Sample Size Calculation and Random Allocation
Sample size was calculated based on Sulcus Bleeding Index. 13 At a two-sided type I error of 0.05, 80% power of detection, a sample of 12 subjects was required. To compensate for 20% dropouts, at least 15 subjects were recruited for each group. Subjects were stratified by age and gender and randomly allocated by one researcher (SR) to the test (500 mg/day vitamin C) or control (placebo) group.
Baseline Examination
The study design was shown in ( Fig. 1 ). Blood samples were collected for the determination of plasma vitamin C, FBS, and HbA1c. Subjects saw medical doctors for DM follow-up. Periodontal parameters were recorded by a blinded and calibrated examiner (PK). Plaque Index, Gingival Index (GI), 20 Sulcus Bleeding Index, 21 PD, and CAL were recorded using a UNC-15 probe (Hu-Friedy, Illinois, United States) from one tooth with the deepest PD and without furcation involvement, periapical lesion, or endodontic involvement. Then, subjects received full mouth scaling and root planning and were prescribed 500 mg/day vitamin C (Government Pharmaceutical Organization, Thailand) or size- and color-identical placebo (Department of Pharmaceutical Industry, Faculty of Pharmacy, Mahidol University, Thailand). Vitamin C or placebo was kept in the concealed plastic bags and was prescribed for a duration of 30 days at a time.
Fig. 1.
Study design.
One-Month Evaluation
Periodontal parameters and any adverse effects were recorded. Residual vitamin C or placebo tablets were counted for an indirect evaluation of patients’ compliance. Vitamin C or placebo was prescribed for another 1 month.
Two-Month Evaluation
Blood sample was collected. Periodontal parameters were recorded. Residual vitamin C or placebo tablets were counted. Adverse effects, if any, were recorded.
Statistical Analysis
Data were analyzed using SPSS for Windows (version 23). Within and between group comparisons of plasma vitamin C, FBS and HbA1c were done using Wilcoxon signed rank test and Mann–Whitney U test, respectively. Within and between group, comparisons of periodontal parameters were done using Friedman test and Mann–Whitney U test, respectively. For multiple intragroup comparison, Bonferroni post-hoc test was performed. Significant level was set at p ≤ 0.05 for all tests.
Results
Thirty-one subjects were participated. None of them was withdrawn from the study. Subject characteristics at baseline were shown in ( Table 1 ). No statistical significance in subject characteristics was found between groups.
Table 1. Subject characteristics at baseline.
| Test ( n = 15) | Control ( n = 16) | |
|---|---|---|
| Age (years) | 59.87 ± 11.3 | 57.94 ± 14.0 |
| No. (%) of female | 11 (73.3) | 11 (68.8) |
| No. (%) of male | 4 (26.7) | 5 (31.3) |
| Duration of type 2 diabetes mellitus (year) | 7.86 ± 4.16 | 7.64 ± 4.42 |
Level of Plasma Vitamin C, Fasting Blood Sugar, and Hemoglobin A1c
At baseline, 73 and 68% of subjects in the test and control group, respectively, had deficient to low plasma vitamin C level (< 23 µmol/L according to Jacob and Sotoudeh 22 ). No significant difference in plasma vitamin C, FBS, and HbA1c was found between groups ( Table 2 ).
Table 2. Level of plasma vitamin C, fasting blood sugar, and hemoglobin A1c.
| Test | Control | p- Value | ||
|---|---|---|---|---|
| Abbreviations: FBS, fasting blood sugar; HbA1c, hemoglobin A1c. Statistical significance at p < 0.05. a Wilcoxon signed rank test. b Mann–Whitney U test. | ||||
| Plasma vitamin C (µmol/L) | Baseline | 18.54 ± 11.00 | 20.01 ± 18.84 | 0.599 |
| 2 months | 27.77 ± 15.55 | 17.40 ± 14.90 | 0.049 b | |
| Difference between baseline—2 months | 9.23 ± 14.57 | - 2.62 ± 9.31 | 0.017 b | |
| p- Value | 0.036 a | 0.179 | ||
| FBS (mg/dL) | Baseline | 168.53 ± 16.62 | 179 ± 49.04 | 0.654 |
| 2 months | 165.87 ± 51.76 | 170.13 ± 59.76 | 0.861 | |
| Difference between baseline—2 months | – 2.67 ± 52.81 | - 8.88 ± 36.08 | 0.953 | |
| p- Value | 0.280 | 0.046 a | ||
| HbA1c (%) | Baseline | 7.53 + 0.79 | 8.39 ± 1.50 | 0.202 |
| 2 months | 7.27 ± 0.88 | 7.98 ± 1.85 | 0.423 | |
| Difference between baseline—2 months | – 0.26 ± 0.80 | - 0.41 ± 0.89 | 0.599 | |
| p- Value | 0.279 | 0.059 | ||
At 2-month evaluation, plasma vitamin C in the test group was significantly elevated compared with baseline and the control group. In the test group, FBS and HbA1c were not significantly different compared with baseline. In the control group, FBS was significantly decreased from baseline. However, no significant difference between groups was found either in FBS or HbA1c.
Periodontal Parameters
At baseline, no any parameter was significantly different between groups ( Table 3 ). Throughout the study, subjects could control their oral hygiene status. Sulcus bleeding index, GI, PD, and CAL were significantly different compared with baseline, indicating periodontal improvement in both groups. However, no significant difference in all periodontal parameters was found between groups at any time interval.
Table 3. Periodontal parameters.
| Test | Control | p- Value | ||||||
|---|---|---|---|---|---|---|---|---|
|
Statistical significance at
p
< 0.05.
a Bonferroni post-hoc test. b Friedman test. | ||||||||
| Plaque Index | Baseline | 0.37 ± 0. 14 | } a | } a | 0.33 ± 0.11 | } a | } a | 0.358 |
| 1 month | 0.24 ± 0.11 | 0.26 ± 0.12 | 0.770 | |||||
| 2 months | 0.15 ± 0.07 | 0.16 ± 0.08 | 0.770 | |||||
| p- Value | <0.001 b | <0.001 b | ||||||
| Sulcus Bleeding Index | Baseline | 3.22 ± 0.46 | } a | } a | 3.00 ± 045 | } a | } a | 0.188 |
| 1 month | 1.9 ± 0.59 | 2.00 ± 0.57 | 0.861 | |||||
| 2 months | 0.57 ± 0.24 | 0.59 ± 0.24 | 0.830 | |||||
| p- Value | <0.001 b | <0.001 b | ||||||
| Gingival Index | Baseline | 1.04 ± 0.34 | } a | } a | 1.15 ± 0.32 | } a | } a | 0.401 |
| 1 month | 0.60 ± 0.16 | 0.66 ± 0.21 | 0.520 | |||||
| 2 months | 0.42 ± 0.09 | 0.45 ± 0.10 | 0.572 | |||||
| p -Value | <0.001 b | <0.001 b | ||||||
| Pocket depth (mm) | Baseline | 5.2 ± 0.41 | } a | } a | 5.63 ± 1.09 | } a | } a | 0.358 |
| 1 month | 3.25 ± 1.09 | 3.73 ± 1.09 | 0.151 | |||||
| 2 months | 3.25 ± 0.96 | 3.6 ± 0.90 | 0.232 | |||||
| p- Value | <0.001 b | <0.001 b | ||||||
| Clinical attachment level (mm) | Baseline | 5.31 ± 0.72 | } a | } a | 6.05 ± 1.73 | } a | } a | 0.247 |
| 1 month | 3.66 ± 1.51 | 4.13 ± 1.73 | 0.401 | |||||
| 2 months | 3.78 ± 1.17 | 3.93 ± 1.41 | 0.892 | |||||
| p- Value | 0.001 b | 0.001 b | ||||||
Adverse Effect and Compliance
No adverse effect was reported. Both groups complied to the course of vitamin C or placebo.
Discussion
Periodontitis is an inflammatory condition that enhances the generation of reactive oxygen species. 23 However, hyperglycemia increases free radical concentration, leading to the reduction in pancreatic β cell function and induction of insulin resistance and poor glycemic control. 12 Vitamin C, as an antioxidant, can decrease oxidative stress. 24 Along with its wound healing promotion effect, 24 25 we questioned that vitamin C supplementation plus nonsurgical periodontal therapy could improve periodontal parameters in subjects with uncontrolled type 2 DM.
In this study, vitamin C at a dose of 500 mg daily was chosen according to the previous studies. 13 26 Gokhale et al 13 reported that scaling and root planning plus 450 mg/day of vitamin C in chronic periodontitis subjects with freshly diagnosed type 2 DM resulted in a significant sulcus bleeding reduction. Levine et al 26 demonstrated that after single dose of 500 mg and higher, the bioavailability of vitamin C declined and excretion increased. At 1,000 mg of vitamin C, oxalate and urate excretion were elevated. 26
After initial periodontal treatment, periodontal health was improved without significant difference between groups. Our result was inconsistent to the previous study 13 and probably due to the difference in subject characteristics. Subjects in the study of Gokhale et al 13 were freshly diagnosed type 2 DM, while those in our study were uncontrolled type 2 DM. It is known that severity and progression of periodontal disease are increased in uncontrolled DM patients. 27 Moreover, some subjects in our study had an adequate plasma vitamin C level at baseline (data not shown). Thus, vitamin C supplementation to adequately nourished people might not affect with periodontal integrity. 22 28 These two factors might mask the beneficial effect of vitamin C.
Periodontitis and DM have a bidirectional relationship. 29 30 However, the effect of periodontal therapy on glycemic control was still in doubt 29 31 and was not the objective of the present study. It was shown that nonsurgical periodontal therapy in diabetic patients could reduce HbA1c by ~0.4%. 29 In this study, HbA1c was reduced after initial periodontal treatment, but the reduction was not significant in both groups. Our result was supported by Mizuno et al 31 that nonsurgical periodontal treatment improved systemic oxidative stress balance and quality of life, but did not significantly decrease HbA1c levels at 3 months follow-up in type 2 DM patients. 31 Indeed, level of glycemic control depends on factors other than periodontal treatment, for example, behavior, sugar and food intake, exercise, stress, use of hypoglycemic medication, duration of treatment, and level of education. 32 33 Another explanation is the study period of 2 months was inadequate to observe the change in glycemic control. Although the reduction in HbA1c was not statistically significant (0.26% in the test group and 0.41% in the control group), it could have a clinical impact since it could reduce the risk of microvascular complication and mortality rate by more than 10% at the population level. 34 Thus, we agreed with Casanova et al 29 that periodontal treatment should be a part of the overall management of DM. 29
Supplementation of 500 mg/day vitamin C for 2 months did not affect FBS and HbA1c in this study. This finding might be explained by the study of Yue et al 35 that both plasma ascorbic acid and its urinary excretion correlated inversely with glycosylated hemoglobin level. In addition, abnormalities of vitamin C metabolism and its higher turnover were found in diabetics patients over the normal volunteers. 36
In conclusion, supplementation of 500 mg/day vitamin C plus initial periodontal therapy in periodontitis subjects with uncontrolled type 2 DM did not give an additional benefit in promoting periodontal status.
Acknowledgments
The authors would like to thank the Faculty of Dentistry, Mahidol University for a grant of this study.
Footnotes
Conflict of Interest None declared.
References
- 1.Emrich L J, Shlossman M, Genco R J. Periodontal disease in non-insulin-dependent diabetes mellitus. J Periodontol. 1991;62(02):123–131. doi: 10.1902/jop.1991.62.2.123. [DOI] [PubMed] [Google Scholar]
- 2.Patil V S, Patil V P, Gokhale N, Acharya A, Kangokar P. Chronic periodontitis in type 2 diabetes mellitus: oxidative stress as a common factor in periodontal tissue injury. J Clin Diagn Res. 2016;10(04):BC12–BC16. doi: 10.7860/JCDR/2016/17350.7542. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 3.Golub L M, Nicoll G A, Iacono V J, Ramamurthy N S. In vivo crevicular leukocyte response to a chemotactic challenge: inhibition by experimental diabetes. Infect Immun. 1982;37(03):1013–1020. doi: 10.1128/iai.37.3.1013-1020.1982. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 4.Alba-Loureiro T C, Munhoz C D, Martins J O et al. Neutrophil function and metabolism in individuals with diabetes mellitus. Braz J Med Biol Res. 2007;40(08):1037–1044. doi: 10.1590/s0100-879x2006005000143. [DOI] [PubMed] [Google Scholar]
- 5.Shanmugam N, Reddy M A, Guha M, Natarajan R. High glucose-induced expression of proinflammatory cytokine and chemokine genes in monocytic cells. Diabetes. 2003;52(05):1256–1264. doi: 10.2337/diabetes.52.5.1256. [DOI] [PubMed] [Google Scholar]
- 6.Frantzis T G, Reeve C M, Brown A L.JrThe ultrastructure of capillary basement membranes in the attached gingiva of diabetic and nondiabetic patients with periodontal disease J Periodontol 19714207406–411. [DOI] [PubMed] [Google Scholar]
- 7.Paul R G, Bailey A J. Glycation of collagen: the basis of its central role in the late complications of ageing and diabetes. Int J Biochem Cell Biol. 1996;28(12):1297–1310. doi: 10.1016/s1357-2725(96)00079-9. [DOI] [PubMed] [Google Scholar]
- 8.Ramamurthy N S, Golub L M. Diabetes increases collagenase activity in extracts of rat gingiva and skin. J Periodontal Res. 1983;18(01):23–30. doi: 10.1111/j.1600-0765.1983.tb00331.x. [DOI] [PubMed] [Google Scholar]
- 9.Packer L, Fuchs J.Vitamin C in Health and Disease. New York: Marcel Dekker1997 [Google Scholar]
- 10.Will J C, Ford E S, Bowman B A. Serum vitamin C concentrations and diabetes: findings from the Third National Health and Nutrition Examination Survey, 1988-1994. Am J Clin Nutr. 1999;70(01):49–52. doi: 10.1093/ajcn/70.1.49. [DOI] [PubMed] [Google Scholar]
- 11.Hirsch I B, Atchley D H, Tsai E, Labbé R F, Chait A. Ascorbic acid clearance in diabetic nephropathy. J Diabetes Complications. 1998;12(05):259–263. doi: 10.1016/s1056-8727(97)00125-6. [DOI] [PubMed] [Google Scholar]
- 12.Ceriello A.Oxidative stress and glycemic regulation Metabolism 20004902Suppl 127–29. [DOI] [PubMed] [Google Scholar]
- 13.Gokhale N H, Acharya A B, Patil V S, Trivedi D J, Thakur S L. A short-term evaluation of the relationship between plasma ascorbic acid levels and periodontal disease in systemically healthy and type 2 diabetes mellitus subjects. J Diet Suppl. 2013;10(02):93–104. doi: 10.3109/19390211.2013.790332. [DOI] [PubMed] [Google Scholar]
- 14.Greene J C, Vermillion J R. The simplified oral hygiene index. J Am Dent Assoc. 1964;68:7–13. doi: 10.14219/jada.archive.1964.0034. [DOI] [PubMed] [Google Scholar]
- 15.American Diabetes Association . Standards of medical care in diabetes 2018. Diabetes Care. 2018;2018:41. [Google Scholar]
- 16.Wiebe C B, Putnins E E. The periodontal disease classification system of the American Academy of Periodontology–an update. J Can Dent Assoc. 2000;66(11):594–597. [PubMed] [Google Scholar]
- 17.Paolisso G, D’Amore A, Balbi Vet al. Plasma vitamin C affects glucose homeostasis in healthy subjects and in non-insulin-dependent diabetics Am J Physiol 1994266 (2 Pt 1E261–E268. [DOI] [PubMed] [Google Scholar]
- 18.Alagl A S, Bhat S G. Ascorbic acid: new role of an age-old micronutrient in the management of periodontal disease in older adults. Geriatr Gerontol Int. 2015;15(03):241–254. doi: 10.1111/ggi.12408. [DOI] [PubMed] [Google Scholar]
- 19.Schectman G, Byrd J C, Gruchow H W. The influence of smoking on vitamin C status in adults. Am J Public Health. 1989;79(02):158–162. doi: 10.2105/ajph.79.2.158. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 20.Loe H, Silness J. Periodontal disease in pregnancy. I. Prevalence and severity. Acta Odontol Scand. 1963;21:533–551. doi: 10.3109/00016356309011240. [DOI] [PubMed] [Google Scholar]
- 21.Mühlemann H R, Son S. Gingival sulcus bleeding—a leading symptom in initial gingivitis. Helv Odontol Acta. 1971;15(02):107–113. [PubMed] [Google Scholar]
- 22.Jacob R A, Sotoudeh G. Vitamin C function and status in chronic disease. Nutr Clin Care. 2002;5(02):66–74. doi: 10.1046/j.1523-5408.2002.00005.x. [DOI] [PubMed] [Google Scholar]
- 23.Wang Y, Andrukhov O, Rausch-Fan X. Oxidative stress and antioxidant system in periodontitis. Front Physiol. 2017;8:910. doi: 10.3389/fphys.2017.00910. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 24.Chapple I L. Potential mechanisms underpinning the nutritional modulation of periodontal inflammation. J Am Dent Assoc. 2009;140(02):178–184. doi: 10.14219/jada.archive.2009.0131. [DOI] [PubMed] [Google Scholar]
- 25.Mohammed B M, Fisher B J, Kraskauskas D et al. Vitamin C promotes wound healing through novel pleiotropic mechanisms. Int Wound J. 2016;13(04):572–584. doi: 10.1111/iwj.12484. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 26.Levine M, Conry-Cantilena C, Wang Y et al. Vitamin C pharmacokinetics in healthy volunteers: evidence for a recommended dietary allowance. Proc Natl Acad Sci USA. 1996;93(08):3704–3709. doi: 10.1073/pnas.93.8.3704. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 27.Ryan M E, Carnu O, Kamer A.The influence of diabetes on the periodontal tissues J Am Dent Assoc 2003134(Spec No)34S–40S. [DOI] [PubMed] [Google Scholar]
- 28.Vogel R I, Lamster I B, Wechsler S A, Macedo B, Hartley L J, Macedo J A. The effects of megadoses of ascorbic acid on PMN chemotaxis and experimental gingivitis. J Periodontol. 1986;57(08):472–479. doi: 10.1902/jop.1986.57.8.472. [DOI] [PubMed] [Google Scholar]
- 29.Casanova L, Hughes F J, Preshaw P M. Diabetes and periodontal disease: a two-way relationship. Br Dent J. 2014;217(08):433–437. doi: 10.1038/sj.bdj.2014.907. [DOI] [PubMed] [Google Scholar]
- 30.Preshaw P M, Alba A L, Herrera D et al. Periodontitis and diabetes: a two-way relationship. Diabetologia. 2012;55(01):21–31. doi: 10.1007/s00125-011-2342-y. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 31.Mizuno H, Ekuni D, Maruyama T et al. The effects of non-surgical periodontal treatment on glycemic control, oxidative stress balance and quality of life in patients with type 2 diabetes: a randomized clinical trial. PLoS One. 2017;12(11):e0188171. doi: 10.1371/journal.pone.0188171. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 32.Ahmad N S, Islahudin F, Paraidathathu T. Factors associated with good glycemic control among patients with type 2 diabetes mellitus. J Diabetes Investig. 2014;5(05):563–569. doi: 10.1111/jdi.12175. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 33.Yigazu D M, Desse T A. Glycemic control and associated factors among type 2 diabetic patients at Shanan Gibe Hospital, Southwest Ethiopia. BMC Res Notes. 2017;10(01):597. doi: 10.1186/s13104-017-2924-y. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 34.Simpson T C, Weldon J C, Worthington H V et al. Treatment of periodontal disease for glycaemic control in people with diabetes mellitus. Cochrane Database Syst Rev. 2015;(11):CD004714. doi: 10.1002/14651858.CD004714.pub3. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 35.Yue D K, McLennan S, McGill M et al. Abnormalities of ascorbic acid metabolism and diabetic control: differences between diabetic patients and diabetic rats. Diabetes Res Clin Pract. 1990;9(03):239–244. doi: 10.1016/0168-8227(90)90051-t. [DOI] [PubMed] [Google Scholar]
- 36.Som S, Basu S, Mukherjee D et al. Ascorbic acid metabolism in diabetes mellitus. Metabolism. 1981;30(06):572–577. doi: 10.1016/0026-0495(81)90133-5. [DOI] [PubMed] [Google Scholar]