The effect of cinnamon supplementation on cardiovascular risk factors in adults: a GRADE assessed systematic review, dose–response and meta-analysis of randomized controlled trials

Abstract

Background

Numerous clinical studies have suggested that cinnamon supplementation may be effective for cardiovascular disease risk factors, but the findings are controversial. This comprehensive systematic review and meta-analysis aimed to assess the impact of cinnamon supplementation on cardiovascular disease risk factors.

Methods

Relevant studies were identified through electronic searches of databases, including Web of Science, PubMed, Central, Scopus, and Embase, up to July 2024.

Results

Forty-nine studies were included. Cinnamon supplementation significantly reduced WC (SMD = − 0.40; 95% (CI): − 0.73, − 0.06), DBP (SMD = − 1.04; 95% CI: − 1.54, − 0.55), SBP (SMD = − 0.85; 95% CI: − 1.54, − 0.16), fasting glucose (SMD = − 1.28; 95% CI: − 1.65, − 0.90), fasting insulin (SMD = − 0.26; 95% CI: − 0.50, − 0.02), HbA1c (SMD = − 0.71; 95% CI: − 1.02, − 0.40), HOMA-IR (SMD = − 0.54; 95% CI: − 0.82, − 0.26), postprandial blood glucose (SMD = − 2.28; 95% CI: − 3.48, − 1.08), CRP (SMD = − 0.78; 95% CI: − 1.28, − 0.27), LDL-C (SMD = − 0.71; 95% CI: − 1.02, − 0.40), total cholesterol (TC) (SMD = − 1.15; 95% CI: − 1.55, − 0.75), triglycerides (TG) (SMD = − 0.91; 95% CI: − 1.25, − 0.56), and MDA (SMD = − 0.76; 95% CI: − 1.07, − 0.45). Additionally, cinnamon supplementation significantly elevated HDL-C levels (SMD = 0.56; 95% CI: 0.23, 0.89).

Conclusion

Cinnamon supplementation demonstrated significant benefits in improving cardiovascular risk factors. These findings suggest its potential as an adjunct therapy for improving cardiovascular disease risk factors.

Supplementary Information

The online version contains supplementary material available at 10.1186/s41043-025-00967-3.

Introduction

Cardiovascular diseases (CVDs) remain a leading cause of global mortality, with risk factors such as obesity, dyslipidemia, diabetes, and hypertension contributing significantly to their burden [1]. In 2023, the World Heart Federation reported that CVDs accounted for approximately 20.5 million deaths annually, underscoring the need for effective preventive strategies [2]. Lifestyle interventions, including dietary modifications, have gained attention for their potential to mitigate these risk factors [3, 4]. Among dietary components, spices like cinnamon (Cinnamomum verum and related species) have been investigated for their therapeutic effects on cardiovascular health due to their bioactive compounds [5–7].

Cinnamon, derived from the bark of trees in the Cinnamomum genus of the Lauraceae family, is widely used in culinary and medicinal applications across Asia, Australia, and South America [8]. Its key bioactive constituents, including cinnamaldehyde, cinnamic acid, and cinnamate, exhibit antioxidant, anti-inflammatory, and antidiabetic properties that may benefit cardiovascular health [9, 10]. Recent meta-analyses on cinnamon supplementation have shown mixed results. Fateh et al. (2024) found that while cinnamon had no significant effect on low-density lipoprotein cholesterol (LDL-C) levels and total cholesterol (TC), it significantly reduced triglycerides (TG) at doses below 500 mg/day [11]. Another review, covering 28 studies on patients with type 2 diabetes mellitus (T2DM), reported significant improvements in fasting blood glucose (FBG), hemoglobin A1c (HbA1c), and homeostatic model assessment for insulin resistance (HOMA-IR) with doses of 2 g/day or more, alongside benefits for lipid profiles and body mass index (BMI) [12]. However, a review of 23 studies found no significant changes in LDL-C or high-density lipoprotein cholesterol (HDL-C), suggesting limited impact on these specific cardiovascular markers [13]. Additionally, an umbrella review of seven meta-analyses highlighted substantial reductions in body weight and BMI at doses of 3 g/day or higher, although effects on waist circumference (WC) were less notable [14]. A more recent analysis confirmed that cinnamon supplementation could lower TG and LDL-C and increase HDL-C, but had no effect on FBG [15]. These inconsistencies highlight the need for a comprehensive, high-quality GRADE-assessed meta-analysis that integrates both subgroup and dose–response analyses to clarify cinnamon's true impact on cardiovascular risk factors.

Despite growing interest in cinnamon as a complementary therapy, consensus is lacking regarding its optimal dosing, long-term safety, and mechanisms of action across diverse populations. Moreover, most previous reviews have focused on single outcomes (e.g., glycemic control or lipid profile) rather than evaluating a broad spectrum of cardiovascular risk markers collectively. To address this literature gap, we conducted a systematic review and meta-analysis assessing the effects of cinnamon supplementation on multiple cardiovascular risk factors—including lipid profile, glycemic indices, blood pressure, and anthropometric measures—with an emphasis on dose–response relationships. By analyzing diverse subgroups and integrating dose–response data, we aim to clarify optimal dosages and therapeutic contexts for cinnamon use in CVD prevention. Our rigorous application of the GRADE framework ensures high-quality evidence, offering valuable guidance for healthcare professionals and policymakers in developing evidence-based strategies for cardiovascular health management.

Methods

Protocol and registration

This systematic review and meta-analysis was conducted according to a pre-specified protocol and adhered to the 2015 Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines [16]. The study is registered with the International Prospective Register of Systematic Reviews (PROSPERO), ensuring transparency and rigorous research standards. The registration number is CRD42024607218, available for public verification.

Literature search and study selection

A comprehensive literature search was conducted through July 2024 across several databases: Cochrane Central Register of Controlled Trials (Central), Web of Science, Medline, Scopus, and Embase. The search strategy targeted studies investigating cinnamon’s effects on health markers and used relevant MeSH and EMTREE terms such as “cinnamon” and “clinical trial” (Supplementary Table 1). We also examined references in key articles, systematic reviews, and meta-analyses for additional studies.

The primary outcomes assessed were body fat percentage (BF), BMI, WC, body weight, waist-to-hip ratio (WHR), diastolic (DBP) and systolic blood pressure (SBP), fasting glucose, fasting insulin, postprandial glucose, HbA1c, HOMA-IR, quantitative insulin sensitivity check index (QUICKI), C-reactive protein (CRP), interleukin-6 (IL-6), HDL-C, TC, TG, alanine transaminase (ALT), aspartate transaminase (AST), alkaline phosphatase (ALP), blood urea nitrogen (BUN), malondialdehyde (MDA), and total antioxidant capacity (TAC).

Inclusion/exclusion criteria and data extraction

Randomized controlled trials (RCTs) involving human participants were included if they used a placebo-controlled, parallel, or crossover design and were published in English with at least one week of intervention. Exclusion criteria included non-RCTs, animal and in vitro studies, observational studies (e.g., cohort, case–control, cross-sectional), reviews, case reports, conference abstracts, and editorials. Studies combining cinnamon with other interventions were excluded unless the effects of cinnamon could be independently analyzed. EndNote X7 software was used to consolidate search results and manage duplicates.

Two reviewers (H.M. and A.A.) independently screened titles and abstracts, followed by full-text reviews to assess eligibility according to inclusion criteria. Discrepancies were resolved with input from a third reviewer (A.J.). Data extraction was performed independently by two authors (A.J. and V.M.) using a standardized form to capture study characteristics, population demographics, intervention specifics, and outcome measures.

Quality assessment and evidence grading

The methodological quality of included studies was assessed using the Cochrane Risk of Bias tool, covering sequence generation, allocation concealment, blinding, incomplete outcome data, selective reporting, and other biases [17]. Two reviewers (H.M. and M.A.) conducted this assessment, with disagreements resolved through discussion or third-party consultation (A.J.).

The certainty of the evidence was evaluated using the GRADE approach, taking into account risk of bias, consistency, precision, directness, and additional factors (e.g., dose–response relationship, effect size) [18]. Evidence quality was rated as high, moderate, low, or very low for each outcome, with two reviewers (A.J. and H.M.) conducting assessments and a third reviewer (V.M.) consulted for unresolved discrepancies.

Statistical analysis

All statistical analyses were conducted using Stata version 17.0 (Stata Corp, College Station, Texas). Pre- and post-intervention means, standard deviations (SDs), and sample sizes from both intervention and control groups were used to estimate the effects of cinnamon supplementation. Standardized mean differences (SMDs) were calculated using a random-effects model to account for heterogeneity across studies, with the DerSimonian-Laird method applied for weighting [19].

When only baseline and endpoint values were reported without change SDs, the Follmann method was used to estimate SDs, assuming a correlation coefficient (R) of 0.5 [20]. For studies reporting standard errors, SDs were calculated as SD = SE × sqrt(n). Heterogeneity was assessed using the I² statistic, and prediction intervals were calculated to evaluate clinical relevance [21].

Subgroup analyses were conducted based on population characteristics, intervention duration, and cinnamon dosage to identify sources of heterogeneity. Meta-regression was used to examine the relationship between cinnamon dosage (g/day), duration, and cardiovascular outcomes [22]. A nonlinear model was applied to evaluate the dose–response association between cinnamon supplementation and health outcomes [23], offering insights into the effects of varying dosages and intervention durations on outcomes and helping to determine the dosage that yields the greatest benefit.

Leave-one-out sensitivity analysis was performed to test the robustness of findings by sequentially omitting each study and recalculating the pooled estimate. Egger's test was employed to evaluate publication bias.

Results

Study selection

The study selection process is illustrated in Fig. 1. Initially, 7,930 studies were identified through database searches. After removing 1,912 duplicates, 233 irrelevant studies, and 368 animal studies, 5,417 studies remained for title and abstract screening. Of these, 5,305 studies were excluded as irrelevant, resulting in 112 full-text articles for further assessment. After evaluating these, 64 studies were excluded due to non-relevant outcomes (Supplementary Table 2 shows detailed exclusion reasons). Ultimately, 49 studies with a total of 3,038 participants were included in the systematic review and meta-analysis [24–72].

Fig. 1.

Flowchart of study selection for inclusion trials in the systematic review

Study characteristics

The characteristics of the included studies are summarized in Table 1. Supplementary Figs. 1, 2, 3, 4,5,6 and 7 present the SMDs and 95% CIs for outcomes including BF, BMI, WC, weight, WHR, DBP, SBP, fasting glucose, fasting insulin, glucose, HbA1c, HOMA-IR, postprandial blood glucose, QUICKI, CRP, IL-6, HDL-C, LDL-C, TC, TG, ALP, ALT, AST, BUN, MDA, and TAC, along with their changes.

Table 1.

Characteristic of included studies in the meta-analysis

Studies. Year (Ref.)	Country	Study Design	Health Condition	Sample Size (Sex)	Sample Size (INT/CON)	Trial Duration (Week)	Means Age & BMI (INT/CON)	Dose of Supplement (mg/d)	Type of Supplement (INT/CON)	Outcomes
Khan et al. 2003[24]	Pakistan	R, PC	T2DM	60 (B)	10/10	6	Age 52.0 ± 5.85/ 52.0 ± 6.87 BMI: NR	1000	Capsule: (Cinnamomum cassia)/ Placebo (Wheat flour)	Fasting serum glucose, Fasting serum TG, Fasting serum cholesterol & Fasting serum LDL
					10/10		Age 52.0 ± 5.85/ 52.0 ± 6.87 BMI: NR	3000
					10/10		Age 52.0 ± 5.85/ 52.0 ± 6.87 BMI: NR	6000
Mang et al. 2006[25]	Germany	R, PC, DB	T2DM	65 (B)	33/32	16	Age: 62.8 ± 8.37/ 63.7 ± 7.17 BMI: 29.6 ± 4.64/30.1 ± 5.22	3000	Capsule: Aqueous cinnamon extract (Cinnamomum cassia)/ Placebo (Microcrystalline cellulose)	FPG, HbA1c, TC, LDL, HDL & TG
Vanschoonbeek et al. 2006[26]	Netherlands	R, PC, DB	T2DM	25 (F)	12/13	6	Age: 62 ± 6.92/ 64 ± 7.21 BMI: 30.7 ± 3.81/ 30.1 ± 5.04	1500	Capsule: (Cinnamomum cassia) + Sulfonylurea derivatives or thiazolidinediones with or without metformin or metformin derivatives only or diet only/ Placebo (Wheat flour) + Sulfonylurea derivatives or thiazolidinediones with or without metformin or metformin derivatives only or diet only	Plasma Glucose, Plasma Insulin, HbA1c, TC, LDL, HDL, TG & HOMA-IR
Ziegenfuss et al. 2006[27]	USA	R, PC, DB	Pre-diabetic	22 (B)	12/10	12	Age: 46.3 ± 8.8 / 45.6 ± 11.1 BMI: 32.3 ± 5.7/ 34.4 ± 12.6	500	Capsule: Cinnulin PF® (Water-soluble cinnamon extract)/Placebo	BUN, ALP, AST, ALT Cholesterol, TG, HDL, VLDL, LDL, FBG, SBP & % fat
Blevins et al. 2007[28]	USA	R, PC	T2DM	57 (B)	29/28	12	Age: 63.6/ 58 BMI: 32.5 ± 1.7/ 32 ± 1.5	1000	Capsule: Cinnamon (C. cassia)/ Placebo (Wheat flour)	BMI, Glucose, HbA1c, TC, HDL, LDL, TG & Insulin
Crawford et al. 2009[29]	USA	R, SB	T2DM	109 (B)	55/54	12	Age: 60.5 ± 10.7/ 59.9 ± 9.2 BMI: 31.9 ± 6.4/ 32.9 ± 6.4	1000	Capsule: Cinnamomum cassia + Usual care with management changes / Usual care with management changes	HbA1c
Roussel et al. 2009[30]	USA	R, PC, DB	Impaired fasting glucose	21 (B)	11/10	12	Age: 45.8 ± 3.6/ 45.6 ± 2.7 BMI: 25 to 45/ 25 to 45	500	Capsule: Dried aqueous extract of Cinnamomon cassia (Cinnulin PF)/Placebo	Plasma MDA, Fasting Glucose & Fasting Insulin
Soni et al. 2009[31]	India	R	T2DM	30 (M)	15/15	6	Age: 40–60/ 40–60 BMI: NR	2000	Capsule: Cinnamon (Cinnamomum Cassia)/No supplement	FBG & PBG
Akilen et al. 2010[32]	UK	R, PC, DB	T2DM	58 (B)	30/28	12	Age: 54.90 ± 10.14/ 54.43 ± 12.53 BMI: 33.36 ± 4.20/ 32.13 ± 8.31	2000	Capsule: Cinnamon powder (Cinnamomum cassia)/ Placebo (Starch with 80% amylose and 20% amylopectin)	HbA1c, FPG, HDL, LDL, Serum TG, TC, Weight, WC, BMI, SBP & DBP
Khan et al. 2010[33]	Pakistan	R, PC	T2DM	14 (B)	7/7	4	Age: 40 ≤/ 40 ≤  BMI: NR	1500	Capsule: Cinnamon/ placebo (Maize flour)	Fasting serum glucose, Fasting serum TG, Fasting serum cholesterol, Fasting serum HDL & Fasting serum LDL
Haghighian et al. 2011 [34]	Iran	R, PC, DB	T2DM	60 (B)	30/30	8	Age: 59.1 ± 12.1/ 54.6 ± 13.1 BMI: 29 ± 3/ 29 ± 7	1500	Capsule: Whole cinnamon +  Usual diabetic medicine / Placebo +  Usual diabetic medicine	Weight, BMI, FBG, TC, TG, LDL & HDL
Wainstein et al. 2011 [35]	Israel	R, PC	T2DM	59 (B)	29/30	12	Age: 61.7 ± 6.3/ 64.4 ± 15.4 BMI: 29.8 ± 4.3/ 30.9 ± 6.9	1200	Capsule: Cinnamon (C. cassia) + Metformin and/or sulfonylurea and lifestyle interventions/ Placebo (Microcrystalline cellulose) + Metformin and/or sulfonylurea and lifestyle interventions	Weight, BMI, WC, FPG, FPI, HbA1c, Adiponectin, SBP, DBP, Pulse, TC, HDL, LDL, TG
Khan et al. 2012[36]	Pakistan	R, PC	T2DM	14 (B)	7/7	4	Age: 40 ≤/ 40 ≤  BMI: NR	1500	Capsule: Cinnamon (Cinnamomum Cassia)/ Placebo (Maize flour)	ALT, ALP, Bilirubin & Creatinine
Lu et al. 2012 [37]	China	R, PC, DB	T2DM	66 (B)	23/10		Age: 62.4 ± 7.9/ 60 ± 5.9 BMI: NR	120	Tablet: Cinnamon extract (Cinnamomum aromaticum) +  Gliclazide (diamicron, 30 mg per tablet) / Placebo + Gliclazide (diamicron, 30 mg per tablet)	HbA1c, Fasting glucose, TG, TC, HDL, LDL, AST & ALT
					23/10		Age: 58.9 ± 6.4/ 60 ± 5.9 BMI: NR	360
Sharma et al. 2012[38]	India	R, PC, DB	T2DM	150 (B)	50/25	12	Age: 30 ≤/30 ≤  BMI: 25.86 ± 3.93/ 27.34 ± 38.96	3000	Cinnamon/ Placebo	FBS, HbA1c, TC, TG, LDL, HDL
					50/25		Age: 30 ≤/30 ≤  BMI: 26.53 ± 4.53/27.34 ± 38.96	6000
Vafa et al. 2012 [39]	Iran	R, PC, DB	T2DM	37 (B)	19/18	8	Age: 54.11 ± 10.37/ 55.67 ± 7.98 BMI: 29.23 ± 3.98/ 28.59 ± 3.54	3000	Capsule: Cinnamon (Cinnamomum Zeylanicum) + Metformin: 1–1/5 gr/d, Gliclazide: 160–240 mg/d/ Placebo (Wheat flour) + Metformin: 1–1/5 gr/d, Gliclazide: 160–240 mg/d	FPG, Insulin, HbA1c, TG, TC, LDL, HDL, Apo A-1, Apo B, Weight, BMI, Fat body mass, DBP & SBP
Aldallal et al. 2013[40]	Iraq	R, PC	T2DM	48 (M)	8/9	12	Age: 43.6 ± 2.6/ 43.6 ± 2.6 BMI: 27.3 ± 1.7/ 27.3 ± 1.7	1000	Capsule: Cinnamon/ Placebo (wheat flour)	FBG, PBG, HbA1c, BUN, AST, ALT & ALP
					8/8		Age: 43.6 ± 2.6/ 43.6 ± 2.6 BMI: 27.3 ± 1.7/ 27.3 ± 1.7	2000
					7/8		Age: 43.6 ± 2.6/ 43.6 ± 2.6 BMI: 27.3 ± 1.7/ 27.3 ± 1.7	4000
Hasanzade et al. 2013 [41]	Iran	R, PC, DB	T2DM	71 (B)	35/36	8	Age: 53.7 ± 9.7/ 54.7 ± 8.1 BMI: 27.1 ± 3.2/ 28.7 ± 4	1000	Capsule: Cinnamon (Cinnamomum cassia)/Placebo	FBS & HbA1c
Zahmatkesh et al. 2013 [42]	Iran	R, PC, DB	T2DM	56 (B)	28/28	6	Age: 56.1 ± 9.8/ 53.1 ± 8.4 BMI: 29.6.3 ± 4/ 30.7 ± 3.3	2000	Capsule: Cinnamon +  diet or edible antidiabetes drugs / Placebo (Pea flour) +  diet or edible antidiabetes drugs	HbA1c, FBS, Cholesterol, TG, HDL & LDL
Askari et al. 2014 [43]	Iran	R, PC, DB	NAFLD	45 (B)	23/22	12	Age: 20–65/ 20–65 BMI: 29.9 ± 3.9/ 30.3 ± 4.1	1500	Capsule: Cinnamon/ Placebo (wheat flour)	BMI, WC, FBS, QUICK-I, HOMA, Cholesterol, LDL, HDL, TG, ALT, AST, GGT & hs-CRP
Azimi et al. 2014 [44]	Iran	R, PC, SB	T2DM	79 (B)	40/39	8	Age: 54.15 ± 6.32/ 53.64 ± 8.11 BMI: 28.78 ± 1.26/ 28.40 ± 1.24	3000	Sticks: Cinnamon (Cinnamomum verum) + 3 glasses of black tea/Placebo (3 glasses of black tea)	Weight, BMI, WC, F2-Isoprostan, hs-CRP, FBS, Insulin, HbA1c, Cholesterol, TG, LDL & HDL
Hosseini et al. 2014[45]	Iran	R, PC, DB	T2DM	47 (B)	24/23	8	Age: 52 ± 6.87/ 52 ± 5.8 BMI: NR	3000	Capsule: Cinnamon / Placebo (wheat flour)	FBS, TG, TC, LDL, VLDL, HDL
Kort et al. 2014 [46]	USA	R, PC, DB	PCOS	17 (F)	11/6	24	Age: 26.95 ± 4/ 27.86 ± 5 BMI: 33.0 ± 5.6/ 31.4 ± 6.0	1500	Capsule: Cinnamon/ Placebo	HOMA-IR, QUICK-I
Wickenberg et al. 2014 [47]	Sweden	R, PC, DB	IGT	17 (B)	9/8	12	Age: 73 ± 2/ 72 ± 2 BMI: 25.7 ± 1.3/ 28.6 ± 1.9	12,000	Capsule: Cinnamon (C. cassia)/ Placebo (cellulose)	Fasting glucose, Fasting insulin, HbA1c, Cholesterol, LDL, HDL, TG, AST, ALT & ALP
Tangvarasittichai et al. 2015 [48]	Thailand	R, PC, DB	T2DM	106 (B)	49/57	8	Age: 57.5 ± 1.1/ 56.9 ± 1.2 BMI: 24.73 ± 4.04/ 24.87 ± 3.72	1500	Capsule: Cinnamon (Cinnamomum cassia) +  Metformin, sulphonyleuraes or both / Placebo +  Metformin, sulphonyleuraes or both	Glucose, Insulin, HOMA-IR, QUICK-I, MDA, TAC, hs-CRP
Anderson et al. 2016 [49]	China	R, PC, DB	Prediabetic	137 (B)	64/73	8	Age: 61.3 ± 0.8/ 61.3 ± 0.8 BMI: 24.8 ± 0.4/ 25.8 ± 0.3	500	Capsule: Dried water extract of cinnamon (Cinnamomum cassia)/ Placebo (Dark broen (baked) wheat flour)	BMI, Fasting glucose, 2-h Glucose, Fasting Insulin, 2-h Insulin, HOMA-IR, SBP, DBP, TC, TG, LDL & HDL
Azimi et al. 2016 [50]	Iran	R, PC, SB	T2DM	79 (B)	40/39	8	Age: 54.15 ± 6.32/ 53.64 ± 8.11 BMI: 28.78 ± 1.26/ 28.40 ± 1.24	3000	Powder: Cinnamon (Cinnamomum verum) + 3 glasses of Black tea/ Placebo (3 glasses of Black tea)	Weight, BMI, Waist, sICAM-1, SBP & DBP
Mirfeizi et al 2016 [51]	Iran	R, PC, TB	T2DM	72 (B)	27/45	12	Age: 52 ± 13/ 54 ± 12 BMI: 28.36 ± 3.27/ 28.94 ± 4.45	1000	Capsule: Cinnamon/ Placebo (Starch)	BMI, FBG, 2-h PPG, HbA1c, Serum Insulin, HOMA-IR, TG, Cholesterol, LDL & HDL
Sengsuk et al. 2016[52]	Thailand	R, PC, DB	T2DM	99 (B)	49/50	8	Age: 57.2 ± 1.1/ 56.9 ± 1.2 BMI: 24.73 ± 4.04/ 24.86 ± 3.74	1500	Capsule: (Cinnamomum cassia)/ Placebo	SBP, DBP, Glucose, BUN, Creatinine, TC, TG, HDL, LDL & HbA1c
Gupta Jain et al. 2017 [53]	India	R, PC, DB	MetS	116 (B)	58/58	16	Age: 44.3 ± 7.2/ 45.1 ± 8.4 BMI: 33.6 ± 5.4/ 31.2 ± 4.4	3000	Capsule: Cinnamon/ Placebo (Wheat flour)	Weight, BMI, WC, WHR, %BF, SBP, DBP, FBG, HbA1c, PPG, TC, Serum TG, HDL, LDL & hs-CRP
Talaei et al. 2017 [54]	Iran	R, PC, DB	T2DM	39 (B)	20/19	8	Age: 58.90 ± 7.93/ 56.26 ± 9.46 BMI: 26.41 ± 3.06/ 29.02 ± 5.53	3000	Capsule: Cinnamon (Cinnamomum zeylanicum Blume) + Metformin/ Placebo (Microcrystalline cellulose) + Metformin	FBG, FI, HOMA-IR, HbA1c, TAC & MDA
Borzoei et al. 2018 [55]	Iran	R, PC, DB	PCOS	84 (F)	42/42	8	Age: 29.3 ± 6.14/ 30.2 ± 6.69 BMI: 30.7 ± 5.04/ 31.61 ± 4.84	1500	Capsule: Cinnamon/ Placebo (wheat flour)	Weight, BMI, Glucose, Insulin, HOMA-IR, Adiponectin, TC, TG, LDL & HDL
Borzoei et al. 2018 [56]	Iran	R, PC, DB	PCOS	84 (F)	42/42	8	Age: 29.26 ± 6.14 / 30.17 ± 6.69 BMI: 30.75 ± 5.04/ 31.61 ± 4.84	1500	Capsule: Cinnamon/ Placebo (Wheat flour)	BMI, TAC & MDA
Hajimonfarednejad et al. 2018 [57]	Iran	R, PC, DB	PCOS	59 (F)	29/30	12	Age: 28.62 ± 5.74/ 26.53 ± 6.35 BMI: 27.63 ± 4.30/ 26.09 ± 4.56	1500	Capsule: Cinnamon/ Placebo (450 mg of starch & 50 mg of cinnamon powder)	Weight, BMI, WC, FBS, Insulin, 2 h PPG, HOMA‐IR, HbA1C, TG, TC, LDL & HDL
Pishdad et al. 2018 [58]	Iran	R, PC, DB	Dyslipidemia	60 (F)	30/30	8	Age: 30–59/ 30–59 BMI: 31.25 ± 2/ 30.2 ± 4	3000	Capsule: Cinnamomum Verum/ Placebo (Microcrystalline cellulose)	Weight, BMI, WC, HDL, TC & TG
Shishehbor et al. 2018 [59]	Iran	R, PC, DB	RA	36 (F)	18/18	8	Age: 44.66 ± 11.22/ 49.11 ± 7.45 BMI: 28.59 ± 5.56/ 29.59 ± 5.43	2000	Capsule: Cinnamon/ Placebo (Starch)	Weight, BMI, CRP, TNF- α, ESR, SBP, DBP, FBS, TG, TC, HDL, LDL, ALT, AST
Mirmiran et al. 2019 [60]	Iran	R, PC, DB	T2DM	39 (B)	20/19	8	Age: 58.90 ± 7.93/ 56.26 ± 9.46 BMI: 26.41 ± 3.06/ 29.02 ± 5.53	3000	Capsule: Cinnamon extract/ Placebo (Microcrystalline cellulose)	FBG, HbA1c, TAC, FI, HOMA-IR, MDA, ICAM-1& VCAM-1
Zare et al. 2019 [61]	Iran	R, PC, TB	T2DM	138 (B)	69/69	12	Age: 52.1 ± 9.7/ 53.2 ± 8.5 BMI: 29.9 ± 12.3/ 29.3 ± 17.1	1000	Capsule: Cinnamon (Cinnamomum verum)/ Placebo (Starch)	BMI, Weight, %BF, Body muscle, Visceral fat, FPG, 2 h PPG, HbA1c, Insulin, HOMA-IR, TG, TC, LDL & HDL
Davari et al. 2020 [62]	Iran	R, PC, DB	T2DM	39 (B)	20/19	8	Age: 58.9 ± 7.93/ 56.26 ± 9.46 BMI: 26.41 ± 3.06/ 29.02 ± 5.53	3000	Capsule: Cinnamon extract/ Placebo (Microcrystalline cellulose)	FBS, FI, HbA1c, HOMA-IR, hs-CRP, TNF-α, IL-6
Romeo et al. 2020 [63]	Korea	R, PC, DB	Prediabetic	54 (B)	27/27	12	Age: 50.4 ± 11.5/ 54.1 ± 8 BMI: 28.2 ± 5.0/ 25.5 ± 3.3	1500	Capsule: Cinnamon extract/ Placebo (cellulose (91.5%), caramel food coloring (8.4%), and cinnamon incense (0.1%) did not contain any active substances)	FPG, Glycated albumin, HbA1c, Insulin, HOMA-IR & HOMA-B
Zare et al. 2020 [64]	Iran	R, PC, TB	T2DM	138 (B)	69/69	12	Age: 52.17 ± 9.7/53.2 ± 8.5 BMI: 29.92 ± 102.17/ 29.33 ± 142.12	1000	Capsule: Cinnamon/ Placebo (Starch)	FBG, HbA1c, Insulin & HOMA-IR
Zareie et al. 2020 [65]	Iran	R, PC, DB	Migraine	43 (B)	21/22	8	Age: 37.13 ± 7.8/ 39.36 ± 6.87 BMI: NR	1800	Capsule: Cinnamon/ Placebo (100 mg of corn starch)	IL-6
Delaviz et al. 2021 [66]	Iran	RCT	Progressive-relapsing MS	41 (B)	21/20	8	Age: 44.22 ± 11.8/ 42.94 ± 9.55 BMI: 26.03 ± 4.16/ 24.54 ± 4.55	2000	Capsule: Cinnamon, Placebo (Wheat flour)	BMI, WC, Weight, IL-6 & hs-CRP
Neto et al. 2021 [67]	Brazil	R, PC, TB	T2DM	140 (B)	71/69	12	Age: 61.7 ± 11.7/ 60.8 ± 10.8 BMI: NR	3000	Capsule: Cinnamon (Cinnamomum verum)/ Placebo (750 mg of microcrystalline cellulose)	HbA1c, Fasting venous glycemia, HOMA-IR & Insulin
Shirzad et al. 2021 [68]	Iran	R, PC, DB	Stage 1 HTN	37 (B)	19/18	12	Age: 54.4 ± 10.2/ 49.8 ± 9.07 BMI: 28.4 ± 3.52/ 26.4 ± 3.02	1500	Capsule: Cinnamon (Cinnamomum zeylanicum)/ Placebo (containing 500 mg lactose powder)	SBP, DBP, BMI, LDL, HDL, TG, TC & FBS
Dastgheib et al. 2022 [69]	Iran	R, PC, DB	PCOS	42 (F)	20/22	8	Age: 30.2 ± 5.72/ 30 ± 6.37 BMI: 28.61 ± 4.65/ 27.52 ± 5.09	1500	Capsule: Cinnamon (Cinnamomum zeylanicum extract)/ Placebo (rice flour capsule)	Weight, BMI, WC, WHR, FBS, Insulin, HOMA-IR, TG, TC, LDL & HDL
Al Dhaheri et al. 2024[70]	UAE	R, PC, DB	MetS	47 (B)	25/22	12	Age: 27.84 ± 12.04/ 28.82 ± 11.7 BMI: 33.53 ± 9.96/ 33.94 ± 5.84	3000	Powder: Cinnamon (Cinnamomum)/ Placebo	SBP, DBP, TC, TG, HDL, LDL, FBG, HbA1c, Weight, BMI, WC, WHR, Fat mass, %BF & Fat-free mass
Peivandi et al. 2024[71]	Iran	R, PC, DB	PCOS	39 (F)	19/20	24	Age: 18–38/ 18–38 BMI: 28.34 ± 3.77/ 30.31 ± 5.56	1500	Capsule: Cinnamon/ Placebo (Starch)	BMI, WC, HC, TG, HDL, HOMA-IR & QUICK-I
Zareie, 2024 [72]	Iran	R, PC, DB	Migraine	43 (B)	21/22	8	Age: 37.13 ± 7.6/ 39.36 ± 6.85 BMI: 26.12 ± 15.35/ 26.87 ± 22.37	600	Capsule: Cinnamon powder/ Placebo (100mg of corn starch)	Weight, BMI, WC, HC & WHR

Footprint: B, Both Sex; BMI, Body Mass Index; CON, Control Group; DB, Double-Blinded; DBP, Diastolic Blood Pressure; F, Female; FBS, Fasting Blood Sugar; HbA1c, Hemoglobin A1C; HDL, High-Density Lipoprotein; HC, Hip Circumference; HOMA-IR, Homeostatic Model Assessment of Insulin Resistance; hs-CRP, High-Sensitivity C-Reactive Protein; INT, Intervention Group; LDL, Low-Density Lipoprotein; MDA, Malondialdehyde; MetS, Metabolic Syndrome; NAFLD, Non-Alcoholic Fatty Liver Disease; PCOS, Polycystic Ovary Syndrome; QUICKI, Quantitative Insulin Sensitivity Check Index; RCT, Randomized Controlled Trial; SBP, Systolic Blood Pressure; T2DM, Type 2 Diabetes Mellitus; TC, Total Cholesterol; TG, Triglycerides; TB, Triple-Blinded; WC, Waist Circumference; WHR, Waist-to-Hip Ratio; BUN, Blood Urea Nitrogen; ALP, Alkaline Phosphatase; AST, Aspartate Aminotransferase; ALT, Alanine Aminotransferase; VLDL, Very-Low-Density Lipoprotein; FBG, Fasting Blood Glucose; FPG, Fasting Plasma Glucose; PBG, Postprandial Blood Glucose; FPI, Fasting Plasma Insulin; Apo A-1, Apolipoprotein A-I; Apo B, Apolipoprotein B; IGT, Impaired Glucose Tolerance; GGT, Gamma-Glutamyl Transferase; TAC, Total Antioxidant Capacity; 2 h PPG, 2 h Postprandial Glucose; sICAM-1, Soluble intercellular adhesion molecule-1; FI; Fasting Insulin; TNF- α, Tumor Necrosis Factor alpha; ESR, Erythrocyte Sedimentation Rate; %BF, Body Fat Percentage; VCAM-1, Vascular cell adhesion protein 1; RA, Rheumatoid Arthritis; MS, Multiple Sclerosis; HTN, Hypertension

The studies were published between 2003 [24] and 2024 [70–72] and were conducted in Pakistan [24, 33, 36], Germany [25], the Netherlands [26], the USA [27–30, 46], India [31, 38, 53], the UK [32], Israel [35], China [37, 49], Iran [34, 39, 41–45, 50, 51, 54–62, 64–66, 68, 69, 71, 72], Iraq [40], Sweden [47], Thailand [48, 52], Korea [63], Brazil [67], and the UAE [70]. Participants in the intervention groups had a mean age ranging from 18 to 73 years. Cinnamon doses varied from 120 mg/day to 12,000 mg/day, with intervention durations ranging from 4 to 24 weeks. Intervention group sample sizes ranged from 7 to 100 participants. Nine studies included only female participants [26, 46, 55–59, 69, 71], two included only males [31, 40], and the remainder included both genders. The populations studied included individuals with T2DM [24–26, 28, 29, 31–42, 44, 45, 48, 50–52, 54, 60–62, 64, 67], prediabetes [27, 49, 63], impaired fasting glucose [30], non-alcoholic fatty liver disease (NAFLD) [43], polycystic ovary syndrome (PCOS) [46, 55–57, 69, 71], impaired glucose tolerance (IGT) [47], metabolic syndrome (MetS) [53, 70], dyslipidemia [58], rheumatoid arthritis (RA) [59], migraine [65, 72], progressive relapsing multiple sclerosis (MS) [66], and stage 1 HTN [68].

Qualitative data assessment

Using the Cochrane Risk of Bias Assessment tool, 43 studies were rated as high risk of bias [24–47, 49–51, 54, 55, 58–66, 68–72], five as moderate risk [32, 52, 53, 57, 67], and one study as low risk [48] (Table 2).

Table 2.

Quality of included studies in the meta-analysis

Study, Year (Ref.)	Random sequence generation	Allocation concealment	Blinding of participants & personnel	Blinding of outcome assessment	Incomplete outcome data	Selective outcome reporting	Other sources of bias	Overall quality
Khan, 2003[24]	L	H	H	H	U	L	L	Poor
Mang, 2006[25]	U	H	L	H	H	L	L	Poor
Vanschoonbeek, 2006[26]	H	H	L	H	L	L	L	Poor
Ziegenfuss, 2006[27]	U	H	L	H	L	L	L	Poor
Blevins, 2007[28]	U	H	H	H	H	L	L	Poor
Crawford, 2009[29]	L	L	H	H	H	L	L	Poor
Roussel, 2009[30]	U	H	U	H	L	L	L	Poor
Soni, 2009[31]	H	H	H	H	L	L	L	Poor
Akilen, 2010[32]	L	L	L	H	L	L	L	Fair
Khan, 2010[33]	U	H	H	H	L	L	L	Poor
Haghighian, 2011 [34]	U	H	U	H	U	L	L	Poor
Wainstein, 2011 [35]	L	H	L	H	L	L	L	Poor
Khan, 2012[36]	L	H	H	H	L	L	L	Poor
Lu, 2012 [37]	U	H	L	H	L	L	L	Poor
Sharma, 2012[38]	U	H	L	H	L	L	L	Poor
Vafa, 2012 [39]	U	H	L	H	H	L	L	Poor
Aldallal, 2013[40]	L	H	L	H	H	L	L	Poor
Hasanzade, 2013 [41]	L	H	L	H	L	L	L	Poor
Zahmatkesh, 2013 [42]	L	H	U	H	H	L	L	Poor
Askari, 2014 [43]	L	H	L	H	L	L	L	Poor
Azimi, 2014 [44]	L	H	H	H	L	L	L	Poor
Hosseini, 2014[45]	U	H	L	H	L	L	L	Poor
Kort, 2014 [46]	L	H	L	H	L	L	L	Poor
Wickenberg, 2014 [47]	L	L	U	H	H	L	L	Poor
Tangvarasittichai, 2015 [48]	L	L	L	L	L	L	L	Good
Anderson, 2016 [49]	L	H	L	H	H	L	L	Poor
Azimi, 2016 [50]	L	H	L	H	L	L	L	Poor
Mirfeizi, 2016 [51]	U	H	L	U	L	L	L	Poor
Sengsuk, 2016[52]	L	H	L	L	L	L	L	Fair
Gupta Jain, 2017 [53]	L	L	L	H	L	L	L	Fair
Talaei, 2017 [54]	U	H	L	H	H	L	L	Poor
Borzoei, 2018 [55]	L	H	U	H	L	L	L	Poor
Borzoei, 2018 [56]	L	H	U	H	L	L	L	Poor
Hajimonfarednejad, 2018 [57]	L	H	L	L	L	L	L	Fair
Pishdad, 2018 [58]	L	H	U	H	L	L	L	Poor
Shishehbor, 2018 [59]	L	H	L	H	L	L	L	Poor
Mirmiran, 2019 [60]	L	H	L	H	H	L	L	Poor
Zare, 2019 [61]	L	H	U	U	L	L	L	Poor
Davari, 2020 [62]	U	H	L	H	H	L	L	Poor
Romeo, 2020 [63]	L	H	L	H	L	L	L	Poor
Zare, 2020 [64]	L	H	U	U	L	L	L	Poor
Zareie, 2020 [65]	L	H	L	H	H	L	L	Poor
Delaviz, 2021 [66]	L	H	L	H	H	L	L	Poor
Neto, 2021 143]	L	H	L	L	L	L	L	Fair
Shirzad, 2021 [68]	L	H	L	H	L	L	L	Poor
Dastgheib, 2022 [69]	L	H	L	H	H	L	L	Poor
Al Dhaheri, 2024[70]	L	H	H	H	H	L	L	Poor
Peivandi, 2024[71]	L	H	L	L	H	L	L	Poor
Zareie, 2024 [148)	L	H	L	H	H	L	L	Poor

Footprint: H, high risk of bias; L, low risk of bias; U, unclear risk of bias

Effects of cinnamon supplementation on anthropometric indices

Cinnamon supplementation resulted in a statistically significant reduction in WC (SMD = − 0.40; 95% CI: − 0.73, − 0.06; P = 0.020; I² = 80.5%, P < 0.001). However, no significant effect was observed for BF (SMD = − 0.19; 95% CI: − 0.88, 0.50; P = 0.590; I² = 88.9%, P < 0.001), BMI (SMD = − 0.13; 95% CI: − 0.40, 0.13; P = 0.320; I² = 83.8%, P < 0.001), weight (SMD = − 0.08; 95% CI: − 0.41, 0.25; P = 0.629; I² = 85.3%, P < 0.001), and WHR (SMD = − 0.28; 95% CI: − 0.61, 0.06; P = 0.102; I² = 37.8%, P = 0.185) (Supplementary Fig. 1).

Sensitivity analyses for BMI, WC, and WHR indicated stable results upon exclusion of individual studies. However, removing Al Daheri et al. [70] significantly affected BF (SMD = − 0.56; 95% CI: − 0.95, − 0.17), and excluding Pishdad et al. [58] impacted the findings for weight (SMD = − 0.25; 95% CI: − 0.46, − 0.03). Publication bias was not detected for BF (Egger’s P = 0.460), BMI (Egger’s P = 0.345), WC (Egger’s P = 0.233), and weight (Egger’s P = 0.065), though significant asymmetry was found for WHR (Egger’s P = 0.045).

Effects of cinnamon supplementation on blood pressure

Studies indicated that cinnamon supplementation led to a significant decrease in diastolic blood pressure (DBP) (SMD = − 1.04; 95% CI: − 1.54, − 0.55; P < 0.001; I² = 88.6%, P < 0.001) and systolic blood pressure (SBP) (SMD = − 0.85; 95% CI: − 1.54, − 0.16; P = 0.016; I² = 94.3%, P < 0.001) (Supplementary Fig. 2).

Sensitivity analyses for DBP confirmed stable outcomes, while excluding Al Daheri et al. [70] significantly altered the SBP results (SMD: − 0.61; 95% CI: − 1.27, 0.04). No publication bias was detected for DBP (Egger's P = 0.803) or SBP (Egger's P = 0.357).

Effects of cinnamon supplementation on glycemic profile

Cinnamon supplementation demonstrated a significant effect on fasting glucose (SMD = − 1.28; 95% CI: − 1.65, − 0.90; P < 0.001; I² = 93.5%, P < 0.001), fasting insulin (SMD = − 0.26; 95% CI: − 0.50, − 0.02; P = 0.035; I² = 78.0%, P < 0.001), HbA1c (SMD = − 0.71; 95% CI: − 1.02, − 0.40; P < 0.001; I² = 89.3%, P < 0.001), HOMA-IR (SMD = − 0.54; 95% CI: − 0.82, − 0.26; P < 0.001; I² = 80.4%, P < 0.001) and postprandial blood glucose (SMD = − 2.28; 95% CI: − 3.48, − 1.08; P < 0.001; I² = 94.4%, P < 0.001). Nevertheless, trials showed no significant impact on the QUICKI (SMD = − 0.33; 95% CI: − 0.72, 0.07; P = 0.103; I² = 24.0%, P = 0.268) (Supplementary Fig. 3).

Sensitivity analyses across fasting glucose, fasting insulin, HbA1c, HOMA-IR, and postprandial glucose indicated stable results. However, removing Peivandi et al. [71] notably changed the QUICKI results (SMD = − 0.50; 95% CI: − 0.86, − 0.14). Publication bias was absent for fasting insulin (Egger's P = 0.131), HbA1c (Egger's P = 0.096), HOMA-IR (Egger's P = 0.135) and QUICKI (Egger's P = 0.392), though significant asymmetry was noted for fasting glucose (Egger's P < 0.001) and postprandial glucose (Egger's P < 0.001).

Effects of cinnamon supplementation on inflammatory biomarkers

Studies assessed CRP levels, demonstrating a significant reduction (SMD = − 0.78; 95% CI: − 1.28, − 0.27; P = 0.003; I² = 84.3%, P < 0.001). For IL-6, three studies reported no significant reduction (SMD = − 0.37; 95% CI: − 0.90, 0.16; P = 0.168; I² = 53.1%, P = 0.119) (Supplementary Fig. 4).

Sensitivity analyses for both CRP and IL-6 confirmed the stability of these findings across different study exclusions. No publication bias was detected for CRP (Egger’s P = 0.275) or IL-6 (Egger’s P = 0.438).

Effects of cinnamon supplementation on lipid profile

Cinnamon supplementation had a significant effect on lipid profile indices including, HDL-C (SMD = 0.56; 95% CI: 0.23, 0.89; P = 0.001; I² = 90.6%, P < 0.001), LDL-C (SMD = − 0.71; 95% CI: − 1.02, − 0.40; P < 0.001; I² = 88.9%, P < 0.001), TC (SMD = − 1.15; 95% CI: − 1.55, − 0.75; P < 0.001; I² = 93.1%, P < 0.001) and TG (SMD = − 0.91; 95% CI: − 1.25, − 0.56; P < 0.001; I² = 91.3%, P < 0.001) (Supplementary Fig. 5).

Sensitivity analyses for these lipid parameters confirmed the robustness of these results, with no detected publication bias for HDL-C (Egger’s P = 0.056). However, significant asymmetry was observed for LDL (Egger’s P = 0.022), TC (Egger’s P < 0.001) and TG (Egger’s P = 0.001).

Effects of cinnamon supplementation on liver function tests

Our finding revealed that cinnamon had no considerable impact on ALP (SMD = − 0.07; 95% CI: − 0.47, 0.32; P = 0.720; I² = 0.0%, P = 0.488), ALT (SMD = − 0.59; 95% CI: − 1.45, 0.28; P = 0.182; I² = 88.9%, P < 0.001), AST (SMD = − 0.29; 95% CI: − 0.96, 0.39; P = 0.406; I² = 82.4%, P < 0.001), and BUN (SMD = − 0.50; 95% CI: − 1.74, 0.74; P = 0.428; I² = 90.0%, P < 0.001) (Supplementary Fig. 6).

Sensitivity analyses for ALP, ALT, and BUN showed that excluding any studies did not alter overall results, although excluding Shishehbor et al. [59] significantly impacted ALT (SMD = − 0.84; 95% CI: − 1.59, − 0.08). Publication bias was not detected for ALT (Egger’s P = 0.314), AST (Egger’s P = 0.989), or BUN (Egger’s P = 0.371); however, asymmetry was noted for ALP (Egger’s P = 0.028).

Effects of cinnamon supplementation on oxidative stress parameters

Studies on MDA indicated a significant reduction (SMD = − 0.76; 95% CI: − 1.07, − 0.45; P < 0.001; I² = 34.3%%, P = 0.193) (Supplementary Fig. 7). In contrast, no significant effect was reported for TAC (SMD = 0.52; 95% CI: − 0.05, 1.08; P = 0.073; I² = 79.1%%, P = 0.002) (Supplementary Fig. 7).

Sensitivity analysis for MDA confirmed the stability of these results. However, excluding studies by Talaei et al. (SMD = 0.71, 95% CI: 0.15, 1.27) [54] and Mirmiran et al. (SMD = 0.68, 95% CI: 0.07, 1.28) [60] significantly changed the effect on TAC. No publication bias was detected for MDA (Egger’s P = 0.904), though significant asymmetry was observed for TAC (Egger’s P = 0.008).

Subgroup analysis

Subgroup analysis based on health conditions (T2DM or prediabetes vs. other conditions: PCOS, NAFLD, MetS, dyslipidemia, HTN, MS, RA, migraine, IGT, and impaired fasting blood glucose), cinnamon dosage (> 2000 mg/day vs. ≤ 2000 mg/day), intervention duration (≥ 8 weeks vs. < 8 weeks), participant age (≥ 50 years vs. < 50 years), baseline BMI (Healthy/Overweight [< 30 kg/m²] vs. Obese [≥ 30 kg/m²]), cinnamon type (C. cassia vs. C. verum vs. C. zeylanicum), and continent (Asia vs. Europe or America) is presented in Table 3.

Table 3.

Description of the analysis and subgroup results of Cinnamon supplementation on cardiovascular disease risk factors

	StudiesN	ParticipantN	SMD (95%CI)	P-value	Heterogeneity
					P heterogeneity	I2	P between sub-groups
Analysis and subgroup results of Cinnamon supplementation on BF
Overall effect	5	360	− 0.19 (− 0.88, 0.50)	0.590	< 0.001	88.9%
Analysis and subgroup results of Cinnamon supplementation on BMI
Overall effect	23	1505	− 0.13 (− 0.40, 0.13)	0.320	< 0.001	83.8%
Health Condition
Prediabetes/Diabetes	10	772	− 0.28 (− 0.81, 0.25)	0.305	< 0.001	92.0%	0.394
Other conditions	13	733	− 0.03 (− 0.21, 0.15)	0.707	0.130	31.6%
Cinnamon dosage (mg/day)
2000 >	14	952	− 0.30 (− 0.65, 0.06)	0.099	< 0.001	85.5%	0.102
2000 ≤	9	553	0.12 (− 0.23, 0.48)	0.502	< 0.001	76.1%
Intervention duration (weeks)
8 ≥	12	778	− 0.07 (− 0.21, 0.07)	0.347	0.980	0.0%	0.760
8 <	11	727	− 0.16 (− 0.71, 0.40)	0.580	< 0.001	92.2%
Intervention Age (year)
50 ≥	12	696	− 0.04 (− 0.23, 0.15)	0.676	0.099	36.5%	0.449
50 <	11	809	− 0.25 (− 0.74, 0.25)	0.330	< 0.001	91.3%
Baseline BMI
Healthy/Overweight (< 30 kg/m2)	16	999	− 0.23 (− 0.52, 0.08)	0.142	< 0.001	81.4%	0.337
Obese (≥ 30 kg/m2)	7	506	0.07 (− 0.46, 0.60)	0.787	< 0.001	88.1%
Not given	–	–	–	–	–	–
Cinnamon type
C.cassia	3	174	− 0.03 (− 1.34, 1.29)	0.968	< 0.001	94.2%	0.657
C.verum	3	218	0.06 (− 0.21, 0.32)	0.674	0.995	0.0%
C.zeylanicum	3	116	− 0.17 (− 0.54, 0.20)	0.362	0.506	0.0%
Not given	14	997	− 0.19 (− 0.54, 0.16)	0.291	< 0.001	86.2%
Continent
Asia	21	1390	− 0.14 (− 0.39, 0.11)	0.262	< 0.001	80.2%	0.956
Europe/America	2	115	− 0.08 (− 2.42, 2.27)	0.950	< 0.001	97.1%
Analysis and subgroup results of Cinnamon supplementation on WC
Overall effect	13	767	− 0.40 (− 0.73, − 0.06)	0.020	< 0.001	80.5%
Health Condition
Prediabetes/Diabetes	4	275	− 0.09 (− 0.33, 0.15)	0.466	0.908	0.0%	0.090
Other conditions	9	492	− 0.56 (− 1.06, − 0.07)	0.026	< 0.001	85.3%
Cinnamon dosage (mg/day)
2000 >	6	287	− 0.09 (− 0.32, 0.15)	0.475	0.880	0.0%	0.047
2000 ≤	7	480	− 0.71 (− 1.28, − 0.14)	0.015	< 0.001	88.6%
Intervention duration (weeks)
8 ≥	6	344	− 0.19 (− 0.40, 0.02)	0.080	0.533	0.0%	0.225
8 <	7	423	− 0.59 (− 1.21, 0.02)	0.059	< 0.001	88.9%
Intervention Age (year)
50 ≥	9	492	− 0.56 (− 1.06, − 0.07)	0.026	< 0.001	85.3%	0.090
50 <	4	275	− 0.09 (− 0.33, 0.15)	0.466	0.908	0.0%
Baseline BMI
Healthy/Overweight (< 30 kg/m2)	9	486	− − 0.10 (− 0.28, 0.08)	0.273	0.855	0.0%	0.032
Obese (≥ 30 kg/m2)	4	281	− 1.16 (− 2.11, − 0.21)	0.017	< 0.001	92.1%
Not given	–	–	–	–	–	–
Cinnamon type
C.cassia	2	117	− 0.19 (− 0.55, 0.18)	0.315	0.806	0.0%	0.470
C.verum	3	218	− 0.15 (− 0.44, 0.14)	0.322	0.307	15.4%
C.zeylanicum	1	42	− 0.02 (− 0.62, 0.59)	0.958	–	–
Not given	7	390	− 0.67 (− 1.30, − 0.03)	0.041	< 0.001	88.4%
Continent
Asia	12	709	− 0.42 (− 0.78, − 0.05)	0.026	< 0.001	82.1%	0.568
Europe/America	1	58	− 0.23 (− 0.75, 0.28)	0.378	–	–
Analysis and subgroup results of Cinnamon supplementation on Weight
Overall effect	16	1038	− 0.08 (− 0.41, 0.25)	0.629	< 0.001	85.3%
Health Condition
Prediabetes/Diabetes	7	510	− 0.22 (− 0.65, 0.20)	0.297	< 0.001	81.7%	0.442
Other conditions	9	528	0.04 (− 0.48, 0.56)	0.887	< 0.001	87.9%
Cinnamon dosage (mg/day)
2000 >	7	485	− 0.22 (− 0.64, 0.20)	0.305	< 0.001	80.6%	0.456
2000 ≤	9	553	0.03 (− 0.48, 0.54)	0.905	< 0.001	88.1%
Intervention duration (weeks)
8 ≥	10	561	0.15 (− 0.28, 0.58)	0.490	< 0.001	83.9%	0.047
8 <	6	477	− 0.46 (− 0.87, − 0.04)	0.031	< 0.001	79.0%
Intervention Age (year)
50 ≥	9	528	0.04 (− 0.48, 0.56)	0.887	< 0.001	87.9%	0.442
50 <	7	510	− 0.22 (− 0.65, 0.20)	0.297	< 0.001	81.7%
Baseline BMI
Healthy/Overweight (< 30 kg/m2)	11	673	− 0.20 (− 0.49, 0.09)	0.168	< 0.001	70.2%	0.410
Obese (≥ 30 kg/m2)	5	365	0.20 (− 0.70, 1.09)	0.671	< 0.001	93.9%
Not given	–	–	–	–	–	–
Cinnamon type
C.cassia	2	117	− 0.06 (− 0.43, 0.30)	0.729	0.447	0.0%	0.340
C.verum	3	218	0.83 (− 0.57, 2.22)	0.245	< 0.001	95.5%
C.zeylanicum	2	79	− 0.27 (− 0.72, 0.17)	0.232	0.619	0.0%
Not given	9	624	− 0.33 (− 0.66, 0.01)	0.046	< 0.001	74.5%
Continent
Asia	15	980	− 0.07 (− 0.43, 0.28)	0.690	< 0.001	86.3%	0.673
Europe/America	1	58	− 0.21 (− 0.72, 0.31)	0.433	−	−
Analysis and subgroup results of Cinnamon supplementation on WHR
Overall effect	4	248	− 0.28 (− 0.61, 0.06)	0.102	0.185	37.8%
Analysis and subgroup results of Cinnamon supplementation on DBP
Overall effect	10	703	− 1.04 (− 1.54, − 0.55)	< 0.001	< 0.001	88.6%
Health Condition
Prediabetes/Diabetes	6	467	− 0.90 (− 1.54, − 0.25)	0.01	< 0.001	90.3%	0.461
Other conditions	4	236	− 1.27 (− 2.04, − 0.50)	< 0.001	< 0.001	84.4%
Cinnamon dosage (mg/day)
2000 >	4	330	− 0.64 (− 1.43, 0.14)	0.109	< 0.001	90.9%	0.169
2000 ≤	6	373	− 1.32 (− 1.88, − 0.76)	< 0.001	< 0.001	82.3%
Intervention duration (weeks)
8 ≥	5	386	− 1.24 (− 1.99, − 0.49)	0.001	< 0.001	90.4%	0.474
8 <	5	317	− 0.85 (− 1.59, − 0.12)	0.023	< 0.001	89.1%
Intervention Age (year)
50 ≥	3	199	− 1.71 (− 2.03, − 1.38)	< 0.001	0.785	0.0%	0.008
50 <	7	504	− 0.79 (− 1.38, − 0.20)	0.008	< 0.001	89.3%
Baseline BMI
Healthy/Overweight (< 30 kg/m2)	7	482	− 0.92 (− 1.55, − 0.29)	0.004	< 0.001	89.9%	0.392
Obese (≥ 30 kg/m2)	3	221	− 1.34 (− 2.08, − 0.60)	< 0.001	0.003	82.7%
Not given	–	–	–	–	–	–
Cinnamon type
C.cassia	2	117	− 0.37 (− 0.89, 0.15)	0.163	0.157	50.1%	< 0.001
C.verum	1	79	− 2.02 (− 2.57, − 1.48)	< 0.001	–	–
C.zeylanicum	2	74	− 0.19 (− 0.65, 0.27)	0.409	0.718	0.0%
Not given	5	433	− 1.44 (− 2.09, − 0.79)	< 0.001	< 0.001	88.3%
Continent
Asia	9	645	− 1.09 (− 1.63, − 0.55)	< 0.001	< 0.001	89.6%	0.246
Europe/America	1	58	− 0.64 (− 1.17, − 0.11)	0.018	–	–
Analysis and subgroup results of Cinnamon supplementation on SBP
Overall effect	11	725	− 0.85 (− 1.54, − 0.16)	0.016	< 0.001	94.3%
Health Condition
Prediabetes/Diabetes	7	489	− 0.47 (− 1.30, 0.37)	0.270	< 0.001	94.4%	0.137
Other conditions	4	236	− 1.53 (− 2.65, − 0.41)	0.007	< 0.001	91.8%
Cinnamon dosage (mg/day)
2000 >	5	352	− 0.81 (− 1.57, − 0.05)	0.037	< 0.001	90.2%	0.920
2000 ≤	6	373	− 0.88 (− 2.12, 0.36)	0.163	< 0.001	96.3%
Intervention duration (weeks)
8 ≥	5	386	− 0.29 (− 1.42, 0.84)	0.613	< 0.001	96.0%	0.142
8 <	6	339	− 1.32 (− 2.10, − 0.54)	0.001	< 0.001	89.6%
Intervention Age (year)
50 ≥	4	221	− 2.04 (− 2.89, − 1.19)	< 0.001	0.001	81.3%	0.002
50 <	7	504	− 0.20 (− 0.96, 0.55)	0.598	< 0.001	93.8%
Baseline BMI
Healthy/Overweight (< 30 kg/m2)	7	482	− 0.28 (− 1.08, 0.53)	0.500	< 0.001	94.1%	0.011
Obese (≥ 30 kg/m2)	4	243	− 1.88 (− 2.81, − 0.95)	< 0.001	< 0.001	87.4%
Not given	–	–	–	–	–	–
Cinnamon type
C.cassia	2	117	− 0.66 (− 1.03, − 0.29)	0.001	0.353	0.0%	< 0.001
C.verum	1	79	1.64 (1.13, 2.16)	< 0.001	–	–
C.zeylanicum	2	74	0.01 (− 0.45, 0.47)	0.970	0.970	0.0%
Not given	6	455	− 1.63 (− 2.48, − 0.78)	< 0.001	< 0.001	93.1%
Continent
Asia	9	645	− 0.73 (− 1.53, 0.07)	0.072	< 0.001	95.2%	0.377
Europe/America	2	80	− 1.40 (− 2.64, − 0.16)	0.027	0.036	77.3%
Analysis and subgroup results of Cinnamon supplementation on Fasting glucose
Overall effect	39	1998	− 1.45 (− 1.88, − 1.02)	< 0.001	< 0.001	93.8%
Health Condition
Prediabetes/Diabetes	30	1578	− 1.90 (− 2.43, − 1.37)	< 0.001	< 0.001	94.5%	< 0.001
Other conditions	9	420	− 0.34 (− 1.02, 0.35)	0.333	< 0.001	90.1%
Cinnamon dosage (mg/day)
2000 >	19	1072	− 0.86 (− 1.25, − 0.47)	< 0.001	< 0.001	87.5%	0.003
2000 ≤	20	926	− 2.28 (− 3.13, − 1.44)	< 0.001	< 0.001	95.9%
Intervention duration (weeks)
8 ≥	17	786	− 1.25 (− 1.81, − 0.69)	< 0.001	< 0.001	91.7%	0.356
8 <	22	1212	− 1.65 (− 2.29, − 1.01)	< 0.001	< 0.001	94.8%
Intervention Age (year)
50 ≥	15	630	− 4.01 (− 5.35, − 2.67)	< 0.001	< 0.001	96.6%	< 0.001
50 <	24	1368	− 0.68 (− 1.00, − 0.36)	< 0.001	< 0.001	86.6%
Baseline BMI
Healthy/Overweight (< 30 kg/m2)	26	1517	− 1.16 (− 1.69, − 0.63)	< 0.001	< 0.001	94.6%	0.094
Obese (≥ 30 kg/m2)	5	264	− 1.32 (− 2.07, − 0.57)	0.001	< 0.001	84.5%
Not given	8	217	− 2.68 (− 3.96, − 1.41)	< 0.001	< 0.001	91.4%
Cinnamon type
C.cassia	9	316	− 1.68 (− 2.83, − 0.54)	0.004	< 0.001	93.9%	< 0.001
C.verum	1	79	0.02 (− 0.42, 0.46)	0.935	–	–
C.zeylanicum	3	116	− 0.13 (− 0.56, 0.29)	0.541	0.262	25.3%
Not given	26	1487	− 1.68 (− 2.22, − 1.13)	< 0.001	< 0.001	94.4%
Continent
Asia	34	1815	− 1.67 (− 2.15, − 1.19)	< 0.001	< 0.001	94.3%	0.007
Europe/America	5	183	− 0.27 (− 1.16, 0.63)	0.559	< 0.001	85.7%
Analysis and subgroup results of Cinnamon supplementation on Fasting insulin
Overall effect	7	349	0.09 (− 0.22, 0.39)	0.582	0.095	44.3%
Analysis and subgroup results of Cinnamon supplementation on Glucose
Overall effect	5	371	− 0.39 (− 1.17, 0.40)	0.339	< 0.001	92.1%
Analysis and subgroup results of Cinnamon supplementation on HbA1c
Overall effect	30	1876	− 0.71 (− 1.02, − 0.40)	< 0.001	< 0.001	89.3%
Health Condition
Prediabetes/Diabetes	26	1637	− 0.63 (− 0.94, − 0.32)	< 0.001	< 0.001	87.6%	0.513
Other conditions	4	239	− 1.15 (− 2.65, 0.36)	0.135	< 0.001	95.5%
Cinnamon dosage (mg/day)
2000 >	14	964	− 0.49 (− 0.88, − 0.10)	0.013	< 0.001	87.0%	0.162
2000 ≤	16	912	− 0.95 (− 1.45, − 0.44)	< 0.001	< 0.001	91.2%
Intervention duration (weeks)
8 ≥	9	483	− 0.14 (− 0.50, 0.22)	0.434	< 0.001	73.4%	0.002
8 <	21	1393	− 1.02 (− 1.42, − 0.61)	< 0.001	< 0.001	91.0%
Intervention Age (year)
50 ≥	8	420	− 2.89 (− 4.00, − 1.77)	< 0.001	< 0.001	94.0%	< 0.001
50 <	22	1456	− 0.28 (− 0.51, − 0.05)	0.019	< 0.001	77.5%
Baseline BMI
Healthy/Overweight (< 30 kg/m2)	21	1258	− 0.70 (− 1.09, − 0.31)	< 0.001	< 0.001	89.6%	0.662
Obese (≥ 30 kg/m2)	6	412	− 0.87 (− 1.73, − 0.01)	0.047	< 0.001	93.6%
Not given	3	206	− 0.53 (− 0.82, − 0.25)	< 0.001	0.585	0.0%
Cinnamon type
C.cassia	7	396	0.05 (− 0.30, 0.40)	0.781	0.009		< 0.001
C.verum	1	79	− 0.08 (− 0.52, 0.36)	0.731	–	–
C.zeylanicum	1	37	− 0.50 (− 1.15, 0.16)	0.137	–	–
Not given	21	1364	− 1.07 (− 1.47, − 0.67)	< 0.001	< 0.001	90.5%
Continent
Asia	23	1405	− 0.96 (− 1.36, − 0.57)	< 0.001	< 0.001	90.7%	0.001
Europe/America	7	471	− 0.11 (− 0.44, 0.23)	0.530	0.008	65.2%
Analysis and subgroup results of Cinnamon supplementation on HOMA-IR
Overall effect	17	1211	− 0.54 (− 0.82, − 0.26)	< 0.001	< 0.001	80.4%
Health Condition
Prediabetes/Diabetes	11	925	− 0.44 (− 0.81, − 0.07)	0.019	< 0.001	85.8%	0.189
Other conditions	6	286	− 0.77 (− 1.10, − 0.44)	< 0.001	0.128	41.6%
Cinnamon dosage (mg/day)
2000 >	13	954	− 0.62 (− 0.96, − 0.28)	< 0.001	< 0.001	83.4%	0.172
2000 ≤	4	257	− 0.33 (− 0.58, − 0.08)	0.009	0.610	0.0%
Intervention duration (weeks)
8 ≥	8	509	− 0.45 (− 0.70, − 0.20)	< 0.001	0.086	43.9%	0.486
8 <	9	702	− 0.63 (− 1.09, − 0.17)	0.007	< 0.001	87.4%
Intervention Age (year)
50 ≥	6	286	− 0.77 (− 1.10, − 0.44)	< 0.001	0.128	41.6%	0.189
50 <	11	925	− 0.44 (− 0.81, − 0.07)	0.019	< 0.001	85.8%
Baseline BMI
Healthy/Overweight (< 30 kg/m2)	13	945	− 0.58 (− 0.91, − 0.24)	0.001	< 0.001	83.1%	0.817
Obese (≥ 30 kg/m2)	3	126	− 0.30 (− 1.23, 0.63)	0.527	0.008	79.4%
Not given	1	140	− 0.47 (− 0.81, − 0.14)	0.006	–	–
Cinnamon type
C.cassia	2	131	− 0.41 (− 1.00, 0.19)	0.183	0.154	50.8%	0.836
C.verum	–	–	–	–	–	–
C.zeylanicum	1	42	− 0.67 (− 1.29, − 0.05)	0.036	–	–
Not given	14	1038	− 0.55 (− 0.88, − 0.22)	0.001	< 0.001	83.6%
Continent
Asia	14	1029	− 0.62 (− 0.93, − 0.30)	< 0.001	< 0.001	82.3%	0.157
Europe/America	3	182	− 0.20 (− 0.68, 0.29)	0.420	0.192	39.4%
Analysis and subgroup results of Cinnamon supplementation on Insulin
Overall effect	13	1031	− 0.45 (− 0.74, − 0.15)	0.003	< 0.001	81.0%
Health Condition
Prediabetes/Diabetes	10	846	− 0.36 (− 0.72, 0.01)	0.058	< 0.001	84.7%	0.113
Other conditions	3	185	− 0.74 (− 1.04, − 0.44)	< 0.001	0.941	0.0%
Cinnamon dosage (mg/day)
2000 >	10	775	− 0.59 (− 0.92, − 0.26)	< 0.001	< 0.001	79.1%	0.004
2000 ≤	3	256	0.02 (− 0.22, 0.27)	0.852	0.974	0.0%
Intervention duration (weeks)
8 ≥	6	373	− 0.43 (− 0.81, − 0.06)	0.025	0.010	66.8%	0.908
8 <	7	658	− 0.47 (− 0.93, − 0.01)	0.047	< 0.001	87.5%
Intervention Age (year)
50 ≥	3	185	− 0.74 (− 1.04, − 0.44)	< 0.001	0.941	0.0%	0.113
50 <	10	846	− 0.36 (− 0.72, 0.01)	0.058	< 0.001	84.7%
Baseline BMI
Healthy/Overweight (< 30 kg/m2)	9	725	− 0.39 (− 0.71, − 0.07)	0.016	< 0.001	76.8%	0.072
Obese (≥ 30 kg/m2)	3	166	− 0.82 (− 1.72, 0.08)	0.075	0.001	85.1%
Not given	1	140	0.04 (− 0.29, 0.38)	0.797	–	–
Cinnamon type
C.cassia	3	188	− 0.88 (− 1.74, − 0.03)	0.044	0.002	84.4%	0.329
C.verum	1	79	− 0.02 (− 0.46, 0.42)	0.930	–	–
C.zeylanicum	2	79	− 0.40 (− 1.25, 0.45)	0.359	0.059	71.9%
Not given	7	685	− 0.35 (− 0.71, 0.01)	0.060	< 0.001	81.0%
Continent
Asia	10	809	− 0.43 (− 0.72, − 0.14)	0.004	< 0.001	74.8%	0.864
Europe/America	3	222	− 0.53 (− 1.70, 0.63)	0.367	< 0.001	92.3%
Analysis and subgroup results of Cinnamon supplementation on Postprandial blood glucose
Overall effect	8	463	− 2.28 (− 3.48, − 1.08)	< 0.001	< 0.001	94.4%
Analysis and subgroup results of Cinnamon supplementation on QUICKI
Overall effect	3	162	− 0.33 (− 0.72, 0.07)	0.103	0.268	24.0%
Analysis and subgroup results of Cinnamon supplementation on CRP
Overall effect	7	462	− 0.78 (− 1.28, − 0.27)	0.003	< 0.001	84.3%
Analysis and subgroup results of Cinnamon supplementation on IL-6
Overall effect	3	123	− 0.37 (− 0.90, 0.16)	0.168	0.119	53.1%
Analysis and subgroup results of Cinnamon supplementation on Fasting cholesterol
Overall effect	4	74	− 3.93 (− 6.23, − 1.64)	0.001	< 0.001	88.1%
Analysis and subgroup results of Cinnamon supplementation on Fasting LDL
Overall effect	4	74	− 2.52 (− 4.37, − 0.68)	0.007	< 0.001	88.0%
Analysis and subgroup results of Cinnamon supplementation on Fasting TG
Overall effect	4	74	− 2.67 (− 4.18, − 1.16)	0.001	0.001	81.0%
Analysis and subgroup results of Cinnamon supplementation on HDL
Overall effect	30	1780	0.56 (0.23, 0.89)	0.001	< 0.001	90.6%
Health Condition
Prediabetes/Diabetes	19	1198	0.65 (0.20, 1.09)	0.005	< 0.001	92.3%	0.507
Other conditions	11	582	0.42 (− 0.06, 0.91)	0.086	< 0.001	86.9%
Cinnamon dosage (mg/day)
2000 >	17	1014	0.29 (0.04, 0.54)	0.021	< 0.001	72.1%	0.075
2000 ≤	13	766	1.00 (0.26, 1.74)	0.008	< 0.001	95.2%
Intervention duration (weeks)
8 ≥	12	733	0.16 (− 0.16, 0.49)	0.319	< 0.001	78.0%	0.025
8 <	18	1047	0.87 (0.35, 1.39)	0.001	< 0.001	93.2%
Intervention Age (year)
50 ≥	12	700	1.12 (0.31, 1.93)	0.007	< 0.001	95.5%	0.042
50 <	18	1080	0.25 (0.02, 0.47)	0.031	< 0.001	68.4%
Baseline BMI
Healthy/Overweight (< 30 kg/m2)	19	1198	0.54 (0.10, 0.97)	0.016	< 0.001	92.0%	0.485
Obese (≥ 30 kg/m2)	8	469	0.75 (0.08, 1.42)	0.028	< 0.001	91.0%
Not given	3	113	0.31 (− 0.09, 0.70)	0.125	0.661	0.0%
Cinnamon type
C.cassia	5	216	0.34 (− 0.32, 1.01)	0.313	< 0.001	81.5%	0.004
C.verum	2	139	− 0.35 (− 0.82, 0.12)	0.140	0.166	47.8%
C.zeylanicum	3	116	0.02 (− 0.53, 0.58)	0.934	0.107	55.3%
Not given	20	1309	0.81 (0.37, 1.25)	< 0.001	< 0.001	92.6%
Continent
Asia	24	1536	0.62 (0.23, 1.01)	0.002	< 0.001	92.1%	0.420
Europe/America	6	244	0.35 (− 0.17, 0.88)	0.184	0.002	73.3%
Analysis and subgroup results of Cinnamon supplementation on LDL
Overall effect	28	1674	− 0.56 (− 0.86, − 0.25)	< 0.001	< 0.001	88.6%
Health Condition
Prediabetes/Diabetes	19	1191	− 0.50 (− 0.92, − 0.08)	0.019	< 0.001	91.3%	0.405
Other conditions	9	483	− 0.71 (−0.98, − 0.45)	< 0.001	0.056	47.3%
Cinnamon dosage (mg/day)
2000 >	16	975	−0.45 (− 0.76, − 0.13)	0.006	< 0.001	81.8%	0.460
2000 ≤	12	699	− 0.71 (− 1.32, − 0.10)	0.023	< 0.001	92.7%
Intervention duration (weeks)
8 ≥	11	666	− 0.29 (− 0.73, 0.15)	0.197	< 0.001	86.6%	0.152
8 <	17	1008	− 0.73 (− 1.14, − 0.32)	< 0.001	< 0.001	88.9%
Intervention Age (year)
50 ≥	10	601	− 1.04 (− 1.65, − 0.42)	0.001	< 0.001	91.1%	0.026
50 <	18	1073	− 0.27 (− 0.55, 0.01)	0.054	< 0.001	79.0%
Baseline BMI
Healthy/Overweight (< 30 kg/m2)	18	1152	− 0.71 (− 1.14, − 0.28)	0.001	< 0.001	91.6%	0.181
Obese (≥ 30 kg/m2)	7	409	− 0.35 (− 0.84, 0.13)	0.156	< 0.001	81.5%
Not given	3	113	− 0.16 (− 0.55, 0.23)	0.409	0.746	0.0%
Cinnamon type
C.cassia	5	216	− 0.19 (− 0.60, 0.21)	0.348	0.085	51.2%	0.053
C.verum	1	79	0.10 (− 0.34, 0.54)	0.658	–	–
C.zeylanicum	3	116	− 0.22 (− 0.78, 0.34)	0.438	0.103	55.9%
Not given	19	1263	− 0.73 (− 1.15, − 0.32)	0.001	< 0.001	91.3%
Continent
Asia	22	1430	− 0.70 (− 1.06, − 0.34)	< 0.001	< 0.001	90.2%	0.001
Europe/America	6	244	0.05 (− 0.20, 0.31)	0.683	0.513	0.0%
Analysis and subgroup results of Cinnamon supplementation on TC
Overall effect	29	1742	− 0.91 (− 1.31, − 0.52)	< 0.001	< 0.001	93.0%
Health Condition
Prediabetes/Diabetes	19	1199	− 1.08 (− 1.66, − 0.50)	< 0.001	< 0.001	95.0%	0.272
Other conditions	10	543	− 0.71 (− 1.02, − 0.40)	< 0.001	0.002	65.6%
Cinnamon dosage (mg/day)
2000 >	16	975	− 0.62 (− 1.02, − 0.21)	0.003	< 0.001	88.3%	0.136
2000 ≤	13	767	− 1.28 (− 2.06, − 0.50)	0.001	< 0.001	95.6%
Intervention duration (weeks)
8 ≥	12	734	− 0.54 (− 1.06, − 0.03)	0.038	< 0.001	90.7%	0.116
8 <	17	1008	− 1.17 (− 1.74, − 0.59)	< 0.001	< 0.001	94.0%
Intervention Age (year)
50 ≥	11	661	− 1.66 (− 2.51, − 0.80)	< 0.001	< 0.001	95.4%	0.011
50 <	18	1081	− 0.45 (− 0.81, − 0.08)	0.018	< 0.001	87.7%
Baseline BMI
Healthy/Overweight (< 30 kg/m2)	18	1160	− 1.24 (− 1.84, − 0.64)	< 0.001	< 0.001	95.2%	0.121
Obese (≥ 30 kg/m2)	8	469	− 0.44 (− 0.94, 0.06)	0.083	< 0.001	84.6%
Not given	3	113	− 0.64 (− 1.04, − 0.25)	0.001	0.953	0.0%
Cinnamon type
C.cassia	5	216	− 0.20 (− 0.79, 0.39)	0.506	0.002	76.4%	0.005
C.verum	2	139	− 0.11 (− 1.23, 1.00)	0.845	0.001	90.5%
C.zeylanicum	3	116	− 0.17 (− 0.54, 0.19)	0.350	0.860	0.0%
Not given	19	1271	− 1.34 (− 1.90, − 0.79)	< 0.001	< 0.001	94.9%
Continent
Asia	23	1498	− 1.15 (− 1.62, − 0.68)	< 0.001	< 0.001	94.1%	< 0.001
Europe/America	6	244	0.02 (− 0.37, 0.40)	0.937	0.060	52.8%
Analysis and subgroup results of Cinnamon supplementation on TG
Overall effect	30	1780	− 0.73 (− 1.08, − 0.39)	< 0.001	< 0.001	91.2%
Health Condition
Prediabetes/Diabetes	19	1198	− 0.97 (− 1.46, − 0.47)	< 0.001	< 0.001	93.5%	0.075
Other conditions	11	582	− 0.39 (− 0.78, 0.02)	0.061	< 0.001	81.6%
Cinnamon dosage (mg/day)
2000 >	17	1014	− 0.42 (− 0.75, − 0.10)	0.011	< 0.001	83.5%	0.060
2000 ≤	13	766	− 1.15 (− 1.84, − 0.46)	0.001	< 0.001	94.5%
Intervention duration (weeks)
8 ≥	12	733	− 0.48 (− 0.95, − 0.00)	0.050	< 0.001	89.3%	0.210
8 <	18	1047	− 0.91 (− 1.40, − 0.42)	< 0.001	< 0.001	92.2%
Intervention Age (year)
50 ≥	12	700	− 1.18 (− 1.95, − 0.42)	0.002	< 0.001	94.9%	0.076
50 <	18	1080	− 0.44 (− 0.74, − 0.14)	0.004	< 0.001	82.1%
Baseline BMI
Healthy/Overweight (< 30 kg/m2)	19	1198	− 0.82 (− 1.33, − 0.31)	0.002	< 0.001	93.9%	0.826
Obese (≥ 30 kg/m2)	8	469	− 0.64 (− 1.03, − 0.25)	0.001	< 0.001	74.5%
Not given	3	113	− 0.62 (− 1.14, − 0.11)	0.018	0.199	38.0%
Cinnamon type
C.cassia	5	216	− 0.23 (− 0.50, 0.04)	0.088	0.828	0.0%	0.007
C.verum	2	139	− 0.07 (− 0.40, 0.27)	0.694	0.389	0.0%
C.zeylanicum	3	116	− 0.03 (− 0.94, 0.89)	0.953	0.003	83.2%
Not given	20	1309	− 1.06 (− 1.54, − 0.58)	< 0.001	< 0.001	93.6%
Continent
Asia	24	1536	− 0.86 (− 1.27, − 0.44)	< 0.001	< 0.001	93.0%	0.029
Europe/America	6	244	− 0.31 (− 0.56, − 0.06)	0.016	0.987	0.0%
Analysis and subgroup results of Cinnamon supplementation on ALP
Overall effect	6	101	− 0.07 (− 0.47, 0.32)	0.720	0.488	0.0%
Analysis and subgroup results of Cinnamon supplementation on ALT
Overall effect	10	248	− 0.59 (− − 1.45, 0.28)	0.182	< 0.001	88.9%
Health Condition
Prediabetes/Diabetes	7	150	− 0.55 (− 0.98, − 0.12)	0.012	0.164	34.6%	0.922
Other conditions	3	98	− 0.71 (− 3.77, 2.37)	0.653	< 0.001	97.2%
Cinnamon dosage (mg/day)
2000 >	6	164	− 0.98 (− 2.00, 0.04)	0.060	< 0.001	87.5%	0.241
2000 ≤	4	84	0.02 (− 1.30, 1.34)	0.977	< 0.001	86.9%
Intervention duration (weeks)
8 ≥	2	50	0.81 (− 0.78, 2.40)	0.318	0.014	83.6%	0.057
8 <	8	198	− 0.93 (− 1.76, − 0.10)	0.027	< 0.001	84.7%
Intervention Age (year)
50 ≥	7	165	− 0.58 (− 1.86, 0.71)	0.377	< 0.001	92.2%	0.896
50 <	3	83	− 0.67 (− 1.24, − 0.11)	0.020	0.249	28.0%
Baseline BMI
Healthy/Overweight (< 30 kg/m2)	6	146	− 0.62 (− 2.15, 0.91)	0.425	< 0.001	93.5%	0.682
Obese (≥ 30 kg/m2)	1	22	− 0.29 (− 1.13, 0.56)	0.508	–	–
Not given	3	80	− 0.73 (− 1.24, − 0.21)	0.006	0.334	8.8%
Cinnamon type
C.cassia	2	31	− 0.02 (− 0.73, 0.69)	0.956	0.951	0.0%	0.275
C.verum	–	–	–	–	–	–
C.zeylanicum	–	–	–	–	–	–
Not given	8	217	− 0.73 (− 1.78, 0.33)	0.177	< 0.001	91.2%
Continent
Asia	8	209	− 0.70 (− 1.79, 0.39)	0.206	< 0.001	91.2%	0.398
Europe/America	2	39	− 0.16 (− 0.79, 0.47)	0.621	0.661	0.0%
Analysis and subgroup results of Cinnamon supplementation on AST
Overall effect	9	234	− 0.29 (− 0.96, 0.39)	0.406	< 0.001	82.4%
Analysis and subgroup results of Cinnamon supplementation on BUN
Overall effect	5	169	− 0.50 (− 1.74, 0.74)	0.428	< 0.001	90.0%
Analysis and subgroup results of Cinnamon supplementation on MDA
Overall effect	5	289	− 0.76 (− 1.07, − 0.45)	< 0.001	0.193	34.3%
Analysis and subgroup results of Cinnamon supplementation on TAC
Overall effect	4	268	0.52 (− 0.05, 1.08)	0.073	0.002	79.1%

Footprint: ALP, Alkaline Phosphatase; ALT, Alanine Aminotransferase; AST, Aspartate Aminotransferase; BF, Body fat; BMI, Body Mass Index; BUN, Blood Urea Nitrogen; CI, Confidence Interval; CRP, C-Reactive Protein; DBP, Diastolic Blood Pressure; FBS, Fasting Blood Sugar; HbA1c, Hemoglobin A1C; HDL, High-Density Lipoprotein; HOMA-IR, Homeostatic Model Assessment of Insulin Resistance; IL-6, Interleukin-6; INT, Intervention Group; LDL, Low-Density Lipoprotein; MDA, Malondialdehyde; QUICKI, Quantitative Insulin Sensitivity Check Index; SBP, Systolic Blood Pressure; SMD, Standardised Mean Difference; TAC, Total Antioxidant Capacity; TC, Total Cholesterol; TG, Triglycerides; WC, Waist Circumference; WHR, Waist-to-Hip Ratio

Bold formatting has been used to denote statistically significant findings (p < 0.05)

Cinnamon supplementation showed a greater impact on fasting glucose, HbA1c, HDL-C, TG, and ALT in T2DM or prediabetic participants, while WC and SBP were more significantly affected in other health conditions. DBP, HOMA-IR, LDL-C, and TC improved significantly across both health conditions. No substantial effects were observed on BMI, weight, and fasting insulin in these subgroups.

For dosages > 2000 mg/day, significant effects were observed in SBP and fasting insulin. In contrast, doses ≤ 2000 mg/day had a more notable effect on WC, DBP, and HbA1c. Both dosage groups showed significant effects on fasting glucose, HOMA-IR, HDL-C, LDL-C, TC, and TG, while BMI, weight, and ALT were unaffected.

Regarding intervention duration, studies lasting < 8 weeks showed significant effects on weight, SBP, HbA1c, HDL-C, TG, and ALT. Both duration groups saw improvements in DBP, fasting glucose, HOMA-IR, LDL, TC, and TG, while BMI, WC and fasting insulin remained unaffected in both categories.

Participants aged ≤ 50 showed significant improvements in WC, and SBP, while those over 50 exhibited significant reductions in ALT. Both age groups demonstrated significant effects on DBP, fasting glucose, HbA1c, HOMA-IR, HDL-C, LDL-C, TC, and TG. No significant changes in BMI, weight, and fasting insulin were observed in either age group.

For baseline BMI, cinnamon supplementation significantly impacted HOMA-IR, LDL-C, and TC in healthy or overweight individuals, while significant improvements in WC and SBP were observed in obese participants. Both BMI groups showed effects on DBP, fasting glucose, HbA1c, HDL-C, and TG. No significant effects were seen for BMI, weight, fasting insulin, and ALT in either category.

Regarding cinnamon types, C. cassia significantly reduced fasting glucose, LDL-C, TC, and TG. C. verum lowered DBP, and both C. cassia and C. verum affected SBP, while C. zeylanicum impacted HOMA-IR. No significant effects were found for BMI, WC, weight, fasting insulin, HbA1c, HDL-C, and ALT across these cinnamon types.

Regionally, cinnamon supplementation yielded significant effects on WC, fasting glucose, fasting insulin, HbA1c, HOMA-IR, HDL-C, LDL-C, and TC in studies conducted in Asia. SBP was more significantly affected in studies from Europe or America, with DBP and TG showing significant improvements across both regions. BMI, weight, and ALT levels remained unaffected across regions.

Meta-regression and non-linear dose–response analysis

Meta-regression analysis showed a linear relationship between dosage and significant change in fasting insulin level (P = 0.02). Additionally, a non-linear dose–response regression model was employed to explore the relationship between cinnamon supplementation and cardiovascular outcomes. A significant dose-dependent reduction was observed for BMI (P = 0.026), fasting insulin (P < 0.001), LDL (P = 0.005) TC (P = 0.011), and TG (P = 0.016), with approximate optimal doses of 600, 1000, 6000, 6000, and 6000 mg/day, respectively. Also, a significant association was noted between cinnamon dose and HDL-C increase (P < 0.001), with an optimal dose for HDL-C enhancement at around 6000 mg/day. (Supplementary Figs. 8,9,10 and 11).

GRADE assessment

The GRADE profile for cinnamon supplementation outcomes is summarized in Table 4, with the quality of evidence rated as very low across all outcomes.

Table 4.

GRADE profile of cinnamon supplementation on cardiovascular risk factors

Outcomes	Risk of bias	Inconsistency	Indirectness	Imprecision	Publication Bias	Number (INT/CON)	SMD (95%CI)	Quality of evidence
BF	Seriousa	Very seriousb	Not serious	Very seriousc, d	None	183/177	− 0.19 (− 0.88, 0.50)	⨁◯◯◯ Very low
BMI	Seriousa	Very seriousb	Not serious	Seriousc	None	743/762	− 0.13 (− 0.40, 0.13)	⨁◯◯◯ Very low
WC	Seriousa	Very seriousb	Not serious	Not serious	None	385/382	− 0.40 (− 0.73, − 0.06)	⨁◯◯◯ Very low
Weight	Seriousa	Very seriousb	Not serious	Seriousc	None	521/517	− 0.08 (− 0.41, 0.25)	⨁◯◯◯ Very low
WHR	Seriousa	Not serious	Not serious	Very seriousc, d	Publication bias strongly Suspectede	124/124	− 0.28 (− 0.61, 0.06)	⨁◯◯◯ Very low
DBP	Seriousa	Very seriousb	Not serious	Not serious	None	350/353	− 1.04 (− 1.54, − 0.55)	⨁◯◯◯ Very low
SBP	Seriousa	Very seriousb	Not serious	Not serious	None	362/363	− 0.85 (− 1.54, − 0.16)	⨁◯◯◯ Very low
Fasting glucose	Seriousa	Very seriousb	Not serious	Not serious	Publication bias strongly Suspectede	1029/969	− 1.45 (− 1.88, − 1.02)	⨁◯◯◯ Very low
Fasting insulin	Very seriousa	Not serious	Not serious	Very seriousc, d	Publication bias strongly Suspectede	172/177	0.09 (− 0.22, 0.39)	⨁◯◯◯ Very low
Glucose	Seriousa	Very seriousb	Not serious	Very seriousc, d	None	181/190	− 0.39 (− 1.17, 0.40)	⨁◯◯◯ Very low
HbA1c	Seriousa	Very seriousb	Not serious	Not serious	None	972/904	− 0.71 (− 1.02, − 0.40)	⨁◯◯◯ Very low
HOMA-R	Seriousa	Very seriousb	Not serious	Not serious	None	591/620	− 0.54 (− 0.82, − 0.26)	⨁◯◯◯ Very low
Insulin	Seriousa	Very seriousb	Not serious	Not serious	None	503/528	− 0.45 (− 0.74, − 0.15)	⨁◯◯◯ Very low
Postprandial blood glucose	Seriousa	Very seriousb	Seriousf	Not serious	Publication bias strongly Suspectede	221/242	− 2.28 (− 3.48, − 1.08)	⨁◯◯◯ Very low
QUICKI	Seriousa	Not serious	Seriousf	Very seriousc, d	None	79/83	− 0.33 (− 0.72, 0.07)	⨁◯◯◯ Very low
CRP	Seriousa	Very seriousb	Seriousf	Not serious	None	229/233	− 0.78 (− 1.28, − 0.27)	⨁◯◯◯ Very low
IL-6	Very seriousa	Seriousb	Very seriousf	Very seriousc, d	None	62/61	− 0.37 (− 0.90, 0.16)	⨁◯◯◯ Very low
Fasting cholesterol	Very seriousa	Very seriousb	Very seriousf	Seriousd	Publication bias strongly Suspectede	37/37	− 3.93 (− 6.23, − 1.64)	⨁◯◯◯ Very low
Fasting LDL	Very seriousa	Very seriousb	Very seriousf	Seriousd	Publication bias strongly Suspectede	37/37	− 2.52 (− 4.37, − 0.68)	⨁◯◯◯ Very low
Fasting TG	Very seriousa	Very seriousb	Very seriousf	Seriousd	None	37/37	− 2.67 (− 4.18, − 1.16)	⨁◯◯◯ Very low
HDL	Seriousa	Very seriousb	Not serious	Not serious	None	921/859	0.56 (0.23, 0.89)	⨁◯◯◯ Very low
LDL	Seriousa	Very seriousb	Not serious	Not serious	None	866/808	− 0.56 (− 0.86, − 0.25)	⨁◯◯◯ Very low
TC	Seriousa	Very seriousb	Not serious	Not serious	None	903/839	− 0.91 (− 1.31, − 0.52)	⨁◯◯◯ Very low
TG	Seriousa	Very seriousb	Not serious	Not serious	Publication bias strongly Suspectede	922/858	− 0.73 (− 1.08, − 0.39)	⨁◯◯◯ Very low
ALP	Very seriousa	Not serious	Not serious	Very seriousc, d	Publication bias strongly Suspectede	51/50	− 0.07 (− 0.47, 0.32)	⨁◯◯◯ Very low
ALT	Very seriousa	Very seriousb	Not serious	Very seriousc, d	None	138/110	− 0.59 (− 1.45, 0.28)	⨁◯◯◯ Very low
AST	Very seriousa	Very seriousb	Not serious	Very seriousc, d	None	131/103	− 0.29 (− 0.96, 0.39)	⨁◯◯◯ Very low
BUN	Very seriousa	Very seriousb	Seriousf	Very seriousc, d	None	84/85	− 0.50 (− 1.74, 0.74)	⨁◯◯◯ Very low
MDA	Seriousa	Not serious	Seriousf	Seriousd	None	142/147	− 0.76 (− 1.07, − 0.45)	⨁◯◯◯ Very low
TAC	Seriousa	Very seriousb	Seriousf	Very seriousc, d	Publication bias strongly Suspectede	131/137	0.52 (− 0.05, 1.08)	⨁◯◯◯ Very low

Footprint: ALP, Alkaline Phosphatase; ALT, Alanine Aminotransferase; AST, Aspartate Aminotransferase; BF, Body fat; BMI, Body Mass Index; BUN, Blood Urea Nitrogen; CI, Confidence Interval; CRP, C-Reactive Protein; DBP, Diastolic Blood Pressure; FBS, Fasting Blood Sugar; HbA1c, Hemoglobin A1C; HDL, High-Density Lipoprotein; HOMA-IR, Homeostatic Model Assessment of Insulin Resistance; IL-6, Interleukin-6; INT, Intervention Group; LDL, Low-Density Lipoprotein; MDA, Malondialdehyde; QUICKI, Quantitative Insulin Sensitivity Check Index; SBP, Systolic Blood Pressure; SMD, Standardised Mean Difference; TAC, Total Antioxidant Capacity; TC, Total Cholesterol; TG, Triglycerides; WC, Waist Circumference; WHR, Waist-to-Hip Ratio

Explanations

a. Downgraded since more than 50% of the participants were from high-risk bias studies

b. The I² value was > 50% (or Heterogeneity among the studies was high)

c. Downgraded since the 95% CI crosses the threshold of interest

d. Downgraded since the participants included were less than 400 people

e. Publication Bias was detected through Egger and Begg's test. (p-value < 0.05)

f. Downgraded for indirectness in the country

Discussion

To our knowledge, this is the first GRADE-assessed systematic review and dose–response meta-analysis to evaluate the effects of cinnamon supplementation on metabolic and cardiovascular factors. Our review included 49 RCTs with a total of 3,038 participants, revealing that cinnamon improved WC, blood pressure, glycemic indices, CRP, lipid profile, and MDA in adults. Notably, cinnamon supplementation selectively reduced WC without significantly affecting overall body weight, BMI, or body fat, potentially due to its capacity to enhance insulin sensitivity, reduce visceral fat, and exert anti-inflammatory effects that may specifically target abdominal fat [24, 73]. Further studies are needed to confirm these findings and elucidate the underlying mechanisms. The reduction in CRP without corresponding changes in IL-6 may reflect cinnamon's influence on systemic inflammation without impacting IL-6 pathways. Furthermore, our findings on liver enzymes indicate that cinnamon should not be regarded as a liver function enhancer. The observed decrease in MDA without an increase in TAC suggests a reduction in lipid peroxidation rather than an overall boost in antioxidant capacity. Our results must be interpreted with precaution due to the high heterogeneity in most of the studied factors.

Subgroup analysis revealed that certain factors, including higher doses (≥ 2000 mg/day) and longer durations (> 8 weeks), were associated with larger effect sizes. Non-linear regression indicated a significant dose–response relationship for fasting insulin, LDL-C, TC, TG, and HDL-C, with the optimal dose for most beneficial effects, aside from insulin, identified as 6000 mg/day. The acceptable daily intake of coumarin in Europe is set at 0.1 mg/kg/day to ensure safe consumption [74]. Differences in cinnamon's effects can be attributed to compositional variations; Cassia contains high coumarin levels (1 mg/g), a compound with potential toxicity, while Ceylon (C. verum/zeylanicum) has minimal coumarin (< 0.01 mg/g), making it safer for regular or high-dose use [75]. Additionally, Cassia has a higher essential oil content, especially cinnamaldehyde, whereas Ceylon offers a broader range of antioxidant polyphenols [75–77].

Younger adults (≤ 50 years) experienced greater benefits from cinnamon supplementation than older adults (> 50 years). This aligns with a large observational study finding lifestyle interventions had a more substantial impact on cardiometabolic markers in younger adults [78]. Younger individuals typically have greater physical and cognitive abilities to benefit from lifestyle modifications, while older adults may face more health complications and have a reduced capacity for adaptation due to age-related decline in bodily functions and cognitive processing.

Beneficial effects of cinnamon on metabolic and cardiovascular health can be related to the multiple molecular mechanisms attributed to its bioactive compounds, primarily cinnamaldehyde, cinnamic acid, and polyphenols. One key mechanism is enhancement of insulin sensitivity and regulation of glucose metabolism by cinnamon. Cinnamaldehyde can activate insulin receptors and promote glucose transporter 4 (GLUT4) translocation in muscle and fat tissues, facilitating greater glucose uptake [79]. Moreover, cinnamon activates the phosphorylation process in insulin signaling cascade, leading to the activation of intracellular cascade events [80]. This activity lowers blood glucose levels and improves insulin resistance, potentially reducing visceral fat, which is associated with insulin resistance and abdominal obesity. Cinnamic acid also supports glucose regulation by improving glucose uptake [81].

Regarding lipid metabolism, bioactive compounds of cinnamon inhibit hepatic Hydroxymethylglutaryl-CoA (HMG-CoA) reductase, a key enzyme in cholesterol biosynthesis, resulting in decreased LDL-C and increased HDL-C levels [82]. Cinnamaldehyde and cinnamic acid have also been shown to enhance lipid oxidation and reduce triglyceride levels [83]. Moreover, cinnamon reduces cholesterol and fatty acid absorption in gut cells by inhibiting Niemann-Pick C1-like 1 and Cd36 mRNA receptors [80]. Furthermore, cinnamon upregulates the expression of genes that suppress triglyceride accumulation, cholesterol levels, and apolipoprotein-B48 synthesis at the mRNA level [84].

The anti-inflammatory properties of cinnamon contribute further to its metabolic benefits. Cinnamaldehyde and cinnamic acid can inhibit the nuclear factor-kappa B (NF-Κb) pathway, a master regulator of inflammation, leading to reduced production of pro-inflammatory cytokines [85, 86]. Our study showed a significant reduction in CRP, which supports the ability of cinnamon in reducing systemic inflammation. The fact that IL-6 was unaffected by cinnamon may indicate selective anti-inflammatory actions, possibly targeting specific pathways influenced by active components of cinnamon rather than broad cytokine suppression. Therefore, additional studies focusing on other inflammatory pathways are needed to determine the molecular mechanisms of anti-inflammatory actions of cinnamon. Antioxidant effects are another important aspect of cinnamon, particularly due to its high polyphenol content, including proanthocyanidins [87]. These antioxidants directly scavenge reactive oxygen species (ROS), reducing oxidative stress markers like MDA [88].

Several molecular mechanisms have been identified to explain the hypotensive effects of cinnamon. HTN is often associated with increased oxidative stress and elevated inflammatory markers, and cinnamon, as a potent antioxidant, helps to reduce ROS, thus mitigating oxidative stress [89]. Furthermore, the antioxidant properties of cinnamon contribute to a decrease in the production of nitric oxide (NO), which serves both as a powerful vasodilator and a marker of oxidative stress [90]. However, cinnamon may exert its anti-hypertensive effects through other pathways. Transient receptor potential ankyrin 1 (TRPA1) channels in arteries, when activated by cinnamon, stimulate the release of calcitonin gene-related peptide, resulting in vasodilation. Therefore, cinnamon has been shown to exert a hypotensive effect by inhibiting calcium release from intracellular stores, leading to vascular smooth muscle relaxation and reduced blood pressure [91, 92].

The RoB 2 assessment for the 49 RCTs included in the meta-analysis reveals significant methodological limitations, with 43 studies rated as poor quality, primarily due to high risk of bias in allocation concealment (44 studies) and blinding of outcome assessment (38 studies). These weaknesses, compounded by variable issues in random sequence generation (11 unclear, 1 high risk) and blinding of participants/personnel (18 highs, 5 unclear), suggest potential selection, performance, and detection biases that undermine the reliability of the findings. Despite these concerns, all studies demonstrated low risk in selective outcome reporting and other sources of bias, indicating transparent reporting and absence of additional methodological flaws. Only one study was rated as good quality, with five rated as fair, highlighting the rarity of robust methodology.

Given the very low certainty of evidence and the high risk of bias in the included studies, the potential beneficial effects of cinnamon on the assessed outcomes should be interpreted with caution and considered as possible rather than definitive.

The predominance of poor-quality studies, reflected in the very low GRADE ratings, necessitates cautious interpretation of cinnamon’s effects on cardiovascular risk factors and underscores the urgent need for high-quality RCTs with improved randomization, concealment, and blinding to provide more definitive evidence.

Clinical implications of findings

The results of this meta-analysis offer meaningful clinical insights for healthcare professionals managing patients at risk of cardiovascular and metabolic diseases. The significant reductions observed in fasting plasma glucose, HbA1c, HOMA-IR, fasting insulin, and postprandial blood glucose levels suggest that cinnamon supplementation can serve as an effective adjunctive therapy for improving glycemic control in adults with T2DM, prediabetes, metabolic syndrome, and related disorders. These glycemic benefits were consistently observed across a range of doses and intervention durations, highlighting cinnamon’s potential as a complementary strategy alongside conventional glucose-lowering therapies.

Furthermore, the significant improvements in both SBP and DBP indicate that cinnamon supplementation may offer additional cardiovascular protection, particularly for individuals with coexisting hypertension or elevated blood pressure—a common comorbidity in patients with metabolic dysfunction. A small reduction in blood pressure may seem clinically insignificant to an individual patient, but it can have significant effects on population health. Large meta-analyses show that the risk of cardiovascular disease is consistently reduced with decreasing blood pressure. Etihad et al. report that a 10 mmHg reduction in SBP reduces major cardiovascular events by approximately 20% [93, 94]. While no significant effects were observed on body weight, BMI, or body fat, the modest but significant reduction in WC underscores cinnamon’s possible role in targeting central adiposity, which is strongly linked to cardiometabolic risk. The modest decreases in WC, lipid profile, and glycemic indices associated with cinnamon supplementation indicate that it may serve as a supportive option for cardiovascular risk factor management [95, 96]. While modest, it may carry clinical implications depending on the population studied and the context of the intervention. Nonetheless, the clinical relevance of these findings should be viewed with caution. Although the reductions in outcomes are statistically significant, they may fall short of the minimal clinically important difference (MCID) for certain populations.

Clinicians should consider cinnamon supplementation, particularly in populations with impaired glucose metabolism and elevated blood pressure, as part of an integrative care approach. Although the supplementation appears generally safe and well-tolerated across diverse adult populations, practitioners should be mindful of the variability in individual responses, as well as the high heterogeneity in the included trials. Personalizing the dose and duration of cinnamon intake based on patient characteristics, therapeutic goals, and tolerability is advisable to maximize potential benefits.

Despite the observed clinical benefits, it is essential to acknowledge that data on the potential adverse effects and long-term safety of cinnamon supplementation remain limited. While most trials included in this meta-analysis reported no serious adverse events and described cinnamon as generally well-tolerated, systematic reporting of safety outcomes was inconsistent and often lacking in detail. Concerns about coumarin content—particularly in Cassia cinnamon—warrant consideration, as high doses over extended periods may pose risks of hepatotoxicity and other toxicological effects [97]. Moreover, potential interactions with antidiabetic and antihypertensive medications, as well as variability in cinnamon species, formulations, and purity, should be carefully evaluated in clinical practice. Future trials with rigorous safety assessments and longer intervention durations are needed to more definitively establish the long-term safety profile of cinnamon supplementation. Until such data are available, clinicians should exercise caution, prioritize standardized extracts with low coumarin content, and monitor patients regularly when recommending cinnamon as an adjunctive therapy.

Strengths and limitations

This meta-analysis represents a robust and comprehensive evaluation of cinnamon supplementation’s effects on cardiovascular risk factors, underpinned by a meticulous methodological framework. By adhering to the PRISMA guidelines and registering the protocol with PROSPERO, we ensured transparency, reproducibility, and alignment with the highest standards of systematic review conduct. The extensive literature search, spanning multiple databases (Cochrane, Web of Science, Medline, Scopus, Embase) and supplemented by manual reference screening, minimized the risk of overlooking relevant studies, capturing 49 RCTs with 3,038 participants. The application of the GRADE framework to assess evidence quality provided a rigorous evaluation of the certainty of findings, enhancing their reliability for clinical and research applications. Advanced statistical approaches, including meta-regression, non-linear dose–response analyses, and subgroup analyses, allowed us to elucidate dose-dependent effects and identify optimal dosages, offering nuanced insights into cinnamon’s therapeutic potential across diverse populations, health conditions, and cinnamon types (C. cassia, C. verum, C. zeylanicum). This comprehensive scope, coupled with the inclusion of a wide range of outcomes (anthropometric, glycemic, lipid, inflammatory, and oxidative stress markers), positions our study as a significant advancement over prior meta-analyses that focused on narrower endpoints, such as glycemic control or lipid profiles alone.

Our study offers distinct advantages over previous meta-analyses in this field. Unlike earlier reviews that often concentrated on specific outcomes, such as glycemic control in T2DM or lipid modulation, our analysis encompasses a broad spectrum of cardiovascular risk factors, including blood pressure, waist circumference, and inflammatory biomarkers like CRP. This holistic approach provides a more complete understanding of cinnamon’s multifaceted benefits, particularly for populations with T2DM, prediabetes, PCOS, and metabolic syndrome. The inclusion of 49 RCTs, compared to smaller datasets in prior studies, enhances the statistical power and generalizability of our findings. Additionally, our subgroup analyses based on age, baseline BMI, cinnamon type, and geographic region reveal critical patterns in treatment response, offering practical guidance for personalized interventions. The use of non-linear dose–response modeling further distinguishes our work by identifying optimal dosing strategies, a feature absent in many prior analyses. By addressing these gaps, our study contributes essential evidence to support the integration of cinnamon supplementation into evidence-based clinical practice and public health strategies.

Despite these strengths, several limitations must be acknowledged to contextualize our findings. The high heterogeneity observed across outcomes (I² > 80% for most parameters) reflects variability in study designs, participant characteristics, cinnamon formulations, and intervention durations, which may influence the precision of our effect estimates. Although we employed a random-effects model and conducted subgroup and sensitivity analyses to mitigate this, residual confounding cannot be entirely ruled out. The exclusion of non-English studies introduces potential language bias, possibly limiting the applicability of our findings in diverse cultural and geographic contexts. Publication bias, detected for some outcomes, suggests that negative or null results may be underrepresented, potentially overestimating cinnamon’s effects. The reliance on SMDs rather than weighted mean differences (WMDs) for outcomes with heterogeneous units (e.g., insulin, inflammatory markers) was necessary but may reduce clinical interpretability. Furthermore, the lack of standardization in cinnamon preparations (e.g., differences in coumarin content between C. cassia and C. verum) and the absence of detailed reporting on cinnamon extraction methods or plant parts used in many studies introduce uncertainty into dose–response interpretations. The short duration of most included trials (4–24 weeks) limits insights into the long-term safety and efficacy of cinnamon supplementation, particularly at higher doses. Finally, the very low GRADE ratings for our outcomes, underscore the need for future high-quality, large-scale RCTs to confirm our findings and address these methodological shortcomings.

Future research directions

Future research should focus on addressing the identified gaps in the current evidence base for cinnamon supplementation to enhance its clinical applicability and safety profile. Given the significant heterogeneity observed across outcomes (I² > 80% for most parameters), large-scale, high-quality RCTs with standardized cinnamon formulations and clearly defined coumarin content are essential to reduce variability and improve the precision of effect estimates. Long-term studies extending beyond 24 weeks are needed to evaluate the sustained efficacy and safety of cinnamon, particularly at higher doses (e.g., 6000 mg/day, optimal for lipid profiles), and to assess potential risks such as hepatotoxicity associated with coumarin in C. cassia. Investigating optimal dosing strategies tailored to specific populations and considering factors like age (≤ 50 vs. > 50 years), baseline BMI, and geographic region could refine therapeutic recommendations. Additionally, studies should explore potential drug interactions between cinnamon and common medications for diabetes, hypertension, and dyslipidemia to ensure safe integration into clinical practice.

The molecular mechanisms underlying cinnamon’s beneficial effects on glycemic control, lipid profiles, blood pressure, and inflammation warrant further exploration. Advanced omics approaches (e.g., transcriptomics, metabolomics) could elucidate the roles of bioactive compounds like cinnamaldehyde, cinnamic acid, and polyphenols in modulating insulin signaling, lipid metabolism, and inflammatory pathways, such as NF-κB. The selective reduction in CRP without affecting IL-6 suggests specific anti-inflammatory pathways that require further investigation to understand cinnamon’s targeted effects. Research into cinnamon’s impact on gut microbiota and its potential role in mediating metabolic benefits could provide novel insights into its mechanism of action, particularly for visceral fat reduction (e.g., waist circumference). Studies comparing different cinnamon forms (e.g., whole powder, extracts, or isolated compounds) and delivery methods (e.g., capsules, functional foods) could optimize bioavailability and therapeutic outcomes, addressing the current lack of standardization in intervention protocols.

Further investigation is needed to explore cinnamon’s effects in understudied subpopulations, such as individuals with gestational diabetes, rheumatoid arthritis, or NAFLD, where preliminary evidence suggests potential benefits. The observed regional differences (e.g., stronger effects on glycemic and lipid outcomes in Asian studies) highlight the need for global, multi-center trials to assess the influence of genetic polymorphisms, dietary patterns, and environmental factors on treatment response. Research into synergistic effects of cinnamon with other natural compounds (e.g., turmeric, ginger) or conventional therapies could enhance its cardiometabolic benefits, potentially leading to combination therapies. Additionally, studies examining cinnamon’s broader health impacts, such as its antioxidant properties (evidenced by reduced malondialdehyde) or potential neuroprotective and anticancer effects, could expand its therapeutic applications. Cost-effectiveness analyses comparing cinnamon supplementation with standard treatments would provide critical data for policymakers and healthcare providers, supporting its integration into public health strategies. Finally, developing cinnamon-based nutraceuticals or functional foods through interdisciplinary research could facilitate practical dietary interventions, ensuring accessibility and scalability for diverse populations.

Conclusions

This systematic review and meta-analysis provides robust evidence supporting the effectiveness of cinnamon supplementation in ameliorating various risk factors for cardiovascular diseases. The significant reductions observed in WC, blood pressure, fasting glucose, and lipid profiles, along with improvements in inflammatory markers and oxidative stress parameters, underscore cinnamon's potential as a complementary approach to conventional therapies. Given its favorable safety profile and accessibility, healthcare practitioners may consider incorporating cinnamon supplementation into dietary recommendations for individuals at risk of cardiovascular diseases. Future research should focus on elucidating the mechanisms underlying these effects and evaluating long-term outcomes to establish optimal dosages and formulations for clinical practice.

Abbreviations

ALP

Alkaline phosphatase

ALT

Alanine aminotransferase

AMP

Adenosine monophosphate

AST

Aspartate aminotransferase

BF

Body fat

BMI

Body mass index

BUN

Blood urea nitrogen

CENTRAL

Central register of controlled trials

CI

Confidence interval

CIN

Cinnamaldehyde

CRP

C-reactive protein

CVD

Cardiovascular diseases

CVH

Cardiovascular health

DBP

Diastolic blood pressure

eNOS

Endothelial NO synthase

FBG

Fasting blood glucose

FPG

Fasting plasma glucose

GLUT-4

Glucose transporter-4

HbA1c

Hemoglobin A1c

HDL-C

High-density lipoprotein cholesterol

HOMA-IR

Homeostatic model assessment of insulin resistance

HTN

Hypertension

IGF-1

Insulin-like growth factor-1

IGT

Impaired glucose tolerance

IL-6

Interleukin-6

IR

Insulin resistance

IRS-1

Insulin receptor substrate 1

LDL-C

Low-density lipoprotein cholesterol

LE8

Life’s essential 8

MDA

Malondialdehyde

MetS

Metabolic syndrome

MS

Multiple sclerosis

NAFLD

Non-alcoholic fatty liver disease

NO

Nitric oxide

PCOS

Polycystic ovary syndrome

PI3-K

Phosphatidylinositol 3-kinase

PRISMA

Preferred reporting items for systematic reviews and meta-analyses

PROSPERO

Prospective register of systematic reviews

QUICKI

Quantitative insulin sensitivity check index

RA

Rheumatoid arthritis

RCT

Randomized controlled trial

SBP

Systolic blood pressure

SMD

Standardized mean difference

T2DM

Type 2 diabetes mellitus

TAC

Total antioxidant capacity

TC

Total cholesterol

TG

Triglycerides

WC

Waist circumference

WHR

Waist-to-hip ratio

Author contributions

Designing this study: Ali Jafari. Performed this study: Ali Jafari, Helia Mardani, Amir Hossein Faghfouri Drafted the article: Alireza Alaghi, Vali Musazadeh, Minoo AhmadianMoghaddam Revised the article critically for important intellectual content: Vali Musazadeh, Ali Jafari Approved the version to be published: Ali Jafari, Helia Mardani, Amir Hossein Faghfouri, Minoo AhmadianMoghaddam, Alireza Alaghi, Vali Musazadeh.

Funding

None.

Availability of data and materials

The original data used during the current study can be obtained by contacting the corresponding author.

Declarations

Ethics approval and consent to participate

Not applicable.

Consent for publication

Not applicable.

Competing interests

The authors declare that they have no conflict of interest.