A 2013 systematic review of 10 randomized controlled trials (RCTs) with a total of 543 patients with type 2 diabetes evaluated the effect of cinnamon (120 mg/d to 6 g/d) on measures of glycemic control.1 Study duration ranged from 4 to 18 weeks. Fasting glucose levels demonstrated small but statistically significant reductions (−24.6 mg/dL; 95% confidence interval [CI], −40.5 to −8.7 mg/dL), whereas hemoglobin A1C levels didn’t differ between treatment and control groups (−0.16%; 95% CI, −0.39% to 0.02%). Study limitations included heterogeneity of cinnamon dosing and formulation and concurrent use of oral hypoglycemic agents.
Studies of glycemic control produce mixed results
A 2012 systematic review of 10 RCTs comprising 577 patients with type 1 (72 patients) or type 2 (505 patients) diabetes evaluated the effects of cinnamon supplements (mean dose, 1.9 g/d) on glycemic control compared with placebo, active control, or no treatment.2 Study duration ranged from 4.3 to 16 weeks (mean, 10.8 weeks). Studies evaluating hemoglobin A1C lasted at least 12 weeks.
Fasting glucose as measured in 8 studies (338 patients) and hemoglobin A1C as measured in 6 studies (405 patients) didn’t differ between treatment groups (mean fasting glucose difference = −0.91 mmol/L; 95% CI, −1.93 to 0.11; mean hemoglobin A1C difference = −0.06; 95% CI, −0.29 to 0.18). The risk for bias was assessed as high or unclear in 8 studies and moderate in 2 studies.
A 2012 systematic review and meta-analysis of 6 RCTs including 435 patients with type 2 diabetes evaluated the impact of cinnamon supplements (1 to 6 g/d) on glycemic control.3 Participants consumed cinnamon for 40 to 160 days. Hemoglobin A1C decreased by 0.09% (95% CI, 0.04% to 0.14%) in 5 trials (375 patients), and fasting glucose decreased by 0.84 mmol/L (CI, 0.66 to 1.02) in 5 trials (326 patients). Study limitations included heterogeneity of cinnamon dosing and study population.
The American Diabetes Association finds insufficient evidence to support the use of herbs or spices, including cinnamon, in treating diabetes.4
Meta-analyses of multiple small, lower-quality studies yield uncertain conclusions. If cinnamon does improve glycemic control, the benefit is minimal—but so is therisk.