Cinnamon Supplementation in Patients with Type 2 Diabetes Mellitus

Antony Q. Pham, B.S.; Helen Kourlas, Pharm.D.; David Q. Pham, Pharm.D.


Pharmacotherapy. 2007;27(4):595-599. 

In This Article

Clinical Trials

Three clinical trials evaluating cinnamon supplementation in patients with type 2 diabetes were identified: two were prospective, randomized, double-blind, placebo-controlled, peer-reviewed trials, and one was a prospective, placebo-controlled, peer-reviewed trial. The first prospective, randomized, double-blind, placebo-controlled clinical trial was published in 2003.[4] The study objective was to investigate the effects of Cinnamomum cassia powder on fasting blood glucose, triglyceride, and total cholesterol levels in patients with type 2 diabetes. Sixty Pakistani patients (30 men, 30 women) with type 2 diabetes were randomly divided into six groups. Group 1 received cinnamon 1 g/day (one 500-mg capsule after lunch and dinner); group 2 received cinnamon 3 g/day (two 500-mg capsules after breakfast, lunch, and dinner); and group 3 received cinnamon 6 g/day (four 500-mg capsules after breakfast, lunch, and dinner). Patients in groups 4-6 received identical placebo capsules corresponding to the number of capsules given to groups 1-3, respectively.

The intervention lasted 40 days and was followed by a 20-day washout period. Mean baseline fasting glucose levels ranged from 205.2-300.6 mg/dl. Although not reported in the study, these levels correspond to A1C values of 8.0-10.5%.[1] All patients continued receiving their sulfonylurea drug therapy and were instructed to maintain their normal diet throughout the study. Patients receiving insulin were excluded from the study. Compliance was monitored by capsule count. Blood samples were collected on study days 0 (baseline), 20, 40, and 60.

At day 40, significant reductions in serum glucose levels were noted in patients receiving cinnamon 1, 3, and 6 g/day compared with those receiving placebo (p<0.05); only the group receiving 6 g/day showed significant reductions in serum glucose levels at day 20 (p<0.05). All patients in the three treatment groups experienced elevated glucose levels after the 20-day washout period. Only the group receiving cinnamon 1 g/day still showed significant reductions compared with those receiving placebo after the washout period. Overall reductions in fasting glucose levels ranged from 18-29% ( Table 1 ). No adverse effects were reported. The researchers concluded that dietary cinnamon can safely and effectively lower fasting glucose concentrations in patients with type 2 diabetes.

Although the study results indicated a significant effect of cinnamon on blood glucose level, several factors must be considered before a clear conclusion can be drawn. First, the study was conducted in Pakistani patients with poorly controlled diabetes whose baseline glucose levels were higher than those of other patients in subsequent cinnamon trials. Patients with diabetes usually have better glucose control. In fact, a 2004 report indicated A1C values below 8% in 62.8% of western patients with diabetes.[12] The study involving the Pakistani patients with poorly controlled diabetes may actually have amplified the positive effects of cinnamon. Further, the trial was limited by a small sample size (60 patients). In addition, nutritional differences were not standardized during the trial. Dietary standardization of all six patient groups would have offered a more isolated effect of cinnamon.

These demographic and dietary differences may not correlate with the same results in western populations. Of note, parameters for insulin sensitivity, glucose tolerance, changes in blood insulin levels, and actual A1C values were not reported in the study. Furthermore, the researchers did not explain why significant reductions in glucose levels continued in group 1 after the 20-day washout period. This may be merely a result of the small sample size.

The second prospective, randomized, double-blind, placebo-controlled trial involved 79 German patients with type 2 diabetes.[5] The objective was to evaluate the effects of aqueous cinnamon purified extract on fasting plasma glucose levels, A1C, and triglyceride, low-density lipoprotein, high-density lipoprotein, and total cholesterol levels. Mean baseline A1C values and fasting glucose levels were 6.79% and 161.28 mg/dl, respectively.

In this study, patients receiving treatment with diet and/or one or more oral antidiabetic agents were randomly assigned to receive either a capsule containing 112 mg of aqueous cinnamon extract (C. cassia, equivalent to 1 g of cinnamon) (33 patients) or an identical capsule containing placebo (32 patients) 3 times/day with meals for 4 months. Plasma glucose levels were obtained after an overnight fasting state at baseline and at the end of the 4-month study period.

Fourteen of the 79 patients were excluded due to irregular adherence with the study agent (one patient), weight change of 5% or greater (two), serious disease (four), or withdrawal of consent (seven). Of the 65 patients evaluated at baseline (44 men, 21 women), no significant differences were observed regarding sex, time since diagnosis of type 2 diabetes, age, body mass index, or waist circumference. Diet and exercise were the only treatment in 23.1% of these patients. By comparison, 27.7% were concurrently receiving metformin, 12.3% sulfonylureas, 4.6% meglitinides, 1.5% thiazolidinediones, and 30.8% oral combination antidiabetic agents. Furthermore, 49.2% and 20%, respectively, received concurrent drug therapy for hypertension and hyperlipidemia. Compliance was measured by pill count and a diary in which patients reported any days they missed taking one or more capsules.

Only data from the 65 patients were included in the final evaluation. Patients receiving cinnamon showed a significant mean B1 SD percentage reduction in fasting plasma glucose level of 10.3% B1 13.2% compared with 3.37% ± 14.2% in those receiving placebo (p=0.046). No significant differences were observed regarding A1C values ( Table 2 ). No adverse effects were reported.

Although the researchers concluded that cinnamon extract appears to be moderately effective in reducing fasting plasma glucose levels in patients with poorly controlled type 2 diabetes, the study has several limiting factors. The first limitation was the small sample size (65 patients). In addition, the researchers measured glucose levels only twice throughout the study; more frequent measurements could have helped determine actual trends of cinnamon effects. Also, baseline A1C levels of the study patients were already at goal before the cinnamon intervention. Furthermore, diet was not standardized in the trial.

The third clinical trial was a 6-week, placebo-controlled intervention study that investigated the potential benefits of cinnamon in 25 postmenopausal patients diagnosed with type 2 diabetes.[13] The study was neither randomized nor blinded. All patients were in stable condition, with their diabetes controlled either by diet or by oral antidiabetic therapy for at least 3 months with sulfonylureas, metformin, thiazolidinediones, or any combination of these oral agents. Thirteen patients were assigned to receive cinnamon (C. cassia) 1.5 g once/day and 12 to receive placebo.

Patients were monitored at week 0 (baseline), after week 2, and at week 6 for whole-body insulin sensitivity or oral glucose tolerance, A1C value, and blood lipid profiles. They were instructed to maintain their normal diet, physical activity program, and drug therapy regimen. They were also instructed not to consume foods containing cinnamon or engage in heavy physical exercise for at least 3 days before each oral glucose tolerance test. Records of dietary food intake were obtained for standardization before the study began. Before each test, all patients received the same standardized meal, which consisted of 60% of energy as carbohydrate, 28% of energy as fat, and 12% of energy as protein.

After 6 weeks of cinnamon intervention, no significant differences were noted in A1C or fasting glucose levels in patients receiving cinnamon versus placebo ( Table 2 ). Insulin resistance and sensitivity indexes did not differ between the groups, and no significant differences were observed between results at baseline and 6 weeks of treatment. No adverse effects were reported.

The researchers concluded that supplementation with cinnamon 1.5 g/day did not improve fasting plasma glucose concentration or whole-body oral glucose tolerance in postmenopausal women with type 2 diabetes. However, the study was not blinded or randomized, and it was limited to postmenopausal women. Another limiting factor was the small sample size (25 patients). In addition, the study duration may have been too short to allow for accurate interpretation of the A1C while receiving cinnamon. The ADA recommends a 2-3 month interval between A1C measurements.[1] Also, the baseline fasting plasma glucose levels of the study patients were much lower than those of patients in the previous two studies.


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