Reference
Allen RW, Schwartzman E, Baker WL, Coleman CI, Phung OJ. Cinnamon use in type 2 diabetes: an updated systematic review and meta-analysis. Ann Fam Med. 2013;11(5):452-459.
Design
A meta-analysis was performed on randomized controlled trials (RCTs) that provided data on the effect of cinnamon (Cinnamomum spp) on type-2 diabetes and were published before February 2012. Literature searches identified 83 possible studies for inclusion, of which 10 were included in this analysis.
Participants
The 10 RCTs selected included a total of 543 patients with type-2 diabetes, 254 of whom received cinnamon in their respective trial.
Study Medication and Dosage
There was considerable variability in the amount of cinnamon used and the duration of the trials included in this meta-analysis. Cinnamon doses ranged from a low of 120 mg per day up to 6 g per day. Study lengths were as short as 4 weeks and as long as 18 weeks.
Outcome Measures
The selected studies included at least one of the following biomarkers: glycated hemoglobin (A1c), fasting plasma glucose, total cholesterol, low-density lipoprotein cholesterol (LDL), high-density lipoprotein cholesterol (HDL), or triglycerides.
Key Findings
In this analysis, taking cinnamon was associated with significant decreases in fasting glucose, total cholesterol, LDL cholesterol, and triglycerides. HDL cholesterol increased significantly. No significant effect was seen on A1c.
Fasting glucose declined by about 25 mg/dL (–24.59 mg/dL; 95% confidence interval [CI]: –40.52 to –8.67 mg/dL). Total cholesterol dropped by nearly 16 points (–15.60 mg/dL; 95% CI: –29.76 to –1.44 mg/dL); LDL cholesterol by just over 9 (–9.42 mg/dL; 95% CI: –17.21 to –1.63 mg/dL); and triglycerides by nearly 30 points (–29.59 mg/dL; 95% CI: –48.27 to –10.91 mg/dL). HDL cholesterol increased slightly by a point and a half (1.66 mg/dL; 95% CI: 1.09 to 2.24 mg/dL).
Practice Implications
Will cinnamon prove useful in treating diabetes? This question has not been easy to answer.
The data from this current analysis suggest that taking cinnamon may have a slight but still possibly useful effect in treating type 2 diabetes. Even so, we need to remember that this is but one of a number of meta-analyses that have addressed this question and yielded somewhat mixed results.
In some studies, taking 1 g to 1.2 g of cinnamon per day has been associated with worsening blood parameters for diabetes; both fasting glucose and A1c values went up.1-3 Other studies have reported improvements in the same parameters, perhaps because they used higher doses of cinnamon (1g-6g/d).
This current analysis is promising; some of the effects are not only significant but clinically relevant. One of us commented in this journal about a 2012 meta-analysis by Akilen et al4 and expressed his opinion that although the impact of cinnamon was statistically significant, the results were, in his mind, not clinically so. In other words, the results might have been real but weren’t large enough to make much difference. In this current meta-analysis, while the A1c levels did not improve, cinnamon did have a positive impact on a range of biomarkers linked to cardiovascular disease (CVD). As reducing CVD risk is an important goal for diabetics, these findings are important.
Comparing the changes in CVD biomarkers reported here to changes from “established” therapies might put cinnamon’s value into perspective.
In this current meta-analysis, while the A1c levels did not improve, cinnamon did have a positive impact on a range of biomarkers linked to cardiovascular disease (CVD). As reducing CVD risk is an important goal for diabetics, these findings are important.
The 25-mg/dL drop in fasting blood sugar is about half the effect seen with metformin.5 Reductions associated with cinnamon in LDL cholesterol and triglyceride levels—9.4 mg/dL and 29.6 mg/dL, respectively—are also less than we see from the common lipid-lowering drugs, pravastatin and gemfibrozil, which reduce LDL cholesterol and triglyceride levels by approximately 50 mg/dL (26%) and 50 mg/dL (31%), respectively.6,7 Yet we must point out that using cinnamon to help control lipid panels does not cause any musculoskeletal side effects, such as aching or sore muscles, which are common with statin use.
That fasting blood sugar (FBS) responds to cinnamon without a significant change in A1c levels is difficult to understand. A1c levels reflect a 3-month average of both nighttime and postmeal levels. Lowering FBS should lower A1c levels. One might expect a 25-point decrease in fasting glucose levels to correspond with a 0.5% to 1% drop in A1C. This inconsistency in data leaves both of us baffled.
Even if there were some high postprandial glucose levels during the day, it would seem that there should be at least a 0.5% drop as a result of the long nighttime decreases in glucose levels. One possible explanation for this discrepancy is the length of the studies. Changes in A1c levels are typically measured at 3-month intervals. As some of the studies analyzed in this meta-analysis were only 4 weeks in length, perhaps the A1c readings in their data skewed the net results. Yet 6 of the 10 studies included in this meta-analysis were 12 or more weeks in length, and their results were no more significant for lower A1c levels.
Dosing amount may matter with cinnamon. Because blood sugar responses follow a hormetic curve, as mentioned before, lower doses (1-1.2 g/d) have been reported to increase blood sugar and cholesterol levels. While this may provide an explanation for the conflicting data, it presents us with a clinical challenge. Telling patients to take cinnamon might not be a good idea if they are required to consume a significant minimum quantity to prevent an unwanted increase in blood sugar.
None of these data suggest what we really want to know, which is how cinnamon might act in combination with other botanical extracts, vitamins, and minerals that could treat diabetes. The data also don’t address the question of how cinnamon might synergistically enhance a typical naturopathic protocol that includes a lower carbohydrate diet and encouragement and counseling for patients to exercise, sleep well, and reduce stress. Used in combination with cinnamon, these other substances that independently have hypoglycemic action may have additive or possibly synergistic effects with cinnamon. Our clinical experience certainly suggests that this does happen.
