The quality of evidence is downgraded by study limitations (unclear allocation concealment and selective reporting) and by imprecise results.
A Cochrane review included 10 RCTs with a total of 577 subjects to evaluate the effects of cinnamon in patients with type 1 and type 2 diabetes mellitus. The aromatic bark of the cinnamon tree is used in traditional Chinese and Ayurvedic medicine for its hypoglycaemic properties.
Oral monopreparations of cinnamon (predominantly Cinnamomum cassia) were administered at a mean dose of 2 g daily, for a period ranging from 4 to 16 weeks. The effect of cinnamon on fasting blood glucose level was inconclusive. No statistically significant difference in glycosylated haemoglobin A1c (HbA1c), serum insulin or postprandial glucose was found between cinnamon and control groups (Table 1). There were insufficient data to pool results for insulin sensitivity.
No trials reported health-related quality of life, morbidity, mortality or costs. Adverse reactions to oral cinnamon were infrequent and generally mild in nature.
| Outcome | No of participants (studies) | Assumed risk (control) | Corresponding risk (intervention) | Relative effect (95% CI) |
|---|---|---|---|---|
| HbA1c (follow-up 3 to 4 months) | 405 (6) | The mean HbA1c ranged across control groups from 6.8% to 8.8% | The mean HbA1c in the intervention groups was 0.3% lower to 0.2% higher | MD -0.1% (-0.3% to 0.2%) |
| Adverse reactions | 264 (4) | 0.82 (0.21 to 3.23) |
Some health agencies have warned against consuming high amounts of cassia bark, one of the four species of cinnamon, because of its coumarin content.
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