A recent meta-analysis has shown that cinnamon can reduce blood glucose, total and LDL cholesterol, and increase HDL cholesterol in type 2 diabetes.

The researchers had published a previous meta-analysis that was unable to show any benefit from cinnamon, but repeated the exercise because there have been several randomised controlled trials performed since the last review.

Studies considered eligible for the meta-analysis were randomised controlled trials of patients with type 2 diabetes that evaluated the use of oral cinnamon supplementation in any dose or form, regardless of any additional intervention for diabetes. Trials had to have reported data on at least one of the following endpoints: HbA1c, fasting glucose, total cholesterol, LDL cholesterol, HDL cholesterol or triglycerides.

 Ten studies, covering 543 patients, using cinnamon doses of 120 mg/d  to 6 g/d for 4 to 18 weeks met the criteria for inclusion. Although all were recent, most were small studies with only one having more than 100 patients in total. The pooled patient populations were different for each outcome measure, but varied between 188 and 254.

Although there are concerns that cinnamon could potentially cause allergy, liver toxicity and thrombocytopaenia, no side effects from supplementation were reported in any of the trials.

The pooled results of the analysis showed a significant reduction in fasting blood glucose, total cholesterol, and LDL cholesterol and a rise in HDL cholesterol levels.

The reductions in fasting plasma glucose levels (-24.59 mg/dL) were less than those reported elsewhere for metformin monotherapy (-58 mg/dL) but more than those reported for the newer oral agents, such as sitagliptin (-16 to -21 mg/dL).

Cinnamon reduced LDL cholesterol and triglyceride levels by around 9.4 and 29.6 mg/dL respectively.

The lipid-lowering drugs pravastatin and gemfibrozil have been shown in previous studies to result in reductions of around 50 mg/dL (26%) and 50 mg/dL (31%), respectively. Cinnamon also increased HDL cholesterol levels by 1.66 mg/dL.

Despite the reduction in fasting blood glucose, there was no evidence of a significant reduction in HbA1c overall, or at any time in any of the studies analysed.

In the past decade there has been a resurgence of interest in the medicinal properties of the spice, when the active principle cinnamaldehyde was isolated. This compound has been shown to promote insulin release and enhance insulin sensitivity.

In animal studies, cinnemaldehyde has been shown to increase expression of peroxisome proliferator-activated receptors. These are the transcriptional factors involved in the regulation of insulin resistance and adipogenesis. Altering these factors is the mechanism by which glitazones exert their antidiabetic effect.

Despite strong public interest in natural products for treating diabetes, the American Diabetes Association does not endorse their use. This is because of insufficient clinical data on safety, and clinical efficacy, and the lack of standardised formulations.

In the UK, cinnamon as a flavouring is strongly associated with Christmas and winter foods, especially cakes, fruit pies and puddings.

As GPs we are often asked about alternative treatments for type 2 diabetes. This meta-analysis suggests that although we cannot yet formally endorse the use of cinnamon, our annual Christmas treats may not be quite as bad for us as we had thought!

Dr Matthew Lockyer