Review question:

What are the effects of cinnamon in patients with diabetes mellitus?

Nursing Implications:

Long-term control of blood glucose is essential to reduce the risk of developing complications such as retinopathy, neuropathy, nephropathy, cardio-vascular disease and stroke in individuals with diabetes mellitus. Healthcare professionals need to be aware of the risks and benefits of any potential intervention that claims to have the ability to control blood glucose levels, such as cinnamon, especially in the presence of an increasing variety of over the counter products. There is therefore a need to review the available evidence of their effectiveness in diabetes mellitus to inform healthcare policies and practice.

Study Characteristics:

The evidence included in this summary is from a Cochrane systematic review containing 10 prospective, parallel group design randomised controlled trials (RCTs) involving 577 adult participants. All but one study involved participants with a diagnosis of Type 2 diabetes mellitus; the remaining study involved participants with Type 1 diabetes mellitus. The mean age of participants ranged from 52-63 years, with one trial involving adolescents with a mean age of 15 years. The setting was predominantly university outpatient clinics in a range of geographical locations including the USA (4 trials), UK (1trial), Pakistan (2 trials), Germany (1 trial), Thailand (1 trial) and the Netherlands (1 trial). All studies used monopreparations of cinnamon (primarily Cinnamomum cassia) in tablet or capsule form, at an average daily dose of 2g, for a mean period of 11 weeks. Comparisons consisted of; placebo, no treatment or active medication such as insulin, oral hypoglycaemic agents or other herbal/nutritional preparation. Studies that used combination preparations of cinnamon or failed to meet the criteria for type 1 or type 2 diabetes mellitus were excluded from the review. The primary outcomes of interest focused on fasting blood glucose levels (FBGL); postprandial glucose (PPG) levels; and adverse events with secondary outcomes including Glycosylated haemoglobin A1c (HbA1c); serum insulin; insulin sensitivity; Health-related quality of life (HRQoL); morbidity; and costs. Meta-analysis of trials was undertaken where possible.

The methodological quality of the included studies varied with two of the trials being assessed as having moderate risk of bias and a further five trials having a high risk of bias. Only three explicitly reported the randomisation method, and two reported concealed allocation. Other quality items such as blinding, intention-to-treat analysis (ITT) and completeness of follow-up were incompletely reported in some of the studies.

Summary of Key Evidence:

No statistically significant difference was found between the cinnamon intervention and control groups with regards to the fasting blood sugar level (8 trials), PPG (1 trial) adverse events (4 trials), HbA1c (6 trials) serum insulin (2 trials) or insulin sensitivity (2 trials). HRQoL, morbidity and costs as endpoints were not explored by any of the included studies.

Best Practice Recommendations:

The findings of this review indicate that the use of cinnamon in diabetes mellitus is no more effective in reducing blood glucose levels or HbA1c than a placebo, alternative active medication, or no treatment at all.

There is therefore a need for more rigorous research that investigates not only the long-term benefits and risks of the use of cinnamon for diabetes mellitus, but also how it affects HRQoL and the complications of diabetes mellitus.

Summary Author

Lesley Andrews, RN, SPQ (Renal), BSc, PGDip, PGCert
School of Nursing, Midwifery and Health
University of Stirling
Scotland

A member of the Cochrane Nursing Care Field (CNCF)