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How common herbal supplements affect diabetes

Many patients at risk for, or who have developed, diabetes turn to over-the-counter herbal supplements to prevent or control their disease. Unfortunately, quality clinical data is sparse. In this column, I’ll briefly review the data on five common herbal supplements used for diabetes.

Well-known supplements

Cinnamon is probably the most studied, most publicized and most used herbal supplement for diabetes. As one might expect, the data on the benefit of cinnamon in diabetes is not entirely compelling. One study randomly assigned patients with type 2 diabetes to various daily doses (1, 2 or 3 g/day) of cinnamon or placebo for 40 days. At the end of the study, those on any dose of cinnamon had a reduction in fasting glucose between 18% and 29% vs. placebo. Another randomized study compared 3 g/day of cinnamon with placebo in 79 patients over 4 months. At the end of the trial, fasting and postprandial glucose were reduced in the cinnamon group, but there was no significant change in HbA1c. Two other studies involving patients with type 2 diabetes found significant reductions in HbA1c with administration of 1 g to 2 g of cinnamon per day. Finally, there have been several other trials that showed no hypoglycemic benefit from cinnamon administration, although some of these trials were done in healthy volunteers or in those with type 1 diabetes. In the above trials, there is better evidence that cinnamon may have a beneficial effect on fasting or postprandial glucose as compared with a beneficial effect on HbA1c. Most of these trials were not rigorously designed and exhibited some potential for bias. Adverse effects in all of the trials were rare, and those that did develop usually involved gastrointestinal symptoms.

Green tea has a number of purported benefits, including hypoglycemic benefits. One trial involved 66 patients with diabetes who took green tea extract daily (control group did not take any supplement). After the study, fasting glucose and HbA1c were reduced to a similar extent in both the treatment and control groups. Three other small randomized, placebo-controlled studies in patients with diabetes showed no difference in changes in glucose or HbA1c as compared with placebo. Thus, despite the use of various doses and formulations of green tea, there are no data to indicate that it has any benefit in the treatment of diabetes.

Lack of effect on glucose

Bitter melon, consumed as a vegetable or flavoring, has been promoted as having antihyperglycemic benefits. To-date, studies of bitter melon’s effects on diabetes have been very small. One randomized trial included 50 patients with diabetes assigned to bitter melon or placebo. After 4 weeks, there was no change in glucose with the addition of bitter melon. A similar trial in 40 patients found no difference in glucose or HbA1c after 3 months of treatment. One multicenter, randomized trial compared bitter melon alone (in three different daily doses) and bitter melon added to metformin. After 4 weeks, the group receiving the highest dose of bitter melon and the group on bitter melon and metformin had a significant reduction in fructosamine. There was no significant change in the two groups receiving lower doses of bitter melon.

James R. Taylor

Fenugreek has been studied in four human trials involving diabetes. One study involving 25 patients with type 2 diabetes found no effect of fenugreek on glucose. However, a slightly larger trial involving 60 patients with type 2 diabetes randomly assigned to fenugreek or placebo for 3 months found significant reductions in fasting and postprandial glucose. A few small studies in healthy volunteers also showed improvements in glucose with the use of fenugreek.

In summary, there are limited data to support the use of these herbal supplements for diabetes. However, no apparent serious adverse effects have been reported, so there may be no harm in patients using them.

With the increasing use of herbal supplements, large, well-designed trials are warranted to confirm the role, if any, of these agents.

References:

James R. Taylor, PharmD, CDE, is a clinical associate professor in the department of pharmacy practice at the University of Florida, Gainesville. He can be reached at University of Florida, College of Pharmacy, P.O. Box 100486, Gainesville, FL 32610-0486; email: jtaylor@cop.ufl.edu.

Deng R. Recent Pat Food Nutr Agric. 2012;4:50-60.