Ginkgo Supplementation and Insulin Resistance (October 15, 2007) By Jeremy Appleton, ND

New research on Ginkgo biloba suggests that the popular herb could be associated with resistance to insulin in healthy individuals, theoretically increasing the risk of type 2 (adult-onset) diabetes and a related condition known as Syndrome X. The small clinical trial, published this month in the Journal of Clinical Pharmacology, examined the effects of ginkgo supplementation on secretion of insulin by the pancreas and on blood levels of glucose.

 

The 20 participants in the trial, all healthy adults, were given 120 mg of concentrated, standardized ginkgo extract (containing 24% ginkgo flavone glycosides and 6% terpenes) for three months. A comparison of measurements taken at the beginning of the trial and at the end of three months of ginkgo supplementation, found increased blood levels of insulin. However, blood levels of glucose were not affected. (Insulin is responsible for removing glucose from the blood and delivering it to tissues, such as the brain and muscle, where it is used for fuel. When insulin is secreted, glucose levels normally go down.)

 

This trial?s finding of elevated insulin, coupled with glucose levels that did not change, suggests that the participants may have developed an insensitivity to insulin. It is a potential concern because insulin insensitivity is a feature of Syndrome X (a frequently seen combination of diabetes, obesity, high blood pressure, and insulin resistance) and by itself may be a precursor to type 2 diabetes.

 

In this trial, ginkgo supplementation may have stimulated cells in the pancreas that secrete insulin (beta cells). However, increased insulin secretion is only beneficial if the insulin effectively removes glucose from the blood. In the absence of an effect on blood glucose, the elevated insulin levels suggest that the pancreas may have been reacting to a lack of effect by insulin (insulin insensitivity).

 

Putting the Trial Into Context

 

The findings of this preliminary trial are merely suggestive, particularly in light of the trial?s short duration. A longer trial may have found a more balanced response to insulin increases, or may have found that the increases themselves were transient. This trial does not prove that ginkgo causes insulin insensitivity, or that long-term ginkgo supplementation increases the risk for any disease.

 

Moreover, the results of this trial do not fit neatly with what is known about ginkgo. In another preliminary trial, supplementation with ginkgo extract led to positive effects on circulation in people with type 1 (insulin-dependent) diabetes.2 Research in animals3 4 and humans5 strongly suggests that ginkgo is protective against complications of diabetes and pancreatitis (inflammation of the pancreas).

 

Larger and more rigorously designed clinical trials of ginkgo supplementation have found no significant adverse effects after as many as 12 months of supplementation.6 The author of the new trial, George Kudolo, Ph.D., of the University of Texas, admits that the implications of his findings are ?speculative? and that further studies are needed to ?provide definitive information on changes of whole-body insulin sensitivity.

 

According to the German Commission E, an authority on the safety and therapeutic applications of herbal medicines, Ginkgo biloba extract is essentially devoid of any serious side effects.7 It has been used medicinally for centuries and is currently used safely by millions of people throughout the Unites States and Europe. The results of the new trial are intriguing and warrant further research. However, they do not provide enough evidence to meaningfully dispute the long-term safety of this herbal medicine.

 

Source:

1. Kudolo GB. The effect of 3-month ingestion of Ginkgo biloba extract on pancreatic ?-cell function in response to glucose loading in normal glucose-tolerant individuals. J Clin Pharmacol 2000;40:647?54.
2. Balashova TS, Kubatiev AA. [Effects of tanakan on blood lipid peroxidation and platelet aggregation properties in patients with insulin-dependent diabetes mellitus]. Ter Arkh 1998;70:49?54 [in Russian].
3. Doly M, Droy-Lefaix MT, Braquet P. Oxidative stress in diabetic retina. EXS 1992;62:299?307.
4. Soybir G, Koksoy F, Ekiz F, et al. The effects of free oxygen radical scavenger and platelet-activating factor antagonist agents in experimental acute pancreatitis. Pancreas 1999;19:143?9.
5. Lanthony P, Cosson JP. [The course of color vision in early diabetic retinopathy treated with Ginkgo biloba extract. A preliminary double-blind versus placebo study]. J Fr Ophtalmol 1988;11:671?4 [in French].
6. Le Bars PL, Katz MM, Berman N, et al. A placebo-controlled, double-blind, randomized trial of an extract of Ginkgo biloba for dementia. North American EGb Study Group. JAMA 1997;278:1327?32.
7. Blumenthal M, Busse WR, Goldberg A, et al. (eds). The Complete Commission E Monographs: Therapeutic Guide to Herbal Medicines. Boston, MA: Integrative Medicine Communications, 1998, 136?8.

Jeremy Appleton, ND, is a naturopathic physician, writer, and lecturer in the field of evidence-based complementary and alternative medicine. Dr. Appleton is an adjunct professor of nutrition at National College of Naturopathic Medicine and Senior Science Writer at Healthnotes.