THURSDAY, Oct. 25 (HealthDay News) -- Healthy middle-aged women do not benefit from taking resveratrol supplements, new study shows. Resveratrol is the ingredient in red wine thought to improve insulin sensitivity, reduce the risk of heart disease and increase longevity.

Although resveratrol supplementation doesn't appear to help these women, it's possible that another ingredient in red wine may provide a health benefit, the researchers from the Washington University School of Medicine in St. Louis pointed out.

"Resveratrol supplements have become popular because studies in cell systems and rodents show that resveratrol can improve metabolic function and prevent or reverse certain health problems like diabetes, heart disease and even cancer," senior investigator Dr. Samuel Klein, director of Washington University's Center for Human Nutrition, said in a university news release. "But our data demonstrate that resveratrol supplementation does not have metabolic benefits in relatively healthy, middle-aged women."

The study involved 29 postmenopausal women who were generally healthy and did not have type 2 diabetes. The researchers had 15 of the women take a 75 milligram over-the-counter resveratrol supplement daily for 12 weeks. They noted that this was the equivalent of drinking over two gallons of red wine. The insulin sensitivity and metabolic response of these women was then compared to 14 other women who took a inactive placebo pill over the course of the study.

"It's the most sensitive approach we have for evaluating insulin action in people," said Klein. "And we were unable to detect any effect of resveratrol. In addition, we took small samples of muscle and fat tissue from these women to look for possible effects of resveratrol in the body's cells, and again, we could not find any changes in the signaling pathways involved in metabolism."

Previous studies suggested drinking red wine lowers the risk for certain health problems, prompting many people to buy resveratrol supplements to get the benefits of the ingredient without drinking large amounts of alcohol. Annual sales of resveratrol supplements in the United States have reached $30 million, the researchers noted in the news release.

Based on the new findings, however, the study authors concluded that the benefits of resveratrol may be limited to people who already have a metabolic condition.

"Few studies have evaluated the effects of resveratrol in people," added Klein. "Those studies were conducted in people with diabetes, older adults with impaired glucose tolerance or obese people who had more metabolic problems than the women we studied. So it is possible that resveratrol could have beneficial effects in people who are more metabolically abnormal than the [healthy women] who participated in the study," he explained in the news release.

"The purpose of our study was not to identify the active ingredient in red wine that improves health but to determine whether supplementation with resveratrol has independent, metabolic effects in relatively healthy people," said Klein. "We were unable to detect a metabolic benefit of resveratrol supplementation in our study population, but this does not preclude the possibility that resveratrol could have a synergistic effect when combined with other compounds in red wine."

The study was published in the Oct. 25 online edition of the journal Cell Metabolism.

More information

The U.S. National Cancer Institute has more about resveratrol and cancer prevention.