Resveratrol is an ingredient found in the skin of grapes that is thought to hold many health benefits. It may, in fact, but new research suggests it's not a miracle ingredient for everyone.
Researchers at Washington University School of Medicine in St. Louis say resveratrol may improve insulin sensitivity, reduce risk of heart disease and increase longevity, but it does not appear to offer these benefits in healthy women.
Admittedly, the study is a small one. It involved 29 post-menopausal women who did not have type 2 diabetes and who were reasonably healthy. For 12 weeks, half took an over-the-counter resveratrol supplement, and the rest got a placebo, or sugar pill.
In supplement form
"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," said senior investigator Samuel Klein, MD, director of Washington University's Center for Human Nutrition. "But our data demonstrate that resveratrol supplementation does not have metabolic benefits in relatively healthy, middle-aged women."
The study may call into question the assumption, derived from previous research, that drinking red wine or taking resveratrol supplements lowers the risk of health problems. That may be because previous studies have mostly measured resveratrol's effects on specific parts of the population.
"Few studies have evaluated the effects of resveratrol in people," Klein said. "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 subjects who participated in the study."
Many people who have heard about red wine's health benefits but don't drink alcohol have purchased resveratrol supplements to get the benefits. Resveratrol has become a sizable segment of the supplement market, accounting for about $30 million in annual sales. But the research suggests that if you are a healthy person, you might not need them.
As part of the study, Klein and his colleagues gave 15 post-menopausal women 75 milligrams of resveratrol daily, the same amount they'd get from drinking 8 liters of red wine, and compared their insulin sensitivity to 14 others who took a placebo.
The team measured the women's sensitivity to insulin and the rate of glucose uptake in their muscles, infusing insulin into their bodies and measuring their metabolic response to different doses.
"It's the most sensitive approach we have for evaluating insulin action in people," he said. "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."
The researchers aren't ruling out that some other ingredient in red wine is providing a heart health benefit. They just don't know what it is.
"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," Klein said.