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Two recent research studies on humans indicate that resveratrol, a chemical found in red wine and peanuts, increases insulin sensitivity in older and obese people. A third study, done on mice, shows that resveratrol may someday become a powerful tool in therapies directed at macular degeneration and other retinal maladies.
The two studies on people, conducted by the Albert Einstein College of Medicine at Yeshiva University in New York City, involved overweight or older (average age 72) subjects. People often develop resistance to the effects of insulin as they age or put on weight. This resistance, called impaired glucose tolerance (IGT), is a precursor to diabetes and often shows up in people who have been diagnosed with pre-diabetes.
The research on older patients, led by Jill Crandall, MD, an associate professor of clinical medicine and director of the Diabetes Clinical Trials Unit at Einstein, was a small pilot study designed to see if resveratrol had any effects on insulin resistance brought on by aging. The 10 study patients with IGT who took concentrated amounts of resveratrol-much higher than the amounts found in food or drink-all showed improved insulin sensitivity and lower post-meal levels of blood glucose.
The resveratrol supplement used in the study, Transmax, is produced by Biotivia LLC of New York, a manufacturer of resveratrol-based health supplements (www.biotivia.com).
Given the small number of study subjects, Crandall said, the pilot study results are preliminary and will need to be confirmed in larger numbers of patients.
"However, we are encouraged by these findings and plan to conduct additional studies to further explore the potential utility of resveratrol in improving glucose metabolism."
Meredith Hawkins, MD, a professor of medicine and director of the Global Diabetes Initiative at Einstein, conducted a related study that explored the effects of resveratrol on overweight middle-aged subjects with insulin resistance. She reported a 40 percent increase in insulin sensitivity among the subjects receiving the chemical supplement.
A third, unrelated study on mice at the Washington University School of Medicine in St. Louis, showed that resveratrol was able to stop blood vessel growth in the retinas of mice whose eyes had been damaged by lasers. Those injuries and subsequent attempts by the body to repair them mimic what happens in macular degeneration, a potential long-term side effect of diabetes. Inhibiting the growth of the blood vessels, which tend to be weak and "leaky," prevents further damage to the retina.
If these effects are duplicated in later studies on human subjects, resveratrol could become a therapy for slowing down or even stopping macular degeneration.
The study on mice also revealed that resveratrol may work in more complex ways than scientists had previously thought. Earlier studies on laboratory animals had shown that the chemical stimulates proteins called sirtuins, which have a beneficial effect on longevity and metabolism. In the Washington University study, researchers deactivated sirtuin activity to see if that would prevent resveratrol from working.
When it didn't, they realized that another factor might be at work. According to Rajendra Apte, a retinal surgeon at the school who led the study, another protein, called elongation factor-2 kinase, is involved in resveratrol's ability to inhibit blood vessel growth. That finding confirms other researchers' suspicions that resveratrol may work along multiple paths.