Considering resveratrol's promising cancer-fighting, anti-diabetic, and life-extending benefits, all evidenced in labs, researchers expected supplements of the antioxidant to have a positive impact on exercise. However, a new study suggests that the opposite is true: Resveratrol actually limited test subjects' ability to improve their cardiovascular health by working out.

Found in foods like peanuts, soy, grapes, and red wine, resveratrol has been shown to improve oxygen uptake from exercise in rodents, but that all changed with a recent study on humans by Lasse Gliemann, a Ph.D. student at the University of Copenhagen. Participants in the experiment were all males over the age of 65, and consumed 250mg of resveratrol before undergoing a battery of physically exhausting tests over a period of eight weeks. The results showed that the men who had taken a placebo had better oxygen uptake – some 45 percent higher – over the resveratrol group. They also achieved greater improvements in blood pressure and blood cholesterol.

"Taking resveratrol supplements might not be a great idea if you're preparing for an upcoming Ironman," says Gliemann, who isn't sure why the supplement impacts humans differently. Part of the reason may be in the high dosage, or because it is a supplement, rather than a naturally occurring source of the antioxidant. But Gliemann says this shouldn't push athletes on or off a daily glass of wine: "In order to match the 250mg of resveratrol used in the study with red wine alone, you'd have to drink nearly a case a day."