So you've been feeling virtuous quaffing red wine, nibbling on dark chocolate and popping grapes, thinking you're reaping the life-extending, disease-fighting, health-promoting benefits of resveratrol. You'll need to think again, suggests a new study, which finds that high levels of resveratrol consumed as part of a regular diet are not linked to lower levels of cancer, cardiovascular disease or inflammation, and do not appear to prolong life.
The latest research on the promising polyphenol was conducted on the senior population of two villages in the Chianti region of Italy -- 783 men and women 65 and older whose health and resveratrol intake was tracked between 1998 to 2009. The study was published Monday in JAMA Internal Medicine.
Avoiding the pitfalls of asking study participants to record or recall their daily intake, the researchers regularly gathered specimens of subjects' urine and tested them for levels of resveratrol metabolites. Fewer than 1% of the study population took vitamin, mineral or herbal supplements of any kind, so researchers could be pretty sure that byproducts of resveratrol were the result of food and drink consumed, not from pills. As might be expected in one of Italy's most prolific wine-producing regions, red wine was a regular feature in most subjects' daily diets.
Of the study's 783 men and women, just over one-third died during the nine-year study. About 27% of those healthy to begin with developed cardiovascular disease, and 4.6% developed cancer. But whether a study participant consumed high levels of resveratrol or none at all, the study revealed no differences in rates of cancer, cardiovascular disease, death or inflammation.
The latest research was led by Johns Hopkins University opthamologist and public health specialist Dr. Richard D. Semba.
On first glance, the study would seem to dash hopes for resveratrol, a plant extract that National Institutes of Health researcher Rafael deCabo, who was not involved in the current study, calls "a super-exciting compound." But researchers have long suspected -- and, in fact, found in many studies -- that it'll take a lot more resveratrol than can be consumed in food to influence such surrogate measures of health and longevity as C-reactive protein, a marker of inflammation, or glucose control and insulin sensitivity.
Other studies finding health benefits to resveratrol supplementation have been conducted on people with established health conditions, including obesity and diabetes. Though a typical proportion of participants in the current study already were sick when they were recruited, they were a small minority. Most of those in the Chianti study were aging but healthy. And for them, consumed resveratrol didn't help.
So, as with many agents found in nature or synthesized in a lab, resveratrol is probably only helpful in doses higher than can practically be consumed (and safe in doses that have not yet been determined). And resveratrol may be better at treating disease than it is at preventing it.
"The levels of Resveratrol in the diet are negligible compared to the levels shown to work in mice and humans," said Harvard University researcher David Sinclair, who has pioneered much of the research on resveratrol and other agents that activate the same "sirtuin pathway" and potentially extend lifespan.
Sinclair says the Chianti study certainly casts doubt on a central tenet of the "French paradox" -- the surmise that it is the resveratrol in red wine consumed by the French that has kept cardiovascular disease relatively low in a country where saturated fat is plentifully consumed. But the study does not extinguish hopes that "resveratrol or more potent molecules like it will make effective drugs," said Sinclair, who was not involved in the Chianti study.
"We’re becoming more aware that the effects of resveratrol are pretty much context dependent: If you have a challenge or disease, resveratrol seems to have a positive effect," said researcher Rafael deCabo. But it may not be the "primary prevention drug" that many health-conscious Americans had hoped.
Americans already spend some $30 million on resveratrol supplements, ranging in potency to that found in a few glasses of red wine to doses that multiply that hundreds of time over. But the authors of the current study note that although dietary doses may be ineffective at prolonging life, the safety of higher doses is far from established.
"There are no data concerning its safety in high doses, or for long-term supplementation in older people, who often...are taking multiple medications," they wrote.
"We need to thoroughly investigate its effects in humans and what its complications may be," DeCabo said in an interview.
"It’s a super-exciting compound, but still we need to learn a lot more about the basic biology of it and possible complications" for those taking it, he said.