Friday, May 16, 2014

Why I’m Not Surprised that Dietary Resveratrol may not be Associated with Living Longer

Headlines, supplements and nutrition fads often leap way ahead of the research. That’s why I’m not surprised at the results of the latest and best study done to date on dietary resveratrol. Resveratrol is a “phytochemical” – a naturally occurring chemical in plants – found in the skin of red grapes (and subsequently red wine), peanuts, and cocoa. This most recent study showed that resveratrol from foods and beverages did not correlate with a lower chance of dying, cancer risk, heart disease risk, or with markers of inflammation.
The study: Older adults in the Chianti region (a big red wine making area) were followed for 9 years. The participants reported on their dietary intake regularly during those years. The researchers and study geriatricians evaluated the participants’ dietary intake of resveratrol, their urinary resveratrol (which has been found to correlate with dietary intake), the diseases they had, and markers of inflammation over the course of the study. They found that the people who had the highest resveratrol intake were just as likely to suffer from heart disease and cancer and to die as the people with the lowest intake.  There were no differences in markers of inflammation between the groups.

Here’s why I am not surprised by the findings:

  • Many of the previous studies that have shown benefits from resveratrol have been done in rats. Rats are not humans – a fact often lost on those humans reporting on scientific studies and supplement makers.
  • Both the rat and the human studies have used large doses of resveratrol from supplements – far more than we can possibly get from foods and beverages.
  • Some human studies have shown benefits - and some have not. The ones that have shown benefits often look at “markers of inflammation” and show that resveratrol supplements lowered these markers. One study showed that resveratrol supplements lowered stiffness in the arteries of women. But, just lowering a marker of something bad does not necessarily translate into improved health or a lower chance of dying. I see this kind of data on markers of health all the time and they are useful but we shouldn’t base our recommendations off of them. These kinds of studies need to lead to studies that look at the outcomes that really matter – like disease, disability, and death.
  • Some human studies have shown no benefit and even harm from resveratrol supplements. One study showed that when older men were randomized to get either a 250 mg resveratrol supplement or a placebo for eight weeks during an intense exercise program, the men on the supplement did not experience the positive changes in cholesterol levels or in blood flow that the men on the placebo did. In other words, the supplements actually impaired some of the benefits of exercise rather than improving them as expected!

Keep in mind that this most recent study is also not the last word on resveratrol. While it was a strong, well-designed study, all studies have limitations. I also would not have been surprised if the study had shown that dietary resveratrol was beneficial because, again, the previous research had gone both ways. Neither outcome would have been surprising. 

Beth Kitchin, PhD, RDN
Assistant Professor, Nutrition Sciences
University of Alabama at Birmingham

Semba RD, Ferrucci L,  Bartali B, Urpi-Sarda M, Zamora-Ros R, Sun K, et al. Resveratrol levels and all-cause mortality in older community-dwelling adults. JAMA. 2014; published online May 12, 2014.

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