Resveratrol is a substance found in the skin of grapes, red wine, purple grape juice, blueberries and cranberries, and some nuts. The quantities vary depending on the type of fruit or nut, its geographic origin, and, in the case of wine, grape fermentation time. Resveratrol is a stilbene, a class of polyphenic compound. Stilbenes are produced in plants in response to stress, injury, infection with fungi, or UV radiation. Resveratrol became interesting to scientists in 1992, when the “French Paradox” became known. The French Paradox is the observation that in France, despite high saturated fat consumption and cigarette smoking, mortality from cardiovascular disease is relatively low. It was speculated that regular consumption of red wine might be protective, so scientists began examining the compounds found in red wine. While results of studies on the benefits of resveratrol have been inconsistent in terms of cardiovascular disease risk reduction, there is mounting evidence of a variety of beneficial and protective effects of this compound. These benefits include the inhibition of cancer in animal models, the extension of lifespan in animal and cell models, and anti-inflammatory properties.
Cancer prevention is a complex topic. Some compounds become carcinogenic upon metabolism by enzymes known as cytochrome P450 enzymes. Resveratrol may help prevent cancer development by inhibiting the activity of these enzymes. Another way resveratrol may prevent cancer is by causing cancer cell cycle arrest and even cell death (apoptosis) when added to certain cancer cell cultures. Cell proliferation that leads to cancer can be caused by inflammatory enzymes that are inhibited by resveratrol. Finally, resveratrol has been found to inhibit angiogenesis, or the development of new blood vessels that feed tumors. However, all of these activities are confirmed only in vitro, or in laboratory conditions, at doses higher than would be consumed by people orally. More research is needed to clearly define the potential benefits in vivo, or in humans.
Many people have heard that moderate red wine consumption can lead to reductions in cardiovascular disease risk. Red wine contains resveratrol and flavonoids, which are antioxidants with anti-inflammatory properties. What is not known yet is if the polyphenols from red wine add any protective effect beyond the protection offered by moderate use of alcoholic beverages in general. There are many confounding factors, such as drinking other kinds of alcohol without resveratrol, socioeconomic and lifestyle factors, and dietary habits, all of which may affect cardiovascular risk.
However, in laboratory tests resveratrol has been shown to offer cardioprotective effects such as prevention of blood clotting, relaxation of blood vessels, and the inhibition of inflammatory enzymes, all of which make resveratrol highly interesting to scientists studying the effects of resveratrol in humans. The problem with recommending resveratrol is that the amounts of the compound found in moderate consumption of red wine, eg, 1-2 glasses of wine per day, have not been shown to be sufficient to produce consistent cardio protective effects in humans. There seems to be more compelling evidence of resveratrol’s cancer preventive effects, particularly in terms of breast, prostate, stomach, colon, pancreatic, and thyroid cancers. Interestingly, resveratrol seems to have no effect on lung cancer. Clinical trials are underway to determine the effects of oral administration of resveratrol in humans, both in terms of prevention and treatment of cancer. Unfortunately, preliminary results to date suggest that dietary intake of resveratrol does not provide enough of the compound to offer protective effects.
In addition to the dietary sources listed above, resveratrol is available as a dietary supplement. The supplements are made from Polygonum cuspidatum, or red wine or red grape extracts. The supplements may contain anywhere from 10-50 mg of resveratrol. However, recommended doses are unavailable since effective doses for disease risk reduction in humans are not yet known. In clinical trials, doses of up to 5 grams of resveratrol daily showed no adverse effects in humans. Due to its blood clotting inhibitive properties, people on anticoagulant drugs should avoid taking taking resveratrol. Since no safe level of alcohol has been established for pregnant women, pregnant women should not consume wine as a way of obtaining resveratrol in their diets.