Ever since it became clear that resveratrol was a key regulator of energy metabolism and could increase the lifespan in some animal species, the market for resveratrol supplements has been increasing exponentially. More than $30 million is spent on resveratrol supplements each year in the US alone.
However, there are some things you should bear in mind before you jump on the resveratrol bandwagon.
Resveratrol supplements are not regulated by the FDA, which means their strength is unverified and the actual concentration of the compound is unknown. Supplements may contain anything from 250-500 mg. In addition, their efficacy in any field of action is unproven by scientific evidence.
Most supplements today are prepared from resveratrol sourced from Japanese knotweed (Polyphenum cuspidate) or kojo-kon. Other sources for this supplement are red grape extracts or red wine extracts.
At present, the optimal dosage in humans, if any, is unknown, because most of the experiments have been carried out in lower animals at extremely high concentrations of pure resveratrol. Many recommendations are for 2 g a day, but this is not confirmed by evidence. Scientists confirm that up to 5 g can be ingested as one dose, without adverse effects, but only one dose was administered. The effect of long-term administration of resveratrol at various doses is as yet unclear.
This is especially important in pregnant women, or during lactation. Moreover, it could adversely affect estrogen-sensitive cancers of the breast, endometrium or ovary, because of its mixed agonist-antagonist activity. It also inhibits some key enzymes which metabolize estrogens, and this could negatively affect oral contraceptive action.
Additionally, its action on platelet aggregation means that this compound may accentuate the anti-platelet effects of anticoagulant drugs, such as warfarin or Coumadin, clopidogrel (Plavix), dipyridamole (Persantine), and non-steroidal anti-inflammatory drugs (NSAIDs), including aspirin, naproxen and ibuprofen.
Even more importantly, it has been shown to minimize some favorable effects of exercise training in older men. Thus there was a greater increase in the maximal oxygen uptake in the placebo group than in the resveratrol group, as well as a lowered mean arterial blood pressure in the group on placebo, but not in the resveratrol group. Resveratrol supplementation was associated with lack of the expected favorable effects of exercise on blood cholesterol, LDL, HDL and triglyceride concentration. There was no change in other important markers of inflammation and cell adhesion which precede atherosclerosis.
All said and done, it may not be time to start taking resveratrol supplements yet. Food scientists point out that the free radical scavenging activity of resveratrol in red wine is much less than that of other polyphenols also present in red wine, like caffeic acid, as established in studies on cultured cells. A recent study which followed the health of almost 800 older people from a central wine-making region of Italy for almost two decades found no marked difference in death rates between those who had the lowest resveratrol levels and those with the highest. This may mean that this polyphenol is not the most significant factor in red wine. Yet there was no harm done, either, so that lovers of an after-dinner glass of red wine and a piece of dark chocolate can still enjoy their dessert with a clear conscience.
In short, all available evidence does not point to an effective cost-benefit ratio with respect to resveratrol supplementation, and there is a striking lack of human trial-based evidence of health benefits. This should lead to caution in taking large doses of resveratrol, especially when the aims, such as anti-carcinogenesis and lowered risk of coronary heart disease may be achieved in other more proven ways.