Resveratrol (3,5,4'-trihydroxy-trans-stilbene) is a stilbenoid, a type of natural phenol, and a phytoalexin produced naturally by several plants when under attack by pathogens such as bacteria or fungi.

The effects of resveratrol are currently a topic of numerous animal and human studies. Its effects on the lifespan of many model organisms remain controversial, with uncertain effects in fruit flies, nematode worms,and short-lived fish. In mouse and rat experiments, anti-cancer, anti-inflammatory, blood-sugar-lowering and other beneficial cardiovascular effects of resveratrol have been reported. These results have yet to be replicated in humans.

In the only positive human trial, extremely high doses (3–5 g) of resveratrol, in a proprietary formulation designed to enhance its bioavailability, significantly lowered blood sugar. This 28-day Phase 1b study was conducted privately in India by pharmaceutical company Sirtris, and was announced in an investors conference in early 2008. However, although it has been alluded to in review articles, the study itself has never been published in a peer-reviewed scientific publication. Despite mainstream press alleging resveratrol's anti-aging effects,there is no accepted data to form a scientific basis for the application of these claims to mammals (see Life-Extension section below). There are also a number of potential dangers posed by resveratrol.

Supplementation

As a result of extensive news coverage,sales of supplements greatly increased in 2006,despite cautions that benefits to humans are unproven.

Supplements vary in purity, and can contain anywhere from 50 percent to 99 percent resveratrol. Many brands consist of an unpurified extract of Japanese knotweed; these contain about 50 percent resveratrol by weight as well as emodin, which, while considered safe in moderate quantities, can have a laxative effect in high amounts.

Harvard University scientist Professor David Sinclair is often quoted in online ads. Sinclair, who has studied resveratrol extensively, has gone on record in Bloomberg Businessweek to say he never uttered many of the statements attributed to him on these sites.