GlaxoSmithKline could put SRT501, its resveratrol formulation, on the market right away, selling it as a natural compound and nutritional pharmaceutical that does not require approval by the F.D.A. “We haven’t made any decisions, but that clearly is an option,” Dr. Vallance said.

If GlaxoSmithKline decides instead to seek F.D.A. approval, it will need to prove that resveratrol is safe in the large doses required for efficacy. Resveratrol seems to exert many influences on the body, some of which are not exerted through sirtuin. “None of us should be naïve enough to think resveratrol won’t have multiple effects, including some you don’t want,” Dr. Vallance said.

GlaxoSmithKline’s purchase of Sirtris has pushed the optimism of sirtuin researchers and others to new heights. “We are all holding our breath,” said Dr. Huber Warner, editor of the Journals of Gerontology. But the success of the drugs is far from assured.

Most potential drugs fail to make it past clinical trials, and the same may prove true for Sirtris’s candidates. The sirtuin-activating chemicals the company has designed could turn out to be toxic. Another uncertainty is that the underlying science is still in flux and debate rages among academic researchers over many details of how caloric restriction works.

Some biologists think that sirtuin is not the only mediator of the famine reflex, and that resveratrol may not work through sirtuin at all in exerting its beneficial effects on mice. “There are data both for and against that hypothesis, though that doesn’t dissuade one from pursuing it as a potential benefit,” said Dr. Thomas Rando, who studies aging in stem cells at Stanford University.

In initial tests in mice, resveratrol has doubled muscular endurance, lowered the bad form of cholesterol, protected against various bad effects of a high-fat diet and suppressed colon cancer. New reports are confirming some of these benefits, but others are ambiguous or puzzling.

According to a study published on July 3 in the journal Cell Metabolism by Dr. Sinclair and Dr. Rafael de Cabo of the National Institute on Aging, resveratrol given to aging mice reduced their cataracts, strengthened their bones, improved coordination and enhanced their health in several other ways. Yet despite their better health, the mice lived no longer than usual.