In short
Resveratrol is a polyphenol compound produced by certain plants (notably grape skins, and therefore red wine) in response to stress or fungal infection, popularized as a longevity compound after early research suggested it activated sirtuins.
Resveratrol entered mainstream longevity interest after mouse studies from David Sinclair's lab and others reported lifespan or healthspan benefits, framed around the idea that it directly activated SIRT1. That specific mechanistic claim has since been substantially challenged: follow-up research found that the original in-vitro assay used a fluorescently tagged substrate, and resveratrol's apparent SIRT1 activation in that assay did not hold up with the natural, untagged substrate, casting doubt on direct SIRT1 activation as resveratrol's primary mechanism in vivo.
The mouse lifespan data itself is also more nuanced than often portrayed: the most cited benefit was seen in mice fed a high-calorie, high-fat diet, where resveratrol appeared to counteract some of the diet's negative metabolic effects, while standard-diet mice showed little to no lifespan extension — suggesting resveratrol's effect, if real, may be more about mitigating metabolic stress than a general pro-longevity mechanism.
Human randomized trials of resveratrol have generally shown modest or inconsistent effects on cardiometabolic markers, with poor oral bioavailability (resveratrol is rapidly metabolized and cleared) cited as one plausible reason clinical effects have been harder to demonstrate than the cell-culture data suggested. There is no human trial evidence that resveratrol extends lifespan or produces a clear, reproducible healthspan benefit at commercially available doses, and it should be treated as a compound with an actively contested primary mechanism rather than a settled sirtuin-activating longevity therapy.