What it's actually good for
Quercetin is one of the most abundant dietary flavonoids, found in onions, apples, berries, and capers. Unlike many compounds in the longevity space, quercetin has a reasonably substantial human evidence base for its anti-inflammatory and immune-supporting effects. Meta-analyses of randomized controlled trials show it reliably reduces C-reactive protein and other inflammatory markers, and there is decent evidence for modest blood pressure reduction and reduced upper respiratory infections in athletes and people under physical stress. Its more speculative role is as a senolytic — the dasatinib + quercetin combination has shown promise in pilot human studies for clearing senescent cells, but quercetin alone has not been established as an effective senolytic at typical supplement doses. The anti-inflammatory and immune evidence earns it a B grade, making it one of the better-supported flavonoid supplements, though bioavailability remains a practical challenge that affects real-world efficacy.