Fisetin

Fisetin is a flavonol — the same chemical family as quercetin — concentrated in strawberries (by far the richest food source), with smaller amounts in apples, persimmons, grapes and onions. Diet delivers only milligrams a day.

Its headline appeal is as a senolytic: a compound that selectively nudges senescent cells — damaged cells that stop dividing but linger and pump out inflammatory signals (“inflammaging”) — toward self-destruction. Clearing that burden is a leading anti-ageing hypothesis.

Strong — in mice

The landmark study (Yousefzadeh et al., EBioMedicine 2018) screened flavonoids and found fisetin the most potent senolytic. In aged mice it reduced senescent-cell markers across multiple tissues, improved health measures, and extended both median and maximum lifespan — notably even when treatment began late in life.¹ That combination is what put fisetin on the longevity map.

Not yet shown — in humans

There is currently no published randomised trial demonstrating a senolytic or anti-ageing benefit of fisetin in people. Several Phase 2, placebo-controlled trials are underway — in frailty and inflammation in older adults, in chemotherapy-related functional decline in breast-cancer survivors, and in bone health.² Until those report, human claims are hypothesis, not established fact. Treat the confident marketing with caution.

Supplements are typically sold at 100–500 mg/day, but that daily model is borrowed from ordinary antioxidants. The trial protocol is different: a short, intermittent “hit-and-run” course of about 20 mg/kg per day for 2–3 consecutive days, repeated occasionally (e.g. monthly) — the idea being to clear senescent cells in a pulse rather than saturate the body continuously.

Absorption is poor (like quercetin), so it is usually taken with a fatty meal, and liposomal or phytosome forms are marketed to improve uptake. Honestly: the optimal human dose is unknown — all of this is experimental.

As a compound we already eat, fisetin looks well tolerated short-term, and the intermittent trial dosing has so far reported few problems. But long-term safety of high-dose supplements in humans is not established.

Like quercetin, it can affect drug-metabolising enzymes, so be cautious alongside medications; avoid in pregnancy and breastfeeding (no safety data). It is of interest to the longevity-curious — but the honest summary is that this is a promising experiment, not an established anti-ageing supplement.