Fisetin

Fisetin is a flavonoid found in strawberries. It entered the longevity conversation in 2018, when Yousefzadeh and colleagues screened a panel of flavonoids for senolytic activity and identified fisetin as the most potent at killing senescent cells in culture. In the same paper, fisetin treatment reduced senescence markers in tissue from aged mice, and extended median lifespan in already-old wild-type mice by roughly 10% when treatment started late in life [1]. That is a real result: an intermittent dose, not lifelong administration, given to already-old animals, still moved a hard outcome.

The result that gets left out of most supplement marketing came five years later. The National Institute on Aging's Interventions Testing Program, ITP, is the field's gold standard for lifespan claims: it tests a compound across three independent lab sites simultaneously, using genetically diverse mice, specifically to catch results that don't replicate outside a single lab's hands. When ITP tested fisetin, it found no lifespan extension in mice [2]. This is a direct, methodologically rigorous contradiction of part of the original 2018 excitement, and it has not been widely publicized outside specialist aging-research circles.

The two results are not strictly incompatible; they tested different things. Yousefzadeh's paper measured senescent cell burden and healthspan markers plus one lifespan cohort at a single site. ITP measured lifespan alone, across three sites, under its standardized protocol. But the gap between a well-cited 10% lifespan claim and a null result from the field's most rigorous replication test is exactly the kind of thing a supplement seller will not mention and a careful reader needs to know.

Human evidence for fisetin as a senolytic is sparser than for dasatinib plus quercetin. In a small Mayo Clinic pilot in older adults, a fisetin-taking subgroup showed significant drops in SASP factors MMP-3 and TGF-β1 (p<0.05) compared with baseline, alongside a reduction in senescent peripheral blood mononuclear cells (p=0.0039), though T-cell senescence burden was unchanged [3]. That is real biomarker movement in humans, but it is a small, mostly single-arm pilot, not a large randomized trial with a hard clinical outcome.

Fisetin's use in Bryan Johnson's Blueprint protocol is documented by third-party breakdowns at roughly 200 mg/day, generally taken as part of a broader senolytic rotation; this is a self-report, not evidence, and predates the 2023 ITP null result becoming widely known. Whether Johnson's protocol has been revised in light of that finding is not confirmed from an official Blueprint source at time of writing.

What critics say: the Fight Aging community, generally sympathetic to senolytic research, described the ITP null result as "puzzling" precisely because it contradicts multiple positive senescent-cell-clearance findings, and called for more work reconciling why a compound that clears senescent cells in tissue does not extend lifespan in a rigorous multi-site trial [2]. That is the right question, and it remains open.

The honest takeaway: fisetin clears senescent cells in mice and in culture. It has not been shown to extend mouse lifespan under the field's most rigorous replication protocol, and no large human trial has tested it alone against a hard outcome.

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