Neither, on current human evidence. Spermidine's most rigorous trial — twelve months at the 0.9 mg/day dose supplements actually use — missed its primary memory endpoint. Fisetin's headline mouse lifespan result was not replicated by the NIA's testing program in 2024. Both occur in food; for spermidine, the mortality signal comes from dietary intake in cohorts, not from capsules.
| Compared on | Spermidine | Fisetin |
|---|---|---|
| Evidence grade | Moderate evidence | Emerging evidence |
| What it is | Spermidine is a naturally occurring polyamine present in all human cells and obtained from the diet, with wheat germ, soybeans, aged cheese, mushrooms and other fermented or plant foods among the richest sources. | Fisetin is a naturally occurring flavonol (a plant polyphenol) found in strawberries, apples, persimmons, onions, and other fruits and vegetables. |
| Best human evidence | “exploratory analyses indicated possible beneficial effects on verbal memory and inflammation” JAMA Netw Open 2022 · PMID 35616942 | “The NIA Interventions Testing Program's rigorous multi-site mouse lifespan study found fisetin did not significantly extend lifespan at the dose and schedule tested - a key non-replication…” GeroScience 2024 · PMID 38041783 |
| Dose / protocol studied | ~0.9–3.3 mg/day (wheat-germ extract) | 100 mg/day for 7 weeks in the trial that lowered IL-8 and hs-CRP. No senolytic schedule is established for healthy adults. |
| Typical listed price | $44.95 | $38.56 |
| Who it suits | Someone who wants the autophagy mechanism with the strongest preclinical case and the largest supporting cohort data, and who accepts the trial result was null. | Someone tracking the senolytic field who wants exposure to the most potent screened flavonol and understands the trials are still running. |
| Who should skip it | Anyone expecting a cognitive benefit at supplement doses — the 12-month randomized trial at 0.9 mg/day found none on its primary outcome. | Anyone treating it as an established anti-aging intervention. Reviewers caution senolytics should not yet be used outside clinical trials. |
| Key caveat | The preclinical case is unusually strong and several large prospective cohorts link higher dietary spermidine intake to lower mortality — but that is observational and confounded by diet quality. The most rigorous human trial to date (12-month SmartAge) found no cognitive or biomarker benefit at the 0.9 mg/day dose used in supplements, and oral bioavailability is unsettled. | Nearly all senolytic evidence is preclinical, and the 2018 mouse lifespan finding was not replicated by the NIA Interventions Testing Program in 2024. Small human RCTs show anti-inflammatory effects (for example 100 mg/day for 7 weeks in cancer patients), but no published trial has shown senescent-cell clearance or aging benefits in healthy people. Anti-aging use remains speculative pending larger trials. |
Spermidine lists at about 1.2× the price of Fisetin. Prices are the typical listed prices in our catalog, not live Amazon prices, and a true cost-per-studied-dose is not shown because our catalog does not record servings per container — we would have to guess, so we don't.
Autophagy and senescent-cell clearance are different hallmarks of aging. Both compounds have a strong preclinical story and a thin human one — but the thinness is different in each case.
Spermidine. Prospective cohorts — Bruneck, NHANES, UK Biobank and Takayama — link higher dietary spermidine intake to lower all-cause and cardiovascular mortality; in Bruneck each standard-deviation increase tracked with about a 26% lower hazard of death over 20 years. That is dietary intake, observational, and confounded by overall diet quality.
Fisetin, in the narrow sense. Fisetin 100 mg/day for 7 weeks significantly lowered plasma IL-8 and hs-CRP versus placebo in a double-blind randomized trial — but that was 37 colorectal-cancer patients on chemotherapy, not healthy adults.
Neither. The 12-month SmartAge randomized trial of spermidine at the commercial dose found no benefit on its primary memory outcome or biomarkers; exploratory analyses hinted at verbal memory and inflammation effects, which is a hypothesis, not a result.
You may already be at the studied dose. A normal diet supplies roughly 10–15 mg of spermidine a day, which exceeds the 0.9–1.2 mg/day doses used in the cognition trials. Wheat germ alone holds about 24–35 mg per 100 g.
Spermidine's rigorous trial was null and its bioavailability is unsettled — a pharmacokinetic study found oral spermidine is largely converted to spermine. Fisetin's flagship lifespan result did not survive independent replication.
Both are cheap in food. Wheat germ is the single richest everyday spermidine source, alongside natto, aged cheese and mushrooms; strawberries carry fisetin in the highest abundance among common foods. If the mechanism matters to you, that is where the cohort evidence actually lives.
Cited: JAMA Netw Open 2022 · PMID 35616942 · GeroScience 2024 · PMID 38041783
Each quote below is taken verbatim from the cited paper. Null and negative results are included on purpose — they are the reason a grade means anything.
“exploratory analyses indicated possible beneficial effects on verbal memory and inflammation”
“The difference in mortality risk between the highest and lowest spermidine intake was statistically comparable to being 5.7 years younger.”
“Administration of spermidine, a natural polyamine, markedly extended the lifespan of yeast, flies and worms, and human immune cells, by triggering autophagy.”
“The NIA Interventions Testing Program's rigorous multi-site mouse lifespan study found fisetin did not significantly extend lifespan at the dose and schedule tested - a key non-replication of the 2018 lifespan finding.”
“In a double-blind RCT of 37 colorectal cancer patients on chemotherapy, fisetin 100 mg/day for 7 weeks significantly lowered plasma IL-8 and hs-CRP versus placebo.”
“The 2017 mechanistic study that identified fisetin as a senolytic, showing it selectively induces apoptosis in senescent murine and human cells.”
Links go to an Amazon search for the product name, not to a specific listing, so you can compare sellers, price and third-party testing yourself.
Neither has human evidence for a longevity outcome. Spermidine has the larger observational base — several prospective cohorts link higher dietary intake to lower mortality — but its best randomized trial was null on its primary endpoint.
Roughly 24–35 mg per 100 g, or about 2–2.5 mg per tablespoon. A normal diet supplies around 10–15 mg/day, which is above the 0.9–1.2 mg/day used in the human cognition trials.
It missed its primary endpoint. Twelve months of spermidine at 0.9 mg/day in older adults with subjective cognitive decline produced no benefit on the primary memory outcome or biomarkers; exploratory analyses suggested possible effects on verbal memory and inflammation.
Reviewers caution that senolytics should not yet be used outside clinical trials. Fisetin at the doses in supplements is generally well tolerated, but tolerability is not efficacy, and the trials that would establish efficacy in healthy people are still running.
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