Spermidine

Autophagy declines with age, and boosting it extends lifespan in yeast, flies, worms and mice — spermidine is one of the cleaner ways to trigger it. In animals it improves cardiac function and, in some models, lifespan, largely through this recycling pathway.³ That is a real mechanistic story, not marketing vapour, which is why serious researchers take it seriously. The caveat is the familiar one on this shelf: mechanism in a mouse is a hypothesis about humans, not a result in them.

The finding that made spermidine famous came from the Bruneck study, which tracked diet and mortality in an Italian town: people in the highest tier of dietary spermidine intake had notably lower all-cause mortality than those in the lowest, a gap the authors likened to being several years younger.¹ It is a genuinely eye-catching association — but it is an association. High-spermidine eaters also tend to eat more whole grains, legumes and vegetables and less processed food, so the polyamine may be a marker of an overall healthier diet rather than the active ingredient. Observational data can motivate a trial; they cannot substitute for one.

This is where expectations should come down to earth. The most rigorous human test so far gave a spermidine-rich wheat-germ supplement to older adults at risk of cognitive decline for a year and found no significant improvement in memory versus placebo — the supplement was safe and raised intake, but the hoped-for cognitive benefit did not materialise.² Smaller pilot studies had hinted at benefit; the larger, better-controlled trial did not confirm it. That does not close the book — cardiovascular and other endpoints are still being studied — but it means anyone selling spermidine as a proven brain or longevity aid is overstating a genuinely unsettled case.

Because the strongest evidence is dietary, the most defensible move is simply to eat more spermidine-rich foods — wheat germ, mushrooms, mature cheeses, soy and other legumes, whole grains — which brings the polyamine along with fibre and the rest of a good diet. If you want the supplement, the studied form is a wheat-germ extract standardised to a stated spermidine content, in the range of about 1–6 mg/day. It is well tolerated with no serious safety signals in the trials, though long-term data are limited; as with any of these, skip it in pregnancy for lack of data, and do not expect it to do the heavy lifting that diet and exercise do.