Spermidine
Spermidine is a small molecule your cells make and use, also found in foods such as wheat germ, mature cheese, mushrooms and fermented soy, and it is sold as a supplement said to switch on autophagy, the cell's recycling system. In animals, blocking it blunts fasting's recycling boost and cancels its life-extending effect. In people the case rests on one observational study, and the trial designed to test it came back null.
Don't take spermidine supplements expecting an anti-aging effect: the one long trial found no benefit, and a high oral dose did not even raise blood spermidine. Spermidine-rich foods are fine as part of a normal diet, but no form of spermidine has been shown to switch on autophagy in people.
What it is
Spermidine is a polyamine, one of a family of small molecules that cells need to grow and function. You get it from food, and your body makes its own: fasting raises it, which has been measured in yeast, flies, mice and human volunteers.[1] It is sold as a caloric-restriction mimetic, a compound meant to reproduce the cellular effects of eating less without eating less. The recycling system it is supposed to boost is explained on Disabled macroautophagy, and the wider family of anti-aging compounds is compared on Geroprotectors.
Why researchers got interested: animals and cells
The strongest evidence is from model organisms. Blocking spermidine production blunted fasting-triggered autophagy in yeast, worms and human cells, and cancelled fasting's lifespan benefit in animals. Spermidine works through a chemical tag on a protein called eIF5A, which boosts production of TFEB (transcription factor EB), the master switch for the cell's autophagy and digestion genes. Whether this chain matters for autophagy in people is not yet shown.[2]
There is also an immune thread. In aged mice, autophagy in T cells (immune cells that include the ones that remember past infections) is already low, and spermidine revived their T-cell responses.[3] In people the evidence is correlational and from the lab dish: in older vaccine recipients, T cells with less autophagy responded more weakly, and T cells from old donors regained autophagy and function when given spermidine in the lab.[4]
The observational case: one cohort
In one cohort of 829 adults aged 45 to 84 in northern Italy, people in the top third of spermidine intake had about 39% lower death rates from any cause than those in the bottom third. The link weakened once overall diet quality was accounted for.[5] That is the best epidemiological case for spermidine, and it is observational: people who eat more of these foods may differ from those who don't in many other ways.
The trial: null
The trial the field wanted came back null. In 100 adults aged 60 to 90 with subjective cognitive decline (people who feel their memory slipping before tests show it), 12 months of a spermidine-rich wheat-germ extract, about 0.9 mg of spermidine a day, improved neither memory nor the biomarkers compared with placebo. The authors themselves flag the low dose. Several of them, like several authors of the key animal work, hold equity in or advise the company that makes the trial's supplement.[6]
Higher doses may not arrive as spermidine. In 12 healthy volunteers, 15 mg a day by mouth for 5 days raised blood spermine, which the body makes from spermidine, but not spermidine itself.[7]
A 2026 pilot in 40 adults over 65 found that 6 mg a day for 13 weeks raised autophagy-gene activity in B cells (a type of immune cell), and improved vaccine responses only in people who had responded poorly before. It is small and unconfirmed, and its authors consult for spermidine sellers.[8]
What to do
- Don't buy it for autophagy or longevity. The one long trial was null, and the positive signal is a small pilot in a subgroup.
- Eat the foods if you like them, as part of a normal diet, without expecting a measurable effect.
- For the recycling system itself, exercise has the best human data. See Disabled macroautophagy.
Further reading
- Schwarz C, et al. Effects of Spermidine Supplementation on Cognition and Biomarkers in Older Adults With Subjective Cognitive Decline: A Randomized Clinical Trial. JAMA Netw Open 2022 — the SmartAge trial.[9]
- Kiechl S, et al. Higher spermidine intake is linked to lower mortality: a prospective population-based study. Am J Clin Nutr 2018.[10]
- Senekowitsch S, et al. High-Dose Spermidine Supplementation Does Not Increase Spermidine Levels in Blood Plasma and Saliva of Healthy Adults: A Randomized Placebo-Controlled Pharmacokinetic and Metabolomic Study. Nutrients 2023.[11]
- Hofer SJ, et al. Spermidine is essential for fasting-mediated autophagy and longevity. Nat Cell Biol 2024.[12]
- Alsaleh G, et al. Spermidine Mitigates Immune Cell Senescence and Boosts Vaccine Responses in Healthy Older Adults-A Pilot Study. Aging Cell 2026.[13]