Spermidine is a polyamine your cells make and your food supplies, and it triggers autophagy, the process by which cells recycle their own damaged parts. Wheat germ, soya, mature cheese and mushrooms are the richest sources. People who eat more of it live longer in cohort studies. Randomised trials have been far less impressive.
Spermidine arrived in the longevity conversation with unusually good credentials. A molecule your own body makes, present in ordinary food, that extends the life of mice and tracks with lower mortality in a 20-year population study. No wonder the supplement market moved quickly.
The trials that followed have been quieter, and almost nothing written for a UK audience mentions them. This article covers both halves: what the animal and population evidence shows, what the randomised studies actually measured, and which foods carry enough spermidine to matter.
What is spermidine, and is it made of sperm?
No, though the name is not an accident. Antonie van Leeuwenhoek described crystals in human semen in 1678, and the polyamines eventually isolated from that source were named after it. Spermidine turns up in every living cell, from bacteria to oak trees, and the molecule in a bowl of soya is chemically identical to the one in your liver.
Structurally it is a small chain with three nitrogen atoms, molar mass 145 g/mol, positively charged at body pH. That charge is the point: spermidine binds to DNA, RNA and membrane surfaces, stabilising them. Cells cannot divide without polyamines at all.
You obtain it three ways. Your cells synthesise it from the amino acid ornithine, itself downstream of arginine, one of the amino acids your body makes except when illness outruns it; your gut bacteria produce it; and your diet delivers it. Tissue concentrations fall with age in most organs, which is the observation the whole field is built on.
What does spermidine do for the body?
The headline mechanism is autophagy. Cells continuously dismantle worn proteins and damaged mitochondria and reuse the parts, and that housekeeping slows down with age. Spermidine switches it on, chiefly by inhibiting the enzymes that acetylate certain proteins, which releases the brake on the autophagy programme.
There is a second job that gets far less attention. Spermidine is the only substrate for hypusination, a chemical modification made to a single protein called eIF5A, which cells need in order to translate a subset of messenger RNAs. Without spermidine, that modification cannot happen at all. It is not a nice-to-have.
In heart tissue, autophagy and mitophagy are how ageing cardiomyocytes stay functional. Reduced background inflammation shows up alongside those effects in animal work, which is why the molecule keeps appearing next to everyday anti-inflammatory approaches in longevity writing, though the two are separate questions with separate evidence.
Where your gut bacteria come in
A large share of the spermidine in your body never came from a plate or from your own cells. It came from the microbes in your colon, which synthesise polyamines as part of their ordinary metabolism and release them where the gut lining can absorb them.
That matters for two reasons. It means fibre, which feeds those bacteria, is an indirect route to spermidine as well as a direct one, since wholegrains and pulses carry both. And it means individual polyamine levels vary with the microbiome, which is one plausible explanation for why a fixed capsule dose behaves so inconsistently between people.
The caloric restriction mimetic idea
Madeo and colleagues frame spermidine as a caloric restriction mimetic: a compound that switches on the same cellular programme as eating less, without eating less. Their 2018 review in Science gathers the evidence across cancer, metabolic disease, cardiovascular disease and neurodegeneration, and the pattern is the same in each. Strong preclinical data, supportive epidemiology, thin clinical evidence.
What the animal work showed
The strongest single paper remains Eisenberg and colleagues in Nature Medicine. Oral spermidine extended the lifespan of mice and protected their hearts, reducing cardiac hypertrophy and preserving diastolic function in old animals. Cardiac autophagy, mitophagy and mitochondrial respiration all rose.
One detail in that paper matters more than the lifespan number. The cardioprotection disappeared in mice engineered to lack Atg5, a protein autophagy cannot run without. That is a mechanistic proof rather than a correlation: remove the pathway and the benefit goes with it.
In salt-sensitive rats fed a high-salt diet, a model of hypertensive heart failure, spermidine lowered blood pressure and delayed the slide into failure. Consistent, mechanistically coherent, and still a rodent.
The population data, and the number everyone quotes
Human evidence begins with the Bruneck study in northern Italy. Kiechl and colleagues followed 829 participants aged 45 to 84 years, with repeated dietitian-administered food questionnaires across 20 years. In that time 341 deaths occurred.
Deaths per 1 000 person-years fell from 40.5 in the lowest third of spermidine intake to 15.1 in the highest. Adjusted for age, sex, calories, lifestyle and other dietary factors, each standard deviation of extra spermidine intake carried a hazard ratio of 0.76. The finding held in a second Austrian cohort.
The mortality gap between the top and bottom third of spermidine intake was similar to the gap associated with being 5.7 years younger, across 829 people followed for 20 years.
Kiechl et al., American Journal of Clinical Nutrition, 2018. DOI: 10.1093/ajcn/nqy102
That comparison is the sentence every supplement page repeats, and it is worth stating what it is. An observational cohort, adjusted carefully, but still describing people who chose to eat differently. High-spermidine diets are wholegrain, legume-heavy, vegetable-heavy diets. Untangling the polyamine from the pattern it arrives in is exactly what a cohort study cannot do.
What happened in the randomised trials
Three human trials have tested spermidine supplements properly, and none of them appears on the UK pages that sell it.
Wirth and colleagues ran the pilot in 2018: 30 older adults with subjective cognitive decline, 3 months, a spermidine-rich wheat germ extract against placebo. Memory performance improved with a medium to large effect size. Encouraging, and far too small to settle anything.
The same group then built the trial that would settle it. SmartAge randomised 100 participants aged 60 to 90 years to 12 months of a wheat germ extract delivering 0.9 mg of spermidine a day, or to placebo. Retention was 89 per cent. The primary outcome was memory, measured by a mnemonic discrimination task.
Nothing moved. The between-group difference was 0.03 with a confidence interval running through zero, and the secondary outcomes and biomarkers behaved the same way. Exploratory analyses hinted at effects on verbal memory and inflammation, and the authors were careful to label them as hypotheses for a higher dose.
Then there is the dose question, answered in 2024. Keohane and colleagues gave 37 healthy men aged 50 to 70 years 40 mg a day of high-purity spermidine, more than forty times the SmartAge dose, for 28 days. It was safe and well tolerated, with no product-related adverse events and no change in blood chemistry. It also barely shifted serum and urine polyamine concentrations.
MICE AND RATS
Lifespan extended, hearts protected, effect abolished without Atg5. Consistent and mechanistically clean.
COHORT STUDIES
829 people, 20 years, hazard ratio 0.76 per standard deviation of intake. Diet pattern and molecule cannot be separated.
RANDOMISED TRIALS
100 participants, 12 months, no change in memory or biomarkers. 40 mg a day barely moves circulating polyamines.
The dose is the obvious objection to SmartAge, and it is a fair one. A wheat germ extract at 0.9 mg a day sits below what a decent lunch supplies, so the trial arguably tested whether a small top-up on an already adequate intake changes memory. The authors say as much, and call for a higher-dose study. The 2024 work then showed that even 40 mg a day leaves circulating polyamines close to where they started, which complicates the plan.
Read together, those results suggest that the body regulates its polyamine pool tightly, and that swallowing more spermidine does not straightforwardly raise it. That is a plausible reason the cohort signal has not reproduced in a trial, and it is the most interesting open question in the field.
Which foods are high in spermidine?
This is where the evidence is least contested, because the cohort participants were not taking capsules. They were eating.
| Food | Approximate spermidine per 100 g | Realistic in a UK diet |
|---|---|---|
| Wheat germ | 20 to 25 mg | The densest source by a wide margin, and a spoonful goes into porridge or yoghurt |
| Natto and other fermented soya | 5 to 10 mg | Fermentation adds bacterial polyamines on top of the bean |
| Dried soya beans | 2 to 8 mg | Tofu and edamame count |
| Mature cheddar and other aged cheese | 2 to 20 mg | Rises with age of the cheese, which is why figures vary so widely |
| Mushrooms | 4 to 9 mg | Easy, cheap and underrated |
| Peas, broccoli, cauliflower | 1 to 5 mg | Low per 100 g, high per portion |
Typical Western intake lands somewhere around 10 to 15 mg a day, and the Bruneck participants in the top third were not eating exotically. They were eating more wholegrain, more pulses, more vegetables and more mature cheese than the bottom third.
Two practical notes. Spermidine survives ordinary cooking, so there is no need to eat anything raw for it. And wheat germ oxidises quickly once opened, so a smaller bag kept in the fridge beats a large one in the cupboard.
Supplements in the UK, and what a label may say
Almost every spermidine product sold in Britain is a wheat germ extract standardised to a stated milligram figure, not pure spermidine. That is worth knowing, because the 2024 safety trial had to describe high-purity spermidine as novel precisely because it had not been available for human use.
Doses on UK shelves cluster between 1 and 10 mg a day. SmartAge used 0.9 mg and found nothing over a year. The trial that used 40 mg was a 28-day safety study, not an efficacy study, so no trial has yet shown a benefit at any dose you can currently buy.
On claims, the position is the same as for most longevity ingredients. Spermidine carries no entry on the GB Nutrition and Health Claims Register, so a product sold in Great Britain may not lawfully claim that it slows ageing, promotes longevity or triggers autophagy in you. The NAD+ precursors sit in the same position, with not one authorised claim between them. Where you see such wording on a UK site, it is outside what the register permits, whatever the mouse data says.
None of this makes spermidine a bad idea. It makes the food route the defensible one, and it means a capsule should be judged against a bag of wheat germ costing a couple of pounds rather than against nothing.
Side effects, and who should take care
The safety record in trials is good. Across 12 months in SmartAge, adverse events were balanced between the spermidine and placebo groups. Across 28 days at 40 mg a day, no product-related adverse events were reported and blood chemistry, lipids and haematology were unchanged.
Three groups should still think before supplementing. Wheat germ extracts are wheat, so anyone with coeliac disease or a wheat allergy needs to check the product rather than assume. Polyamines support cell proliferation, and polyamine-restricted diets have been studied in oncology, so anyone with a current cancer diagnosis should raise it with their oncology team rather than decide alone. And there is no safety data in pregnancy.
For everyone else, the sensible framing is that this is a nutrient, not a drug. If ageing joints or stiffness are what brought you to a longevity page in the first place, the evidence for approaches aimed directly at joint comfort is a separate conversation with separate trials behind it.
What deserves confidence here is the food pattern. What deserves patience is the molecule. A higher-dose trial is the obvious next step, and until it reports, the honest summary is that spermidine is one of the better bets in longevity research and not yet a demonstrated one.
Frequently asked questions
What foods are high in spermidine?
Wheat germ leads by a wide margin at roughly 20 to 25 mg per 100 g. Fermented soya such as natto, mature cheese, mushrooms, dried soya beans, peas and broccoli follow. Spermidine survives normal cooking, so nothing needs to be eaten raw to get it.
What does spermidine do for the body?
It triggers autophagy, the recycling process cells use to clear damaged proteins and mitochondria, and it is the only substrate for hypusination of the protein eIF5A, which cells need to translate certain messenger RNAs. In mice it extended lifespan and protected the heart.
Is spermidine made of sperm?
No. The name comes from history: Antonie van Leeuwenhoek described crystals in human semen in 1678, and the polyamines later isolated from that source took the name. Spermidine occurs in every living cell, and supplements are made from wheat germ.
Does spermidine actually work in humans?
The cohort evidence is encouraging: 829 people followed for 20 years showed a hazard ratio of 0.76 per standard deviation of intake. The randomised evidence is not. Over 12 months in 100 older adults, 0.9 mg a day produced no change in memory or biomarkers against placebo.
How much spermidine should I take?
No trial supports a dose, which is the honest answer. UK products deliver roughly 1 to 10 mg a day, the trial that found nothing used 0.9 mg, and the 40 mg study ran for 28 days as a safety check rather than a test of benefit. Typical dietary intake is around 10 to 15 mg a day.
Does spermidine have side effects?
Adverse events were balanced against placebo over 12 months, and 40 mg a day for 28 days changed no blood chemistry or haematology. Wheat germ extracts contain wheat, so check the label if you are coeliac. There is no safety data in pregnancy.
Which is better, spermidine or NMN?
Neither has a randomised trial showing a hard clinical benefit in humans, so better is not yet answerable. Spermidine has the stronger population data and a food route that costs almost nothing. Neither carries an authorised health claim on the GB register.
Sources
- Madeo F., Eisenberg T., Pietrocola F., Kroemer G. Spermidine in health and disease. Science, 2018. DOI: 10.1126/science.aan2788
- Eisenberg T., Abdellatif M., Schroeder S., et al. Cardioprotection and lifespan extension by the natural polyamine spermidine. Nature Medicine, 2016. DOI: 10.1038/nm.4222
- Kiechl S., Pechlaner R., Willeit P., et al. Higher spermidine intake is linked to lower mortality: a prospective population-based study. The American Journal of Clinical Nutrition, 2018. DOI: 10.1093/ajcn/nqy102
- Wirth M., Benson G., Schwarz C., et al. The effect of spermidine on memory performance in older adults at risk for dementia: a randomized controlled trial. Cortex, 2018. DOI: 10.1016/j.cortex.2018.09.014
- Schwarz C., Benson G.S., Horn N., et al. Effects of spermidine supplementation on cognition and biomarkers in older adults with subjective cognitive decline: a randomized clinical trial. JAMA Network Open, 2022. DOI: 10.1001/jamanetworkopen.2022.13875
- Keohane P., Everett S., Pereira K., et al. Supplementation of spermidine at 40 mg/day has minimal effects on circulating polyamines: an exploratory double-blind randomized controlled trial in older men. Nutrition Research, 2024. DOI: 10.1016/j.nutres.2024.09.012
This article is general information, not medical advice. Speak to your GP or a pharmacist before starting a supplement, particularly if you are pregnant, have coeliac disease, or are under the care of an oncology team.
