Spermidine

What spermidine is

Spermidine belongs to the polyamines, small molecules involved in cell division and protein synthesis in every cell. Your body makes it itself, so do your gut bacteria, and you take it in through food. The starting point of longevity research: the concentration in tissue declines over the course of life. This observation stood at the beginning when a research group in Graz showed in 2009 that supplemented spermidine extends the life of yeast, flies and worms.

Spermidine is almost always sold as wheat germ extract, authorized in the EU with a fixed specification. There is also high-purity spermidine trihydrochloride, used mainly in research, and extracts from rice germ.

The autophagy narrative and where it arrives in humans

Autophagy is the process by which cells break down and recycle damaged components. Fasting switches it on, and because spermidine does the same in the laboratory, advertising likes to call it “fasting in pill form”. The evidence from animal models is strong: in 2009, autophagy was demonstrably necessary for spermidine to extend lifespan, and in the Nature Medicine paper of 2016 the heart protection in mice failed to appear when the heart muscle cells were deprived of the autophagy protein Atg5. This is not a correlational finding, but a mechanism that can be switched off.

In humans, it gets thin. Only in 2026 did a group in Oxford measure autophagic flux under spermidine directly: double-blind, placebo-controlled, 40 participants aged 65 and over, 6 milligrams daily over 13 weeks. After 2 weeks, flux in B cells was increased compared with placebo, in T cells it was not. The primary endpoint was safety, and the authors themselves call everything immunological exploratory. A single-blind pilot study with 12 participants found increases under rice germ extract in the markers beclin-1 of 7.3 percent and ULK-1 of 13.4 percent compared with baseline. That is the complete stock of autophagy measurements in humans.

What reaches the blood from a capsule

This is the most uncomfortable point. A triple-blind crossover study gave 12 healthy volunteers 15 milligrams of spermidine daily over 5 days. Spermidine in plasma did not rise; what rose was spermine, the conversion product. The authors consider amounts below 15 milligrams daily ineffective in the short term. A second study went higher: 37 men between 50 and 70 years of age received 40 milligrams daily over 7 and over 28 days, without any substantial change in polyamine levels in serum and urine. The studies with positive signals used 0.9 to 6 milligrams daily.

Spermidine in food

The cohort data on which the narrative rests come from food, not from capsules. A Spanish analysis found the highest polyamine content of all in wheat germ, at 440.6 milligrams per kilogram. Over 90 milligrams per kilogram were also found in mushrooms, green peppers, peas, citrus fruits and tempeh, with spermidine as the main polyamine. In hard and blue cheeses, by contrast, putrescine dominates, not spermidine. Cooking and grilling reduced the content by up to 64 percent.

What the studies show

SmartAge – the decisive study on wheat germ extract

Randomized, double-blind, placebo-controlled phase 2b study in Germany, January 2017 to May 2020. 100 people between 60 and 90 years of age with subjective cognitive decline received wheat germ extract with 0.9 milligrams of spermidine daily (51 people) or placebo (49 people) for 12 months; 89 completed the study. The primary endpoint was mnemonic discrimination performance. Result: no difference, group difference −0.03 with a confidence interval of −0.11 to 0.05 and p = 0.47. All secondary endpoints also remained unchanged. Exploratory analyses hinted at effects on inflammation markers and verbal memory; the authors themselves say this needs validation.

The pilot study before it

The same research group published a phase IIa pilot study in 2018 with 30 participants between 60 and 80 years of age over 3 months at 1.2 milligrams daily, evaluated via effect sizes rather than significance tests. Memory performance was moderately better than with placebo, with a Cohen's d of 0.77, but the confidence interval ranged from 0 to 1.53 and included zero. This study is the starting point of most spermidine advertising copy; SmartAge was the attempt to confirm it.

Bruneck and mortality

Prospective cohort study with 829 participants, 2,540 dietary assessments and 341 deaths between 1995 and 2015. The adjusted hazard ratio for all-cause mortality was 0.76 per standard deviation of higher intake, and 0.71 in the validation cohort SAPHIR. The authors put the gap between the top and bottom thirds as large as the difference to an age 5.7 years younger. What was measured was spermidine from food, not from supplements – people who eat a lot of it usually also eat differently in other respects.

The first randomized study with a clinical endpoint

It comes from oncology, not from longevity research. 58 patients facing head and neck radiotherapy received, double-blind, 1 milligram of spermidine daily or placebo, 29 per group. After 3 months, 48.28 percent of the spermidine group had dry mouth compared with 79.31 percent under placebo, p = 0.0391. The authors themselves call it a proof of concept. It shows that spermidine can move a clinical endpoint in humans – in a special situation.

Where the data stop

The chain from yeast to humans has a gap, and it sits exactly where the advertising is loudest. Autophagy induction has been shown causally in model organisms, but in humans it has been measured in only one pilot study with 40 participants, there in only one cell population and at only one time point. That a capsule does the same in you as fasting is to this day not a measured fact. Then there is the pharmacokinetics: if 15 and even 40 milligrams daily do not raise the spermidine level in the blood, it remains unclear how smaller amounts are supposed to reach a cell in the heart muscle.

Hard endpoints in humans are completely missing. No completed randomized study shows that spermidine prevents heart attacks, dementia or deaths. A randomized study in heart patients was completed in June 2026; results are not yet available: POLYCAD in Denmark, 187 patients aged 65 and over with coronary heart disease, 24 milligrams daily over 12 months. It too measures no hard endpoints, but heart muscle mass, muscle mass, CRP and oxygen uptake. The hair data also carry less weight than product pages suggest: the only randomized study on this names neither the composition of the tablet nor the amount of spermidine, and it was funded by the manufacturer.

Status, approval and legal

Wheat germ extract from Triticum aestivum with a high spermidine content is a novel food in the EU under Regulation (EU) 2015/2283 and is on the Union list. It was added following a notification by the Austrian company TLL The Longevity Labs GmbH dated December 6, 2017; the Commission adjusted the specifications with Implementing Regulation (EU) 2020/443 of March 25, 2020, prescribing 0.8 to 2.4 milligrams of spermidine per gram of extract. The authorized maximum amount is 6 milligrams of spermidine per day, for adults excluding pregnant and breastfeeding women. Health claims for spermidine are not authorized in the EU – promises made on product pages are therefore, as a rule, unlawful. Spermidine is not on the WADA Prohibited List.

Safety

At the amounts on the market, spermidine is well tolerated, and this has been tested under controlled conditions. Over 12 months, adverse events in SmartAge were balanced between 51 active and 49 placebo participants, and even 40 milligrams daily over 28 days caused no product-related events in 37 men. What is missing are data beyond 12 months: as a food, spermidine is not subject to any pharmacovigilance. There are clear limits nonetheless. The EU authorization excludes pregnant and breastfeeding women. The Verbraucherzentrale (German consumer advice centre) advises people with cancer and people on immunosuppressive medication to take spermidine supplements only after consulting a physician, because high-dose spermidine can promote growth in certain tumors. The raw material is wheat germ – the Oxford pilot study excluded people with gluten intolerance.

Sources

• Schwarz et al., JAMA Network Open 2022 (SmartAge)
• Wirth et al., Cortex 2018 (pilot study)
• Kiechl et al., Am J Clin Nutr 2018 (Bruneck)
• Eisenberg et al., Nature Medicine 2016
• Eisenberg et al., Nature Cell Biology 2009
• Alsaleh et al., Aging Cell 2026 (autophagy and vaccine response)
• Senekowitsch et al., Nutrients 2023 (pharmacokinetics)
• Keohane et al., Nutrition Research 2024 (40 mg per day)
• Muñoz-Esparza et al., Foods 2021 (polyamines in foods)
• Commission Implementing Regulation (EU) 2020/443