Wheat-stalk ladder with glowing yeast, worms and flies on its rungs, a mouse at its foot and a dashed gap line above
October 09, 2026

Spermidine: What the Science Actually Shows (Yeast to Humans)

By SciRouter Editorial Team · Last reviewed: 9 October 2026

Spermidine is a natural compound called a polyamine. It is the main polyamine in plant foods, and wheat germ, soybeans and mushrooms are rich sources[1–3]. In several lab studies, adding it extended lifespan in yeast, worms, flies and mice[4, 5]. In people, the evidence is diet associations and small trials, and the longest placebo-controlled trial missed its main memory goal[6, 7].

This guide climbs the evidence from yeast to people, marks where the lifespan evidence stops, and sums up doses, safety, food and supplement labels. For more depth, see our guides to foods high in spermidine, spermidine dosage in studies and spermidine side effects and safety, plus our page on whether spermidine can stand in for fasting.

How we researched this. On 8 October 2026 we searched PubMed through NCBI E-utilities and read open full text on Europe PMC and PubMed Central where we could. We also checked agency pages from the US FDA, the UK Food Standards Agency, Health Canada and EFSA. We put human trials and meta-analyses first, labelled every animal and cell study by species, and cited only sources we opened and checked against PubMed or Crossref. We note industry funding where authors disclosed it. This page cites 50 numbered sources plus one PubMed search. It is not medical advice.

What is spermidine?

Spermidine is a small molecule in the polyamine family, a group of compounds that cells need to grow[8]. You get it from food, your body makes it, and gut bacteria make polyamines too[1, 8, 9].

  • Where it is found. Spermidine is the main polyamine in plant foods, while its relative spermine is generally higher in animal foods[1].
  • How much people eat. Estimates of average intake compiled in a 2019 review ranged from about 4.8 mg a day in Turkey to about 15 mg a day in Spain[1].
  • No official target. There is no recommended daily intake for spermidine or other polyamines[1].
  • Ageing. Levels do not simply fall with age. A 2020 review described the age-related decline as complex, varying by tissue and cell type[10]. In a small Italian study of 78 people, adults aged 60 to 80 had the lowest blood spermidine of three age groups[11].

What does spermidine do in the body?

Cells use spermidine for growth, and in lab studies it switched on autophagy, the cell's recycling system[4, 8, 12]. In a 2009 study in yeast, worms and flies, its lifespan effect depended on that recycling[4].

In autophagy, the cell sends worn-out material to the lysosome, its digestion compartment, which breaks it down into parts and fuel the cell can reuse[13]. More is not always better: a 2008 review cautioned that autophagy may be harmful in some experimental disease models[14].

Lab studies traced spermidine's autophagy effect to two routes, through the enzyme EP300 and the protein eIF5A, in human cells and old mice, not people[12, 15]. In people, a placebo-controlled pilot in 40 adults over 65 found a B-cell autophagy measure rose after two weeks of 6 mg a day, but a T-cell measure did not[16]. The authors called this exploratory[16]. Both routes and the pilot are covered in our guide to how spermidine switches on autophagy.

The Evidence Ladder: what each species shows

Spermidine extended lifespan in yeast, worms, flies and mice in several studies, but the lifespan evidence stops at mice[4, 5, 17]. We found no dog studies, and lifespan extension has not been shown in people[10].

How we counted. On 8 October 2026, we searched PubMed for spermidine AND (lifespan OR longevity), which returned 226 records, 67 of them reviews. For each rung we added the species terms in the table. Counts overlap and include reviews, so they show how much has been written, not how many experiments were run. See the search note under References.

Rung PubMed records (base query plus...) Strongest finding What it does not show
Yeast 37 (AND (yeast OR Saccharomyces)) Spermidine "markedly extended" lifespan, and autophagy was needed for the effect[4]. The abstract gives no percentage. In yeast with damaged mitochondria, spermidine shortened lifespan, and this depended on the strain[18].
Worms (C. elegans) 28 (AND (elegans OR nematode)) Spermidine extended lifespan and switched on autophagy[4]. Blocking the worms' own spermidine production reduced the lifespan gain from fasting[9]. The abstract gives no effect size[4]. Worm results say little on their own about mammals.
Flies (Drosophila) 49 (AND (Drosophila OR flies); 35 with Drosophila alone) In a 2025 study, spermidine in food extended lifespan on both low- and high-protein diets[19]. In ageing flies, it also reduced memory decline[20]. In male flies of a long-lived strain, no dose extended lifespan, and the highest dose cut mean lifespan by 10.9% (66.2 vs 74.4 days)[21].
Mice 80 (AND (mice OR mouse)) Started at 18 months of age, spermidine in drinking water extended median lifespan by about 10%[5]. In an independent lab, lifelong use raised median survival from 26.9 to 33.3 months, about 24%[17]. Mouse lifespan results do not carry over to people automatically. In middle-aged male rats, spermidine did not extend median or maximum lifespan[22].
Dogs 0 (AND (dog OR dogs OR canine)) None. No PubMed record we found tests spermidine on ageing or lifespan in dogs. Anything about dogs.
Humans 147 (AND (humans[mh] OR human OR patients OR participants)) In the Bruneck cohort, each 1-SD higher dietary intake was associated with a 24% lower death rate (HR 0.76)[6]. Lifespan extension has not been shown in people[10]. Associations cannot show cause, a larger Japanese cohort was null, and the longest placebo-controlled trial missed its main endpoint[7, 23].
The spermidine evidence ladder, from yeast to humans Six rungs, bottom to top. Yeast, worms, flies and mice: lifespan extended in studies, with exceptions. A dashed line above mice marks where lifespan evidence stops. Dogs: no studies. Humans: diet associations and small trials, no lifespan trial. The spermidine evidence ladder Read from the bottom up. Counts are PubMed records, 8 Oct 2026. Humans 147 PubMed records No lifespan trial Diet associations, small trials Dogs 0 PubMed records No studies found Nothing to report yet Lifespan evidence stops here Mice 80 PubMed records Median life +10% to +24% Two labs; rats showed no gain Flies (Drosophila) 49 PubMed records Lifespan extended One long-lived strain: no gain Worms (C. elegans) 28 PubMed records Lifespan extended Needed autophagy Yeast 37 PubMed records Lifespan extended Not with damaged mitochondria
The Evidence Ladder. Lifespan gains were reported in yeast, worms, flies and mice, and the evidence stops after mice[4, 5, 17]. Counts are overlapping PubMed records, including reviews, from our 8 October 2026 search. On a small screen, scroll the figure sideways.

What the human evidence shows, honestly graded

In people, higher dietary spermidine was linked with lower death rates in some cohorts but not in others[6, 23]. The longest placebo-controlled supplement trial found no significant effect on its primary memory endpoint[7].

How we graded the evidence

A randomized controlled trial (RCT) assigns people by chance to the supplement or a placebo, so it can test cause and effect. A cohort study follows people over years and can only show an association.

Our grade What it means Can it show cause?
Stronger Randomized, placebo-controlled trial with a main outcome set in advance Yes, for that outcome
Moderate Large cohort study that follows people for years No, association only
Weak Small pilot trial, subgroup result, no placebo group, or product and dose not described No
Very weak No comparison group, or results reported only as change from baseline No

For rapamycin, metformin and other candidates graded by the strength of their human evidence, see our overview of how spermidine compares with other compounds studied for ageing.

Bruneck: the association most pages cite

The Bruneck study followed 829 adults aged 45 to 84 in Bruneck, Italy, from 1995 to 2015, with diet assessed four times[5, 6]. Before any adjustment, death rates were 40.5, 23.7 and 15.1 per 1,000 person-years from the lowest to the highest third of intake[6]. After adjusting for age, sex and calories, the estimated share who died over 20 years was 48%, 41% and 38%[6].

A hazard ratio (HR) compares how often an event happens in two groups; 0.76 means a 24% lower rate. The authors adjusted for lifestyle, other diet features and known risk factors[6]. After that, each 1-standard-deviation (SD) higher intake was associated with an HR of 0.76 (95% CI 0.67 to 0.86)[6]. A second cohort from Salzburg, called SAPHIR, showed a similar pattern after adjusting for age, sex and calories (HR 0.71, 95% CI 0.53 to 0.95)[6].

The authors wrote that the mortality gap between the top and bottom thirds of intake was similar to the gap linked with being 5.7 years younger[6]. That describes the size of a statistical link, not 5.7 extra years of life. Because Bruneck was observational, it cannot show that spermidine itself caused the lower death rate[6].

A 2016 analysis of the same cohort linked higher intake with lower blood pressure and fewer cardiovascular events[5]. Both papers draw on the same 829 people, so they are not independent confirmations[5, 6].

Other cohorts, including null results

Larger cohorts give a mixed picture. Residual confounding means other differences between groups that an analysis could not fully remove.

Cohort People What was measured Result
Takayama, Japan 29,079 adults aged 35 and over, 16 years Diet once, at baseline in 1992 Not significantly associated with all-cause or cause-specific mortality; the authors said their results did not support a benefit[23]
NHANES, United States 23,894 participants Estimated dietary spermidine Highest vs lowest quarter: HR 0.70 for all-cause mortality[24]
UK Biobank 184,732 adults, median 11.5 years Total polyamines, not spermidine alone The lowest fifth of intake had higher mortality, but the pattern was not "more is better"[25]
PLCO, United States 54,517 men Dietary spermidine A non-linear inverse link with all-cause mortality, which the authors said may reflect residual confounding[26]

Randomized trials

SmartAge is the longest published placebo-controlled spermidine trial we found. Its 100 participants, aged 60 to 90, felt their memory was slipping[7]. For 12 months, they took a wheat germ extract with about 0.9 mg of spermidine a day or a placebo[7]. SmartAge found no significant effect on its primary memory endpoint (difference −0.03; 95% CI −0.11 to 0.05; P = .47)[7]. It also found none on secondary outcomes in its main analysis[7]. Exploratory signals for inflammation and verbal memory would not stay significant after correcting for multiple tests, the authors noted[7].

A 95% confidence interval (CI) is the range of results that fit the data. If it includes zero, "no effect" is still a real possibility. SmartAge's 2018 pilot gave 30 adults aged 60 to 80 a wheat germ extract with 1.2 mg of spermidine a day for 3 months[27]. It reported a moderate memory effect, but the interval for the difference from placebo included zero (−0.01 to 0.35)[28]. The larger SmartAge trial, from the same group, did not confirm it[7, 28].

Study Design People, dose, length Main result Our grade
SmartAge, 2022[7] RCT 100 older adults; 0.9 mg/day; 12 months No significant effect on the primary memory endpoint Stronger design, null result
Memory pilot, 2018[28] Pilot RCT 30 older adults; 1.2 mg/day; 3 months Moderate effect size, but the CI included zero Weak
Immune pilot, 2026[16] Pilot RCT 40 adults over 65; 6 mg/day; 13 weeks Well tolerated (the main outcome); better vaccine responses only in an unevenly split subgroup Weak
Hair trial, 2017[29] RCT funded by the maker 100 healthy adults; dose not reported; 90 days More hair follicles in the growth phase Weak
Bread-roll study, 2021[30] Two doses, no placebo 92 nursing-home residents (85 tested); 3.3 vs 1.9 mg per roll, 6 rolls a week; 3 months Test scores rose in both groups Weak
Rice germ pilot, 2025[31] No placebo; first author is chief scientific officer of a nutraceutical ingredient company 12 adults; 1.5 or 3.3 mg/day; 8 weeks Changes from baseline in blood markers Very weak

In 2011, the European Food Safety Authority did not accept a proposed health claim linking spermidine to a longer hair-growth phase, because it judged the claim to concern a medical hair-shedding condition rather than a general health effect[32].

Does swallowed spermidine reach the blood?

Several studies found that blood levels barely moved.

  • In 12 healthy adults, 15 mg a day for 5 days raised blood spermine, a related polyamine, but not blood spermidine[33].
  • In 37 men aged 50 to 70, even 40 mg a day for 28 days barely changed polyamines in blood or urine[34].
  • In a 12-month Japanese study of 57 men, the 30 who ate polyamine-rich natto daily saw blood spermine rise modestly, while blood spermidine did not rise[35].
  • In rats given spermidine by stomach tube, about 70% to 80% of the dose stayed in its original form during absorption[36].
  • In the bread-roll study, which had no placebo group, blood spermidine rose only in the higher-dose group[30].
  • Blood levels are hard to read. In a cross-sectional study of 659 adults aged 21 to 81, higher blood spermidine was associated with a smaller hippocampus and thinner brain cortex on MRI scans; the authors suggested it might be an early marker of brain changes[37].

Who is studying spermidine?

Much of the best-known spermidine research comes from linked academic groups at the University of Graz in Austria and Charité in Berlin[4, 7]. Several of the most-cited papers disclosed financial ties to spermidine supplement makers[5, 7].

Group or study Where Disclosed ties
2009 multi-species study, 2016 mouse study, Bruneck[4–6] University of Graz, Austria; Bruneck led by the Medical University of Innsbruck, with Graz co-authors[6] Several authors held equity in a company founded in 2016 to develop natural food extracts[5]
2018 pilot and SmartAge[7, 27] Charité, Berlin, Germany That company supplied the extract; three authors held equity and one was its chief executive[7, 27]
eIF5A work and the 2026 immune pilot[15, 16] University of Oxford, UK The extract's maker supplied it and part-funded the 2026 pilot but had no input into the trial, the authors said; the senior author consults for that maker and one other company[16]
2024 fasting study[9] Graz and partners Equity in a supplement company and an autophagy biotech; two authors worked at the fasting clinic[9]
40 mg safety trial and 90-day rat study[34, 38] Industry Employees and funding from the ingredient's maker[34, 38]
Independent lifespan tests[17, 21] Texas A&M and South Alabama universities, US No spermidine-maker ties stated in the papers we read[17, 21]

The company tied to the Graz and Berlin groups also filed the only spermidine GRAS notice with the FDA, then asked the agency to stop evaluating it in 2020[39].

Two newer trials are led by other groups. POLYCAD, at Aarhus University Hospital in Denmark, randomly assigned 187 adults aged 65 and over with coronary artery disease to 24 mg a day or placebo for 48 weeks[40]. Results had not appeared in PubMed by 8 October 2026; a supplement company donated the capsules and, the investigators say, had no role[40]. REPROGRAM, at the University of Birmingham, UK, plans to give 15 mg a day for three weeks to adults aged 70 and over and measure senescent, or worn-out, cells in fat tissue[41].

Dose ranges in human studies, in brief

Human studies have used from about 0.9 mg of spermidine a day up to 40 mg a day of a purified spermidine salt, and only the lowest dose was tested for a full year against placebo[7, 34]. Typical diets supply roughly 5 to 15 mg a day[1].

Study Spermidine per day Form Length
SmartAge[7] About 0.9 mg 750 mg wheat germ extract 12 months
2018 safety trial[27] 1.2 mg 750 mg wheat germ extract 3 months
Immune pilot[16] 6 mg Wheat germ extract 13 weeks
Blood-level study[33] 15 mg Chlorella and soybean-based product 5 days
Safety trial in men[34] 40 mg (abstract does not say whether this is spermidine or the salt) Purified spermidine trihydrochloride 28 days
POLYCAD, results pending[40] 24 mg Capsules 48 weeks

In Great Britain, spermidine-rich wheat germ extract is authorised for adult food supplements at up to 6 mg of spermidine a day[42]. For diet versus trial doses in more detail, see our guide to how much spermidine per day studies used.

Safety in brief: who should be cautious

Small placebo-controlled trials of up to a year found no clear safety problems with spermidine[7, 16, 27, 34]. Trials left out people with wheat or gluten allergy, a history of cancer or blood-thinner use, and the UK authorisation excludes pregnant and breastfeeding women, so these groups should talk to a clinician first[27, 42].

  • Trials. In the 12-month SmartAge trial, adverse events were 58 with spermidine and 71 with placebo, but musculoskeletal complaints such as joint pain were more common with spermidine (11 vs 4 people)[7]. A 13-week trial of 6 mg a day and a 28-day trial of 40 mg a day reported no supplement-related adverse events[16, 34].
  • Cell growth. Polyamines are needed for cell growth, and cancer researchers note that polyamine metabolism is often disrupted in tumours[8]. The SmartAge team chose a low dose partly for this reason[7]. In the Takayama cohort, the authors reported a borderline, "suggestive" link between higher spermidine intake and cancer death in women (HR 1.38, 95% CI 0.99 to 1.93) that needs checking in other studies[23].
  • Regulators. Health Canada's ingredient database says more safety evidence is needed before spermidine can be used in natural health products[43]. The FDA stopped evaluating the only spermidine GRAS notice at the company's request, so it made no safety finding[39].

Important: The 2018 safety trial excluded people with wheat germ or gluten allergy, histamine intolerance or current or past cancer, and people taking anticoagulant or antiplatelet blood thinners, so it gives no safety data for these groups[27]. The UK authorisation excludes pregnant and breastfeeding women[42]. If any of these apply to you, talk to your clinician first.

Each trial's adverse events and the gluten question are covered in our full guide to spermidine side effects.

Where dietary spermidine comes from, in brief

Wheat germ, soybeans and natto, mushrooms and green peas are among the richest common sources[2, 3, 35]. In a 2026 Spanish analysis, vegetables were the largest single source of dietary spermidine[44].

Food Reported spermidine (mg per 100 g) Notes
Wheat germ powder About 22 to 34 Dry powder[2]
Natto (fermented soybeans) About 20 to 27 Commercial and polyamine-rich natto[35]
Dried soybeans About 13 to 21 German and Japanese analyses[3]
Mushrooms About 9 to 13 [3, 45]
Aged cheddar About 20 in one UK analysis Another aged cheese measured far less[3]
Green peas About 5 to 6.5 [3, 45]

Values vary widely between countries and studies[3]. Cooking matters too. In a Spanish lab study, some boiled or grilled foods lost up to about 37% of their spermidine, while sous-vide cooking caused no significant loss[45]. Our full table of spermidine-rich foods adds more foods and a sample day of eating.

Fasting and spermidine, in brief

In a 2024 study, blood spermidine rose by about 50% in one group of volunteers after 4 to 5 days of medically supervised fasting, and in lab yeast, worms and flies, blocking their own spermidine production reduced fasting's lifespan gain[9]. Whether a supplement can stand in for fasting in people has not been shown[9, 33].

A 2018 review in Science described spermidine as a candidate "caloric restriction mimetic", a compound that might copy some cellular effects of eating less[46]. But in a small trial, swallowing 15 mg a day did not raise blood spermidine[33]. Our page on spermidine, autophagy and fasting sorts the established from the speculative.

How to judge a spermidine supplement label

Studies have used wheat germ extract, a purified spermidine salt, rice germ extract and a chlorella and soybean product, and we found none that compared these forms head to head[7, 31, 33, 34]. So there is no proven best spermidine supplement, and a label is best judged on what it discloses.

What to check Why it matters What a clear label shows
Spermidine per serving, not extract weight In trials, 750 mg of wheat germ extract gave only about 0.9 to 1.2 mg of spermidine[7, 27] Milligrams of spermidine itself per serving
Source and form Forms include wheat germ, rice germ and a purified salt, spermidine trihydrochloride[31, 34] The source, and whether milligrams mean spermidine or the salt; the 40 mg trial's abstract did not say[34]
Standardization The same 750 mg extract dose was reported as 1.2 mg of spermidine in 2018 and 0.9 mg in 2022[7, 27] A tested amount of spermidine per gram
Wheat and gluten Wheat is a major US allergen, and allergen labelling rules apply to supplements[47]. A product sold as spermidine trihydrochloride was recalled in 2025 for undeclared wheat[48] A clear wheat statement. In the US, a "gluten-free" claim means less than 20 parts per million of gluten[49]
Third-party testing The 2025 recall came to light through product testing[48] A certificate of analysis from an independent lab
Dose and claims Long trials used low doses, and higher doses were tested only for weeks[7, 16, 34] A dose within tested ranges and no promise of longer life

In Great Britain, the authorised wheat germ ingredient must be labelled "spermidine-rich wheat germ extract"[42].

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Frequently asked questions

What are the benefits of taking spermidine?

No benefit of taking spermidine supplements has been confirmed in people so far. The longest placebo-controlled trial, SmartAge, gave about 0.9 mg a day for 12 months and found no significant effect on its primary memory endpoint[7]. A 40-person pilot reported better vaccine responses only in a subgroup of poor responders[16]. A maker-funded hair trial reported more growing hair follicles but did not state the spermidine dose[29].

Does spermidine help people live longer?

Spermidine has extended lifespan only in lab organisms such as yeast, worms, flies and mice, and this has not been shown in people[4, 5, 10]. In the Bruneck cohort of 829 adults, higher dietary spermidine was associated with lower mortality over 20 years[6]. A Japanese cohort of about 29,000 adults found no significant link, and associations like these cannot show cause[23].

What is the best form of spermidine to take?

Studies of spermidine used wheat germ extract, a purified salt called spermidine trihydrochloride, rice germ extract and a chlorella and soybean product, and we found none that compared forms directly[7, 31, 33, 34]. When choosing a spermidine supplement, check the milligrams of spermidine itself, not extract weight, and look for a clear wheat and gluten statement. A trihydrochloride product was recalled in 2025 for undeclared wheat[48].

Has spermidine been studied in dogs?

Spermidine has not been tested on ageing or lifespan in dogs, based on our PubMed search on 8 October 2026. We screened all 102 records that mention spermidine and dogs, and none tested it for ageing, healthspan or lifespan. In other mammals the results are mixed: spermidine in drinking water extended median lifespan in mice in two labs but not in middle-aged male rats, and none of this shows what it would do in dogs[5, 17, 22].

Does spermidine come from sperm?

The name spermidine comes from spermine, a related polyamine, not from spermidine being discovered in sperm. A 1927 paper named spermidine after isolating it from ox pancreas, where it occurred alongside spermine and had a related chemical structure[50]. Many foods contain spermidine, and wheat germ, soybeans and mushrooms are among the richest sources measured[1, 2].

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Search note for the Evidence Ladder counts: PubMed search: spermidine AND (lifespan OR longevity), run through NCBI E-utilities on 8 October 2026. The base query returned 226 records, 67 of them tagged as reviews. Species counts add the terms shown in the ladder table. We also screened all 102 records matching spermidine AND (dog OR dogs OR canine); none tested spermidine on ageing, healthspan or lifespan in dogs.

This content is for education only and is not medical advice. Talk to your healthcare provider before starting any supplement, especially if you are pregnant, nursing, take medication, or have a medical condition.

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