Does supplementing actually raise spermidine?

Not in blood. At 15 mg per day in 12 volunteers, plasma spermidine was unchanged while spermine rose significantly (Senekowitsch 2023). At 40 mg per day in 37 men, the effect on circulating polyamines is described as minimal (Keohane 2024).

Is spermidine dangerous?

Tolerability data is reassuring: 40 mg per day for 28 days produced no significant change in clinical, lipid, chemistry or haematological parameters versus placebo, and no product-related adverse events, in men aged 50 to 70.

When should it be taken?

No trial compares timing. Published protocols administer a single daily dose without specifying an optimal moment.

Why do so many positive studies get reported then?

Because most are animal models or epidemiological data on dietary intake (Madeo 2018). Those results do not automatically transfer to oral supplementation in humans — which is precisely what the pharmacokinetic work has now shown.

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Spermidine: what dose, and why your blood levels don't rise

Published 8/20/2026 · by VEXTA Team

What the pharmacokinetics actually measured

For years, spermidine has been sold on a simple chain of reasoning: levels fall with age, you supplement, levels come back up. That middle step had never been tested in humans.

Senekowitsch 2023 (Nutrients, DOI 10.3390/nu15081852) tested it for the first time: a randomised, placebo-controlled, triple-blinded two-arm crossover trial, two 5-day intervention phases separated by a 9-day washout, in 12 healthy volunteers taking 15 mg of spermidine per day. Quantification by liquid chromatography–mass spectrometry.

The result: compared with placebo, supplementation significantly increased plasma spermine but did not affect spermidine or putrescine levels.

In other words: you supplement spermidine, and a different polyamine is what goes up.

A second study, at a far higher dose

Keohane 2024 (Nutrition Research, DOI 10.1016/j.nutres.2024.09.012) tested a high-purity spermidine trihydrochloride in 37 healthy men aged 50 to 70, at 40 mg per day — nearly three times the earlier dose — over 7 and 28 days, double-blind against placebo.

Two takeaways. On safety: no significant changes in clinical, lipid, chemistry or haematological parameters versus placebo, high compliance, no product-related adverse events. On effect: the study's own title is explicit — minimal effects on circulating polyamines.

Two independent teams, two very different doses, the same conclusion on the blood marker.

How to read this honestly

This is not "spermidine does nothing". It is more interesting than that, and more uncertain.

Three readings coexist, none of them settled:

Plasma may be the wrong compartment: polyamines are overwhelmingly intracellular, and a blood measurement can miss what happens in tissue
Spermine may be the carrier: ingested spermidine is converted, and any effect would run through it
The effects seen in epidemiology and animal work (Madeo 2018, Science) may simply not transfer to oral supplementation in humans

What can be stated without risk of error: if a product promises to "restore your spermidine levels", it asserts something the only two published pharmacokinetic studies contradict.

So what dose?

Commercial supplements typically deliver 0.5 to 1.2 mg per capsule, often as wheat germ extract. The pharmacokinetic studies work at 15 and 40 mg — an order of magnitude higher.

There is therefore no established effective human dose, because the intermediate marker itself does not move. Commercial doses are justified by safety and by consistency with dietary intake, not by a demonstration of efficacy.

On tolerability the data is solid: 40 mg per day for 28 days produced no safety signal in men aged 50 to 70.

Sources

Questions fréquentes

Supplements typically deliver 0.5 to 1.2 mg per capsule. Published pharmacokinetic studies used 15 mg (Senekowitsch 2023) and 40 mg (Keohane 2024) per day. No effective human dose is established, because the blood marker does not move usefully.