Spermidine

Spermidine (N-(3-aminopropyl)butane-1,4-diamine) is a naturally occurring triamine polyamine present in all living cells and in the human diet, principally from wheat germ, soybeans, fermented foods, and aged cheeses. First observed as a crystalline component of human semen by Antonie van Leeuwenhoek in 1678, spermidine was structurally characterized in the early twentieth century and subsequently identified as a central metabolite in polyamine biosynthesis, formed by the transfer of an aminopropyl group from decarboxylated S-adenosylmethionine to putrescine by the enzyme spermidine synthase. The compound participates in multiple essential cellular processes including chromatin structure modulation, translational regulation through hypusination of eukaryotic translation initiation factor 5A (eIF5A), cell proliferation, and the induction of macroautophagy.

The geroprotective potential of spermidine was established in a series of investigations beginning with the Eisenberg et al. (2009) demonstration that exogenous spermidine extends chronological lifespan in yeast, nematodes, and flies through autophagy-dependent mechanisms [1]. The molecular basis for autophagy induction was subsequently characterized as inhibition of the acetyltransferase EP300 (p300), resulting in hypoacetylation of core autophagy proteins (ATG5, ATG7, ATG12, and LC3) and convergent deacetylation of cytoplasmic proteins that parallels the acetylproteome shifts produced by caloric restriction and by other caloric restriction mimetics [2, 3]. Spermidine thereby occupies a mechanistically distinct position among autophagy inducers: it acts through acetyltransferase inhibition rather than through mTOR suppression (rapamycin), AMPK activation (metformin), or sirtuin activation (resveratrol).

The landmark Eisenberg et al. (2016) study in Nature Medicine demonstrated that oral spermidine supplementation extends lifespan in mice, reduces cardiac hypertrophy, preserves diastolic function in aged animals, delays progression to heart failure in salt-sensitive hypertensive rats, and enhances cardiac autophagy, mitophagy, and mitochondrial respiration in an ATG5-dependent manner [4]. Epidemiological analysis of the Bruneck Study cohort (n = 829, 20-year follow-up) within the same report identified a significant inverse association between dietary spermidine intake and cardiovascular mortality, all-cause mortality, and cancer-related mortality, with the highest-intake tertile exhibiting a risk reduction comparable to approximately 5.7 years of aging [4, 5]. These findings were extended by Kiechl et al. (2018), who confirmed the inverse relationship between dietary spermidine and mortality in a larger epidemiological analysis [5].

Clinical investigation of spermidine has advanced through several randomized controlled trials. The SmartAge trial (Wirth et al. 2018, 2022) evaluated spermidine-rich wheat germ extract supplementation in older adults with subjective cognitive decline; a 3-month pilot study reported modest memory improvement, while a 12-month Phase IIb trial did not demonstrate significant modification of memory performance or biomarkers at the studied dose [6, 7]. The POLYCAD trial (NCT05128331), a Danish randomized double-blind placebo-controlled study of 24 mg/day spermidine in 187 elderly patients with coronary artery disease, completed enrollment in 2025 and represents the first dedicated cardiovascular outcomes trial for spermidine [8]. Additional trials have examined metabolic responses to spermidine supplementation (NCT05459961) and dose-escalation safety in aging populations.

Pharmacokinetic studies have revealed that dietary spermidine is rapidly absorbed from the intestinal lumen but is subject to extensive presystemic conversion to spermine, resulting in minimal elevation of circulating spermidine concentrations following oral supplementation at doses up to 40 mg/day [9, 10]. This observation suggests that the biological effects of oral spermidine may be mediated through local gastrointestinal and first-pass hepatic mechanisms, through polyamine interconversion in target tissues, or through modulation of gut microbiota-derived polyamine pools rather than through systemic plasma exposure.

Spermidine supplementation has demonstrated a favorable safety profile in all completed human studies. No serious adverse events attributable to the compound have been reported. The European Food Safety Authority authorized spermidine-rich wheat germ extract as a Novel Food in 2021 with a recommended upper intake of 6 mg/day of spermidine [11]. Higher doses (up to 40 mg/day of purified spermidine for 28 days) have been evaluated without significant adverse effects in healthy older men [10]. This monograph reviews the chemistry, biosynthesis, and dietary sources of spermidine; the molecular pharmacology of autophagy induction, eIF5A hypusination, and anti-inflammatory signaling; pharmacokinetics; the preclinical and clinical evidence base across cardiovascular, cognitive, and geroprotective applications; sourcing and quality verification; reconstitution and handling; stack-interaction considerations; adverse events and safety signal; and a comparative assessment of five geroprotective and autophagy-inducing compounds (rapamycin, resveratrol, nicotinamide mononucleotide, urolithin A, and metformin) against spermidine on five competency standards.