Spermidin boosts autophagy and mitochondrial function, but human clinical evidence remains mixed

Researchers reviewed the geroprotective properties of spermidine across mechanistic, preclinical, and clinical evidence. Spermidin levels naturally decline with age in human blood cells. The review identifies the eIF5A-TFEB axis as a central mechanism: spermidine promotes hypusination of eIF5A, which in turn supports translation of TFEB and ATG7, driving autophagic flux. In preclinical models, a 6-month spermidine regimen attenuated age-associated phenotypes in mice and reduced telomere attrition. Spermidin also improved mitochondrial function and ATP production in cell and animal models. On the human side, 3.3 mg/day from rice germ extract improved biomarkers of autophagy and cardiometabolic health. High-purity spermidine at 40 mg/day for 28 days was safe and well-tolerated in older men. However, the 12-month Phase IIb SmartAge trial in older adults with subjective cognitive decline found no improvement in memory or biomarkers versus placebo. Exploratory analyses suggested possible effects on verbal memory and tissue inflammation. Population studies linked higher dietary spermidine intake to lower cardiovascular and cancer mortality, though effect sizes were not reported. The authors caution that spermidine should not be considered for routine preventive use in longevity medicine until larger, long-term trials confirm efficacy and optimal dosing.

Spermidin is a versatile, multi-targeted candidate geroprotector, but evidence needed for routine human use is still emerging.