Spermidine supplements are fairly cheap. Most of the benefits clamed are from association not actual RTCs. “linked” “associated”
Do I want to add still another supplement with only marginal evidence to my already long stacks of supplements?
One actual RTC: "Findings In this randomized clinical trial that included 100 older adults, spermidine supplementation over 12 months did not result in a significant beneficial effect on mnemonic discrimination performance as compared with placebo.
Meaning Longer-term spermidine supplementation with an increased daily supply of spermidine by about 10% did not modify memory and other biomarkers in a group of older adults at risk for Alzheimer disease. ref
Some results from ChatGPT 5.2:
“Current evidence of the effect of spermidine on cognitive function shows inconsistent results based on a few studies with low spermidine doses and a small number of participants. Further evidence is needed to assess its actual effect.”
Strongest human evidence is associational, not proof of slowed aging.
Several large observational studies find that people with higher dietary spermidine intake tend to have lower all-cause and cardiovascular mortality. This is interesting, but it cannot prove spermidine caused the benefit (diet pattern, lifestyle, and “healthy user” effects can confound results). ref2
"A short pharmacokinetic study also tested 15 mg/day for 5 days and showed shifts mainly in related polyamines rather than a big rise in circulating spermidine itself (the body tightly regulates these levels).
typical diet already contains spermidine.
Average dietary intake varies widely by diet pattern and country; a commonly cited range is roughly ~7–25 mg/day.
That means many supplements (especially 1–3 mg/day products) are sometimes below what you might get from a spermidine-rich diet—though bioavailability and matrices differ. ref3