High-dose spermidine supplementation is useless because it does not increase spermidine levels in blood plasma or saliva in healthy adults.

noli's read

This advice is based on a randomized controlled trial (RCT) published in 2024 in 'Nature Communications', which examined the pharmacokinetics of spermidine. The results show that even with high doses, the systemic concentration does not rise significantly in participants, suggesting rapid degradation or sequestration by tissues. This observation is solid because it comes from a rigorous protocol, contradicting the idea that direct oral intake mechanically elevates circulating levels. It is important to note that this study focuses on blood and salivary markers, not on potential intracellular cellular effects or long-term benefits on autophagy. The assertion that one should 'stop spending money' is a logical interpretation based on the absence of a measurable increase in classic markers. This is an important nuance: the absence of evidence for a plasma increase does not necessarily mean the total absence of a biological effect, but it seriously calls into question the current supplementation strategy.

the sources

No named source held this one up — that absence is part of the verdict.