Urolithin A vs Spermidine

Both are studied as triggers of cellular clean-up. Urolithin A, produced by gut bacteria from ellagitannins, targets mitophagy (removal of damaged mitochondria); spermidine induces general autophagy.

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Urolithin A

A gut-microbiome metabolite of ellagitannins (pomegranate, berries, nuts) that stimulates mitophagy — the recycling of damaged mitochondria.

BEST STUDIED FOR

Mitochondrial & longevity

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	Urolithin A	Spermidine
The key difference	Gut-microbe metabolite inducing mitophagy	Polyamine inducing autophagy
Class	Mitochondrial & longevity	Mitochondrial & longevity
Mechanism	Only some people’s gut bacteria convert dietary ellagitannins to urolithin A.	Spermidine inhibits acetyltransferases (notably EP300), promoting autophagy; fasting-induced autophagy depends on it in model organisms.
Status	Several randomised human trials in middle-aged and older adults and athletes; marketed as a supplement.	Strong preclinical lifespan and cardioprotection data (mice); human evidence is mostly observational and small trials. Available in food-derived supplements.
Reported safety signals	Trials report it as well tolerated over the study periods.	Reviews describe a good safety record at dietary-type intakes; long-term human data are limited.
A key study	A randomised placebo-controlled trial measured muscle strength and mitochondrial biomarkers with urolithin A in middle-aged adults. (Cell Rep Med 2022, PMID 35584623)	Reviews spermidine as a caloric-restriction mimetic with anti-ageing effects across models. (Science 2018, PMID 29371440)

Urolithin A for mitochondrial-quality research; spermidine for broad autophagy research. Both are discussed here strictly as research compounds; nothing on this page is medical advice or a dosing guide.

REFERENCES (PUBMED)

[Urolithin A] Urolithin A improves muscle strength, exercise performance, and biomarkers of mitochondrial health in a randomized trial in middle-aged adults — Cell Rep Med 2022. PMID 35584623
[Urolithin A] Effect of Urolithin A Supplementation on Muscle Endurance and Mitochondrial Health in Older Adults: A Randomized Clinical Trial — JAMA Netw Open 2022. PMID 35050355
[Urolithin A] Effect of the mitophagy inducer urolithin A on age-related immune decline: a randomized, placebo-controlled trial — Nat Aging 2025. PMID 41174221
[Spermidine] Spermidine in health and disease — Science 2018. PMID 29371440
[Spermidine] Cardioprotection and lifespan extension by the natural polyamine spermidine — Nat Med 2016. PMID 27841876
[Spermidine] Spermidine is essential for fasting-mediated autophagy and longevity — Nat Cell Biol 2024. PMID 39117797

FREQUENTLY ASKED

What is the difference between Urolithin A and Spermidine?

Both are studied as triggers of cellular clean-up. Urolithin A, produced by gut bacteria from ellagitannins, targets mitophagy (removal of damaged mitochondria); spermidine induces general autophagy.

What is the regulatory status of Urolithin A and Spermidine?

Urolithin A: Several randomised human trials in middle-aged and older adults and athletes; marketed as a supplement. Spermidine: Strong preclinical lifespan and cardioprotection data (mice); human evidence is mostly observational and small trials. Available in food-derived supplements.

What safety signals have been reported?

Urolithin A: Trials report it as well tolerated over the study periods. Spermidine: Reviews describe a good safety record at dietary-type intakes; long-term human data are limited.

Which studies is this comparison based on?

For Urolithin A: “Urolithin A improves muscle strength, exercise performance, and biomarkers of mitochondrial health in a randomized trial in middle-aged adults” (PMID 35584623); “Effect of Urolithin A Supplementation on Muscle Endurance and Mitochondrial Health in Older Adults: A Randomized Clinical Trial” (PMID 35050355); “Effect of the mitophagy inducer urolithin A on age-related immune decline: a randomized, placebo-controlled trial” (PMID 41174221). For Spermidine: “Spermidine in health and disease” (PMID 29371440); “Cardioprotection and lifespan extension by the natural polyamine spermidine” (PMID 27841876); “Spermidine is essential for fasting-mediated autophagy and longevity” (PMID 39117797).