Urolithin A

Urolithin A is a member of the urolithins, a group of organic compounds of the benzo-coumarin class that are produced when gut bacteria transform dietary ellagitannins and ellagic acid. These precursor polyphenols are found in pomegranates, strawberries, raspberries, blackberries, walnuts, muscadine grapes and oak-aged wines, but urolithin A itself is not present in any food; it is generated in the gut from those precursors by the resident microbiota, with species such as Gordonibacter implicated in the conversion ^[1].

A notable feature of urolithin A is that people vary greatly in their ability to make it. The efficiency with which the gut microbiome converts ellagitannins into urolithin A differs substantially between individuals, and some produce little or none, which helps explain why the health effects of ellagitannin-rich foods differ from person to person ^[1]. Once formed, urolithin A is absorbed and extensively conjugated by glucuronidation, methylation and sulfation before circulating and being excreted in urine ^[1].

Research on urolithin A has centred on the mitochondria. It has been described as a mitophagy activator, meaning it promotes the clearance of damaged mitochondria and the renewal of the mitochondrial pool, and preclinical work linked it to improved muscle function in aged animals. A first-in-human trial found that oral urolithin A was safe, reached the bloodstream and produced a molecular signature of improved mitochondrial and cellular health in elderly people ^[2], and a later randomised clinical trial in older adults reported that supplementation was well tolerated and improved measures of muscle endurance and certain plasma biomarkers, though some primary outcomes were not met ^[3].

Urolithin A is marketed as a dietary supplement, including under the brand name Mitopure, and in 2018 United States regulators recognised specific preparations as generally recognised as safe for use in foods at defined amounts. Toxicity studies have not identified specific adverse effects from dietary intake, and early human studies report good tolerability with only mild side effects ^[2][3].

Urolithins also show antioxidant activity in laboratory assays, though urolithin A is a comparatively weaker antioxidant than some of its relatives ^[4]. Overall it is best understood as a gut-derived metabolite whose most distinctive property is its action on mitochondrial quality control.

Human trials show it is well tolerated with a good safety profile at studied doses. Side effects are minimal and mostly mild GI. Long-term data are still accumulating. It is generally regarded as low risk.