Urolithin A for four weeks did not improve blood-vessel function in adults with obesity

Urolithin A has become a popular “mitochondria” supplement, so it is worth checking what the human trials actually show. A small randomized trial published in JAMA Network Open on October 9, 2026 tested it in middle-aged adults with obesity. After four weeks, it found no significant improvement in how well their blood vessels worked. It did find a difference in a brain-activity scan measure, which the authors say needs more study.

What the researchers did

Urolithin A is a compound that gut bacteria make from certain plant polyphenols. The authors describe it as a “mitophagy activator”, meaning it may help cells clear out worn mitochondria (the energy-producing parts of cells). Mitochondrial problems are thought to contribute to blood-vessel dysfunction in obesity, which was the reason for the trial.

At a single site, the University of Oklahoma Health Campus, researchers recruited adults aged 40 to 64 with a body mass index of 30 or more between October 2023 and May 2025. Participants were randomly assigned 1:1 to 1,000 mg of urolithin A or placebo, double-blind, for four weeks. The main outcome was flow-mediated dilation (FMD), a standard test of how well an artery widens after a brief period of restricted blood flow. Secondary outcomes included other blood-vessel tests and brain-blood-flow responses while doing thinking tasks.

What they found

• Who took part: 50 people (25 on urolithin A, 25 on placebo). Average age was 50.7, average BMI 38.3, and 74% were women. Seven people (14%) were lost to follow-up.
• Main result: FMD did not differ significantly between groups. It changed by an average of 0.3% in the placebo group and 1.3% in the urolithin A group, with a lot of person-to-person variation (SDs 5.1% and 7.6%).
• Other blood-vessel tests: no significant effect.
• Brain scan: the urolithin A group showed significantly greater task-evoked blood-flow responses in the brain than placebo, but task performance itself did not change.
• Tolerability: the authors describe the supplement as well tolerated and feasible.

The authors concluded that four weeks of urolithin A did not significantly improve peripheral endothelial function, and that the brain blood-flow finding “warrants further investigation”.

What this means for you

What this means for you

• What was studied: 1,000 mg of urolithin A a day for four weeks.
• Who was studied: adults aged 40 to 64 with obesity (average BMI 38), not the general population.
• What it shows: no improvement in the main blood-vessel test. The brain-flow signal is an early lead, not a benefit people could feel.
• Evidence strength (our simple scale: very low, low, moderate, high): low. It is a well-designed trial but small and short, and the main result was neutral.
• Read more in our beginner’s guide to urolithin A.

How strong is this evidence?

This was a randomized, double-blind, placebo-controlled trial, but only 50 people were included and the treatment lasted just four weeks. The results may not apply to people without obesity or to longer-term use, and a small study can miss real effects. The brain-flow result was a secondary outcome, so it should be treated with more caution than a primary result. The authors report no conflicts of interest. We read the abstract and the PubMed record; we did not read the full text, and did not see the funding statement.

Sources

• Urolithin A and Endothelial and Cerebrovascular Function in Middle-Aged Adults With Obesity: A Randomized Clinical Trial. JAMA Network Open, published October 9, 2026. DOI: 10.1001/jamanetworkopen.2026.38047 / PubMed 42853569 / JAMA Network page (abstract read)
• Trial registry: ClinicalTrials.gov NCT05921266 (registration number from the abstract; registry page not opened)

This article is for information only and is not medical advice. Speak to a healthcare professional before changing medication or supplements.