A new randomized trial in JAMA Network Open tested whether 1,000 mg of urolithin A (UA) per day could improve blood vessel function in middle-aged adults with obesity. On its main question, it did not. But a secondary brain measure moved, and that is what makes the study worth a closer look.
The Short Version
- Primary endpoint: null. Brachial artery flow-mediated dilation (FMD) did not differ between UA and placebo after four weeks.
- Peripheral secondary outcomes: also null. Hand and fingertip microvascular measures showed no treatment effect.
- Brain signal: positive, but secondary. Task-evoked cerebrovascular hemodynamic responses were significantly greater with UA, while task performance did not change.
- Tolerability: acceptable. The authors describe supplementation as well tolerated and feasible.
- Verdict: hypothesis-generating. It does not show that UA protects arteries or improves cognition.
Why Test Urolithin A in Obesity?
Obesity affects nearly half of US adults in midlife and is a major driver of chronic disease. One proposed contributor is mitochondrial dysfunction in the cells lining blood vessels, which can impair endothelial function and raise cardiovascular risk.
Urolithin A is a metabolite produced by gut microbes from polyphenols found in pomegranates and some nuts and berries. Not everyone makes it efficiently, which is part of why it is sold as a supplement. It is described as a mitophagy activator, meaning it supports the cellular process that clears out damaged mitochondria. Earlier human work has suggested it is safe and may benefit mitochondrial health. The Oklahoma team asked whether that cellular promise would show up as better vascular function in people with obesity.
How the Trial Worked
The study was a single-site, double-blind, placebo-controlled randomized trial at the University of Oklahoma Health Campus, running from October 2023 to May 2025.
| Feature | Detail |
|---|---|
| Participants | 50 adults, 40-64 years, BMI 30 or higher |
| Mean age | 50.7 years |
| Mean BMI | 38.3 |
| Sex | 74% female |
| Intervention | 1,000 mg UA daily vs placebo, 1:1 allocation |
| Duration | About 28 days |
| Dropout | 7 participants (14%) |
| Primary outcome | Change in brachial artery FMD |
| Analysis | Intention-to-treat |
FMD is a standard ultrasound-based test of how well an artery widens in response to increased blood flow. Lower values generally point to poorer endothelial health.
What Happened to the Arteries
Nothing statistically meaningful. FMD changed by 0.3% in the control group and 1.3% in the UA group. The standard deviations (5.1% and 7.6%) dwarf that gap, so the difference is well within noise.
The complementary peripheral measures told the same story. Reactive hyperemia-induced perfusion in the dorsal hand, acute reperfusion, and the fingertip reactive hyperemia index showed no significant treatment effect. Several different tools pointed the same way, which makes a missed measurement less likely, though not impossible with a small sample.
The Brain Finding
The cerebrovascular result is the surprise. Using t-contrast maps of task-evoked hemodynamic responses, the researchers found significantly greater responses after UA than after placebo. The mean β coefficient was -1.43 (SD 5.26) in the control group and 15.53 (SD 13.02) in the UA group.
In plain terms, the brain's blood-flow response to a cognitive task looked stronger in people taking UA. That is a measure of neurovascular coupling, the process by which active brain regions get more blood.
There are important caveats:
- It was a secondary outcome. The trial was built around FMD. Secondary findings are more vulnerable to chance, especially when several outcomes are tested.
- Task performance did not change. A stronger hemodynamic response did not translate into better performance on the task. Whether it means anything functionally is unknown.
- The groups moved in opposite directions. The control group's slightly negative value and the UA group's large positive one, with wide variability, call for replication before anyone interprets the size of the effect.
- It is a small, single-site study. Fifty participants, mostly women, with high average BMI, limits how far the findings generalize.
Why a Null Peripheral Result Matters
It is tempting to focus on the brain and skip over the miss. That would be a mistake. If UA improved mitochondrial health in endothelial cells enough to matter, peripheral FMD is where many researchers would expect to see it. The absence of an effect suggests that, at least over four weeks in this population, systemic vascular benefit is not a given.
Four weeks is also short. Vascular remodeling and metabolic adaptation can take longer, and the trial cannot say whether a longer course would change the artery results. A null result in a short trial is not proof of no effect, but it should lower expectations.
Practical Takeaways
Dose. The trial used 1,000 mg of UA daily, at the upper end of what is typically studied and sold in supplement form, including branded products like Mitopure. The findings apply to that dose and formulation approach, not to low-dose or food-derived exposure.
Who might care. The population was middle-aged adults with obesity. People hoping UA will repair arterial function in this group do not get support from this trial. People interested in brain vascular health have a lead worth following, not an actionable result.
What to expect. Over four weeks, do not expect measurable improvement in artery function. Any brain-blood-flow change here was detected with research imaging, and it did not produce better task performance. There is no evidence of a perceptible cognitive benefit.
Safety. The authors report good tolerability and feasibility, with a 14% dropout over four weeks. The abstract does not detail adverse events, so check the full paper for specifics.
Not a substitute. Nothing here suggests UA can stand in for weight management, exercise, blood pressure control, or other proven cardiovascular strategies.
What Comes Next
The authors conclude that the cerebrovascular effect "warrants further investigation." The next steps are clear. Researchers need larger trials that pre-specify brain hemodynamics as the primary outcome, longer durations, and cognitive endpoints that capture real-world function. Trials should also test whether the signal appears in people without obesity and whether it depends on dose.
Bottom Line
This is a well-designed small trial with an honest null on its main question and an intriguing, unproven signal on a secondary one. Urolithin A did not improve artery function in four weeks, and the brain finding is a reason to run the next study, not a reason to buy the supplement for cognition.
