Urolithin A helped stiff hearts in mice. In people, the evidence is for muscle

Evidence check, September 29, 2026

The claim: "Urolithin A, the pomegranate compound, improves heart function by up to 80%."

Our grade: Unproven for people. The heart result is in mice and lab-grown human heart tissue, not patients. In people, small trials found better muscle endurance and leg strength, not a longer walk.

Ruth is 66. She saw the headline on her phone over breakfast: "Pomegranate compound improves heart function by up to 80%." She already drinks a glass of pomegranate juice most mornings. Her brother has heart failure, and she gets more winded on hills than she used to.

Is that glass of juice doing anything for her?

The answer turns on three things: what the heart study really tested, what the human trials found, and something happening in Ruth's gut.

Where the claim came from

On August 19, 2026, a team at King's College London published a study in Science Advances on urolithin A and heart failure [1]. The university's press release said it "improved heart function by up to 80%" [2], and ScienceDaily ran that headline on September 28 [3]. Rhonda Patrick has covered urolithin A on FoundMyFitness for years, as a way to help the body clear out worn-out mitochondria, the small power plants inside each cell [4].

Urolithin A isn't in pomegranates. Pomegranates, walnuts and raspberries contain ellagitannins, and some gut bacteria turn those into urolithin A. It's also sold as a pill: Mitopure, made by Amazentis and sold by its brand Timeline, 500 mg in two softgels [5].

Clue one: the heart result is real, and it's in mice

The study was about HFpEF, heart failure with preserved ejection fraction. The heart squeezes normally but has become stiff, so it can't relax and fill well between beats. It's about half of all heart failure, and there are few good treatments [2].

The team gave mice a stiff-heart condition with a kidney operation, a salt-retaining hormone and a high-fat diet. From day 21, the mice got urolithin A by mouth every day for 7 days, 5 to 7 mice per group [1]. Their hearts relaxed and filled better, had less scarring, and the mice ran longer on a treadmill. The team also found how it works: urolithin A acts on one spot on a heart-relaxing protein called PKGIα. Mice bred without that spot didn't benefit.

Then they tested heart tissue grown from one person's stem cells, 6 samples. Within 2 hours, the time the tissue took to relax fell by 32% to 40%, and the time to contract fell by 34% to 49%, with no loss of strength [1]. The paper doesn't say where the "up to 80%" comes from.

The British Heart Foundation, which paid for the work, put it plainly: the benefits "have so far been seen in animals and engineered human tissue, so clinical trials involving people are needed" [2].

That's a good first step. It isn't a treatment yet.

Clue two: in people, the trials are about muscle

Urolithin A has been tested in people, but for muscle, not the heart. All of these trials were funded by Amazentis.

In Seattle, 66 adults aged 65 to 90 took 1,000 mg a day or a placebo for 4 months [6]. The main goals missed: walking distance in 6 minutes rose 61 meters on urolithin A and 43 meters on placebo, too close to call, and the muscles' energy output didn't change. But in a test of how many times a muscle can contract before it tires, the hand muscle's count rose by 95 on urolithin A against 12 on placebo, and a leg muscle's by 41 against 6. A blood marker of inflammation, CRP, went down.

In a second trial, 88 overweight, untrained adults aged 40 to 64 took 500 mg, 1,000 mg or a placebo for 4 months [7]. The main goal, peak power on a bike, didn't improve. The hamstrings got about 12% stronger on both doses. Fitness (peak oxygen use) and grip strength leaned the right way but weren't clear results.

A 2026 review pooled 5 randomized trials with 236 people [8]. For the one test it could combine, the 6-minute walk, people on urolithin A walked 17 meters farther, a difference that could still be chance. The reviewers rated the evidence low and called the strength and endurance results "exploratory."

So in people, urolithin A has made muscles last longer and pull a bit harder in small, short trials. It hasn't yet made anyone walk farther.

Clue three: your gut bacteria decide

Here's the part the headline leaves out. Whether pomegranate juice gives you urolithin A depends on which bacteria you carry. About 1 in 10 people make none at all, and 2 or 3 in 10 make mostly other urolithins [9].

In a study of 100 adults who drank pomegranate juice, only about 40% had a meaningful level of urolithin A in their blood the next day [10]. A 500 mg capsule gave more than 6 times as much as a glass of juice did. To match it, you'd need about 1.5 liters of juice (about 6 glasses). That study was also run by Amazentis.

So back to Ruth. Her morning juice may give her some urolithin A, or almost none; there's no easy way to know. And the heart benefit she read about hasn't been shown in a single person yet. If she wants to try urolithin A, the best human evidence is for her muscles, not her heart.

Our grade

The case for the other side: the heart study didn't just show a benefit, it found the exact protein urolithin A works through. That kind of detail makes a real effect more likely. Urolithin A has been safe in every human trial so far, and it lowered CRP in two of them. And for a heart that can't relax, better relaxation in human tissue is the right thing to measure.

The case against: mice aren't people, and a week of treatment isn't years. The human trials are small and short, their main goals missed, and the company that sells Mitopure paid for all of them.

What would change the grade: a randomized trial of urolithin A in people with stiff-heart failure, measuring how their hearts fill and how far they can walk. For muscle, a larger trial that isn't funded by the maker.

What this means for you

• If you have heart failure, don't swap or add anything based on this study. Ask your cardiologist about proven treatments for HFpEF, and bring the headline if you like; it's worth watching.
• If you're over 60 and want to try urolithin A for muscle, the tested dose is 500 to 1,000 mg a day for 4 months. Expect maybe more endurance, not a transformation. Judge it by something you can measure, like how many stairs you climb before resting.
• Buy a product that says how much urolithin A is in each dose. Pomegranate extract isn't the same thing.
• Keep eating pomegranates, walnuts and berries because they're good food, but don't count on them for a set dose of urolithin A.
• Walking, cycling and strength training remain the proven ways to build endurance and strength at any age. Nothing in these trials replaces them.

What's next

This starts our Heart and longevity series. The King's College team says trials in people are needed; we'll update this page if one starts. For more on staying strong as you age, see how much protein you need at your age and how to keep muscle on GLP-1 drugs.

Sources

1. Su J, Zhao Y, Coleman P, et al. Targeting PKGIα Cys42 attenuates cardiac dysfunction in heart failure with preserved ejection fraction. Sci Adv, 2026. Mice (5 to 7 per group, 7 days of urolithin A) and engineered human heart tissue from one stem-cell line (6 samples, 2 hours). Funded by the British Heart Foundation. https://doi.org/10.1126/sciadv.aec8088
2. King's College London. Pomegranates could unlock heart failure treatment. Press release, August 20, 2026. https://www.kcl.ac.uk/news/pomegranates-could-unlock-heart-failure-treatment
3. ScienceDaily. Pomegranate compound improves heart function by up to 80% in study. September 28, 2026. https://www.sciencedaily.com/releases/2026/09/260925093157.htm
4. Patrick R. How urolithin A supports mitochondrial health. FoundMyFitness, Q&A #81. Podcast. https://www.foundmyfitness.com/episodes/how-urolithin-a-supports-mitochondrial-health
5. Timeline. Pomegranate health benefits vs. Mitopure urolithin A. Company page. https://www.timeline.com/blog/pomegranate-health-benefits-vs-mitopure-urolithin-a
6. Liu S, D'Amico D, Shankland E, et al. Effect of urolithin A supplementation on muscle endurance and mitochondrial health in older adults: a randomized clinical trial. JAMA Netw Open, 2022. 66 adults aged 65 to 90, randomized, placebo-controlled, 4 months. Funded by Amazentis. https://doi.org/10.1001/jamanetworkopen.2021.44279
7. Singh A, D'Amico D, Andreux PA, et al. Urolithin A improves muscle strength, exercise performance, and biomarkers of mitochondrial health in a randomized trial in middle-aged adults. Cell Rep Med, 2022. 88 adults aged 40 to 64, randomized, placebo-controlled, 4 months. Funded by Amazentis. https://doi.org/10.1016/j.xcrm.2022.100633
8. Dao T, Nguyen TT, Gariani K, et al. Effects of urolithin A supplementation on muscle health outcomes in humans from randomized controlled trials. Front Nutr, 2026. Systematic review and meta-analysis, 5 randomized trials, 236 people. https://doi.org/10.3389/fnut.2026.1834344
9. Selma MV, Beltrán D, Luna MC, et al. Isolation of human intestinal bacteria capable of producing the bioactive metabolite isourolithin A from ellagic acid. Front Microbiol, 2017. Lab study. https://doi.org/10.3389/fmicb.2017.01521
10. Singh A, D'Amico D, Andreux PA, et al. Direct supplementation with urolithin A overcomes limitations of dietary exposure and gut microbiome variability in healthy adults to achieve consistent levels across the population. Eur J Clin Nutr, 2022. 100 adults drinking pomegranate juice, plus a randomized dosing study. Funded by Amazentis. https://doi.org/10.1038/s41430-021-00950-1