Urolithin A vs Urolithin B: What's the Difference?
Key takeaways
- Both urolithins are postbiotics—compounds your gut bacteria produce from ellagitannins found in foods like pomegranate, walnuts, and berries.
- Urolithin A has the deepest research base, including human clinical trials, and is best known for supporting mitophagy and mitochondrial quality.
- Urolithin B is much less studied; its muscle-related findings come almost entirely from cell and animal (preclinical) models, with no published human trials to date.
- Not everyone's microbiome produces meaningful amounts of either compound from food, which is one reason standardized supplements exist.
- When a label reads “standardized Urolithin A,” it refers to urolithin A specifically—not a generic urolithin blend.
If you have spent any time reading about pomegranate and longevity, you have probably seen the word urolithin. What many people do not realize is that “urolithin” is not a single molecule. It is a family of related compounds, and the two most talked-about members—urolithin A and urolithin B—have very different research stories. Understanding the difference helps you read supplement labels with clear eyes instead of marketing hype.
What exactly are urolithins?
Urolithins are not found in food directly. Instead, they are made inside your gut. Foods rich in a class of polyphenols called ellagitannins—pomegranate, walnuts, raspberries, strawberries, and some nuts—are broken down first into ellagic acid, and then your gut bacteria convert that ellagic acid into various urolithins. This makes urolithins postbiotics: end-products of microbial metabolism rather than something you eat.
The exact mix of urolithins a person produces depends heavily on the makeup of their gut microbiome. Research has shown that the ability to generate urolithin A in particular varies widely from person to person, and a meaningful share of people produce very little of it from food alone (Ryu et al., Nature Medicine, 2016 — PRECLINICAL). Urolithin B is generally considered a downstream or alternate metabolite in the same pathway, and it too depends on which bacterial species a person carries.
Urolithin A vs urolithin B at a glance
| Feature | Urolithin A | Urolithin B |
|---|---|---|
| Research depth | Extensive, including human clinical trials | Limited, mostly cell and animal studies |
| Most-studied mechanism | Mitophagy (clearing damaged mitochondria) | Muscle protein-synthesis pathways |
| Human data | Yes (safety and muscle-function trials) | No published human trials to date |
| Food precursors | Ellagitannins (pomegranate, walnuts, berries) | Ellagitannins (same sources) |
| Supplement availability | Widely available as standardized Urolithin A | Rare as a standalone ingredient |
What the research shows for urolithin A
Urolithin A is the compound that put this whole category on the map. The foundational work came from a 2016 study showing that urolithin A triggered mitophagy—the cellular process that identifies and recycles damaged mitochondria—and that this extended lifespan in the worm C. elegans and improved muscle function in rodents (Ryu et al., Nature Medicine, 2016 — PRECLINICAL). That mitophagy mechanism has since been explored in other preclinical models, including work in muscular dystrophy where urolithin A restored mitophagy and improved muscle outcomes in mice (Luan et al., Science Translational Medicine, 2021 — PRECLINICAL).
What sets urolithin A apart from urolithin B is that it has moved into people. A 2019 clinical study reported that standardized urolithin A was safe and bioavailable, and that it shifted a molecular signature associated with mitochondrial and cellular health in older adults (Andreux et al., Nature Metabolism, 2019 — HUMAN). A later randomized, placebo-controlled trial in middle-aged adults found that urolithin A supplementation was associated with improvements in muscle endurance and certain biomarkers of mitochondrial health (Singh et al., Cell Reports Medicine, 2022 — HUMAN). None of this means urolithin A treats disease; it means the human safety and structure/function research base is unusually deep for a compound in this space.
What the research shows for urolithin B
Urolithin B is a different story. The most cited work is a 2017 study identifying urolithin B as a regulator of skeletal muscle mass. In cultured muscle cells and in mice, urolithin B increased muscle protein synthesis through the Akt/mTOR pathway and reduced protein breakdown driven by the ubiquitin-proteasome system (Rodriguez et al., Journal of Cachexia, Sarcopenia and Muscle, 2017 — PRECLINICAL). That is a genuinely interesting finding, and it is a different mechanism from urolithin A's mitophagy focus—building and preserving muscle protein rather than cleaning up mitochondria.
The important caveat is that this evidence is entirely preclinical. There are no published human clinical trials demonstrating that oral urolithin B supplementation produces these effects in people, and the doses and delivery used in cell and animal studies do not translate directly to a supplement bottle. Urolithin B is an intriguing research molecule, not a proven human ingredient.
Do they come from the same place—and can your body make both?
Yes. Both urolithin A and urolithin B sit on the same metabolic pathway that begins with ellagitannins and ellagic acid. Which urolithins you end up producing, and in what amounts, depends on your particular gut bacteria. Because that microbial step is so variable, two people eating the same pomegranate can end up with very different urolithin profiles—and some people make very little urolithin A at all.
This is the core reason standardized supplements exist. A standardized SOMA Urolithin A gummies product delivers a consistent, defined dose of urolithin A directly, so the result does not depend on whether your microbiome happens to be an efficient converter. It sidesteps the “converter-status lottery” that makes relying on food alone unpredictable.
Which one should you look for in a supplement?
For most people weighing the evidence, urolithin A is the clearer choice today—not because urolithin B is “bad,” but because urolithin A is the version with human safety data and structure/function research behind it. When you see a quality label, it will specify standardized Urolithin A at a defined dose. Urolithin B, by contrast, is rarely sold on its own and has not been studied in people.
If a product is vague about which urolithin it contains, or lists only “pomegranate extract” without specifying a standardized urolithin and dose, that is a reason to look closer. The amount of actual urolithin in raw pomegranate extract is small and, again, depends on your gut to convert it.
Frequently asked questions
Is urolithin B the same as urolithin A?
No. They are chemically distinct members of the same urolithin family. Urolithin A is the most-researched and the one with human data; urolithin B has been studied mainly in cell and animal models for muscle-protein pathways.
Does urolithin A turn into urolithin B in the body?
Not in a simple one-to-one way. Both are produced from ellagic acid by gut bacteria, and which urolithins you generate depends on your microbiome—they are parallel products of the same pathway rather than one reliably converting into the other.
Can I get urolithin B from food?
Only indirectly, and only if your gut bacteria make it. Like urolithin A, urolithin B is produced from the ellagitannins in foods such as pomegranate, walnuts, and berries—but production varies a lot between individuals.
Is urolithin B safe to take?
There is not enough human data to say. Unlike standardized urolithin A, which has published human safety studies, urolithin B has not been tested in human clinical trials, so its safety and effective dose in people are not established.
Should I take a supplement with both?
Most well-studied products focus on standardized urolithin A because that is where the human evidence is. If supporting mitochondrial quality and cellular health is your goal, urolithin A is the ingredient with the research to match.
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