Urolithin A: the molecule your body is supposed to make but probably doesn't

There's a compound that your body was designed to produce every time you eat pomegranates, walnuts, or raspberries. It plays a critical role in keeping your muscle cells healthy as you age, and there's roughly a 60% chance your body isn't making enough of it.

The compound is called urolithin A, and it's one of the most exciting developments in aging research in the last decade. Not because it's new to science, but because we're finally understanding why most people are missing out on it and what happens when you give it back to them.

Your cells have power plants, and they're getting old

Every cell in your body contains mitochondria, small structures that convert food into usable energy. Think of them as tiny power plants. When you were younger, these power plants ran efficiently, producing the energy your muscles needed to work, recover, and grow. But as you age, mitochondria accumulate damage and become less efficient, producing less energy and more waste. Your muscles feel the difference in the form of less endurance, slower recovery, and easier fatigue.

Mitochondrial decline is one of the most well-documented hallmarks of aging, and it's directly connected to sarcopenia, the progressive loss of muscle mass and strength that affects up to half of adults over 80. Your muscles aren't just shrinking because you're less active; they're losing power at the cellular level because the engines inside them are wearing out.

The cleanup crew your body is supposed to have

Your body actually has a built-in system for dealing with damaged mitochondria. It's called mitophagy, which translates roughly to "eating your own mitochondria," and despite the unsettling name, it's one of the most important maintenance processes in your biology. Mitophagy identifies mitochondria that are broken or inefficient, breaks them down, and clears space for fresh, healthy ones to take their place.

When mitophagy is working well, your cells continuously renew their energy supply, swapping out old mitochondria for fresh ones the way a well-run factory rotates its equipment. But this process slows down as you age, and when it does, damaged mitochondria start to pile up, dragging down the performance of the entire cell.

Urolithin A is a natural activator of mitophagy, essentially the signal that tells your body to start the cleanup process. And this is where the story gets interesting.

The pomegranate problem

Urolithin A isn't actually found in food. You can't eat it directly. Instead, your body is supposed to produce it when you consume foods rich in compounds called ellagitannins, which are abundant in pomegranates, walnuts, strawberries, and raspberries. Your gut bacteria break down those ellagitannins through a series of metabolic steps, and the final product of that process is urolithin A.

The problem is that this conversion depends entirely on having the right mix of gut bacteria, and most people don't. Research has found that only about 40% of people produce significant levels of urolithin A after consuming pomegranate juice. The rest have gut microbiomes that either can't complete the conversion or produce only trace amounts. Your age, diet history, antibiotic use, and overall gut health all influence whether you're in the lucky minority or the majority that's missing out.

This means you could drink pomegranate juice every morning for a year and still not get a meaningful dose of urolithin A. The bottleneck isn't your diet, it's your microbiome, and for roughly 60% of the population, that bottleneck isn't going away on its own.

What happens when you supplement it directly

This is where the clinical research comes in. A randomized, double-blind, placebo-controlled trial published in JAMA Network Open in 2022 tested what happens when you bypass the gut bacteria problem entirely and give older adults urolithin A directly.

The study enrolled 66 adults between the ages of 65 and 90. Half received 1,000 milligrams of urolithin A daily for four months. The other half received a placebo. Researchers measured muscle endurance by counting how many times participants could contract specific muscles before reaching fatigue, testing both a hand muscle and a leg muscle at baseline, two months, and four months.

The results were striking: the urolithin A group showed a 26% improvement in hand muscle endurance and a 17% improvement in leg muscle endurance compared to placebo, with most of those gains appearing within the first two months. The placebo group, meanwhile, stayed essentially flat, and their leg endurance actually declined slightly by month four.

Beyond endurance, the researchers found that urolithin A reduced plasma levels of C-reactive protein, a key marker of systemic inflammation. It also lowered levels of acylcarnitines and ceramides, which are biomarkers associated with mitochondrial dysfunction. In plain language: it wasn't just making muscles last longer, it was improving the underlying cellular health that drives muscle performance.

The study also confirmed that urolithin A was safe and well-tolerated, with no significant difference in adverse events between the supplement and placebo groups. The FDA had already listed urolithin A as Generally Recognized as Safe in 2018 at doses between 250 and 1,000 milligrams per day.

What the study didn't show (and why that's okay)

In the interest of being straightforward: the trial did not find a statistically significant improvement in the six-minute walk test or in maximum ATP production compared to placebo. Walking distance improved in both groups (likely due to the familiarity effect of repeated testing), and the difference between them wasn't large enough to reach significance.

This doesn't undermine the findings. It suggests that urolithin A's primary benefit is at the cellular and muscular endurance level, improving how long your muscles can sustain effort rather than dramatically increasing peak power output in the short term. For the daily life of someone over 65, endurance is arguably more relevant anyway, since carrying groceries from the car, walking through an airport, and keeping up with grandkids at the park are all sustained-effort activities, not sprints.

The researchers noted that longer supplementation periods may be needed to see improvements in broader functional measures, and several follow-up studies are now underway.

Why this matters for your daily routine

Urolithin A isn't a miracle molecule and it doesn't replace exercise, protein, or any of the other fundamentals of healthy aging. What it does is address a specific biological bottleneck that most people over 50 are experiencing whether they know it or not, which is the gradual failure of your cells to clean house and renew their own energy supply.

When your mitochondria work better, your muscles produce more energy, sustain effort longer, and recover faster. That translates directly into the things that matter in daily life: being able to do more before you feel tired, bouncing back faster after a hard day, and maintaining the physical resilience that keeps you independent.

We include 500 milligrams of urolithin A in every scoop of Stronghold because the science supports it and because it fills a gap that most people's bodies can't fill on their own. Paired with protein for muscle building, creatine for muscle fueling, and HMB for muscle protection, urolithin A handles the cellular renewal layer, making sure the power plants inside your muscles are actually equipped to use everything else you're giving them.

Your body was designed to make urolithin A. Stronghold makes sure you actually get it.

Sources: Liu et al., JAMA Network Open, January 2022 (PMC8777576). Singh et al., Nature Metabolism, 2019 (urolithin A mechanism and mitophagy activation). FDA GRAS notification for urolithin A, GRN No. 791, 2018. Ryu et al., Nature Medicine, 2016 (urolithin A and mitochondrial function in aging).