Urolithin A Explained Simply

1. What It Is About

Urolithin A is not eaten directly. It is only formed in the intestine when certain bacteria convert components of pomegranates, walnuts, raspberries and strawberries. These components are called ellagitannins. Whether and how much urolithin A is formed varies greatly from person to person. Some people form none at all, others form plenty. This depends on which bacteria live in the intestine, for example Gordonibacter urolithinfaciens. Experts therefore distinguish three groups, which they call metabotypes: Metabotype 0 forms no urolithins, Metabotype A forms urolithin A and iso-urolithin A, Metabotype B forms only urolithin B. This difference is important because it explains why studies produce different results in different people. So far, 516 papers have been evaluated, including 12 controlled studies in humans, 69 observational studies and 83 animal experiments. The focus of investigation has been mainly on the intestine, muscles and inflammatory markers. A controlled study works like this: One part of the participants receives the substance, another receives a placebo without active ingredient, and no one knows in advance who receives what.

2. What Studies Show

The effect on muscles and endurance is the best investigated. In a controlled study 1 66 older people between 65 and 90 years of age took urolithin A or a placebo daily for four months. The urolithin A group walked further in the six-minute walk test and sustained a load on the arm and leg muscles for longer. A laboratory value for cellular energy production remained unchanged, however. These are indications, but not yet confirmed, because the study was short and did not differentiate by metabotype. An overview paper 7 pooled three controlled studies with a total of 174 participants between 24 and 72 years of age. Here too there were indications of greater muscle strength and better physical performance. The results diverged, however, and long-term observations are still outstanding. A study 6 followed 42 well-trained long-distance runners for four weeks. After strenuous downhill runs, inflammatory markers and a marker of muscle strain in the blood were slightly lower in the urolithin A group. The difference was too small to be certain, however. Endurance and running economy did not improve. In 32 healthy adults a study 4 over four weeks altered the composition of intestinal bacteria. Several bacterial species became more frequent and more urolithin could be detected in the urine. A pomegranate extract was tested, however, not the pure substance. Whether the changes were due to urolithin A is therefore only a hypothesis so far. In an evaluation of the MaPLE study 2 an eight-week polyphenol-rich diet was examined for its effect on intestinal permeability in 51 older people. A protein in the blood associated with this permeability was measured. In people with metabotype B this value fell more sharply than in metabotype A. What this means for everyday life has not been investigated. In mice with a hereditary muscle disease urolithin A in an animal study 8 prolonged life and improved muscle regeneration. Such animal findings are an early indication. Whether they apply to humans remains open.

3. What Remains Unclear

Some controlled human studies last four to twelve weeks and include few participants. How longer intake affects outcomes is therefore open. In a small study of 10 people with heart failure 5 heart values did not change, only one cholesterol value rose. In 20 strength athletes 3 inflammatory markers remained unchanged over eight weeks. Whether the observed shifts in intestinal bacteria promote urolithin A production is suspected but not shown. It has also hardly been compared whether foods containing ellagitannins achieve the same effect as a preparation with the pure substance. Many studies do not classify their participants by metabotype, so it remains unclear who actually benefits from supplementation. How the laboratory changes relate to well-being is therefore a question for further studies.

4. What This Means in Everyday Life

Urolithin A is formed in the intestine when ellagitannin-rich foods are eaten. How much is formed varies from person to person and cannot be read from a feeling. The studies so far point to small advantages in muscle strength and endurance, especially in older people and athletes. They say nothing, however, about whether this continues over months or years. It is also not clear whether intake via foods or via a preparation has the same effect. Anyone interested in the substance will find in the cited papers the values that were measured there. The next step would be to clarify how longer intake affects the different metabotypes and whether the measured laboratory changes mean something for people’s everyday lives.

All Details with Study Numbers and Sources: detailed page on Urolithin A. For Children: Urolithin A for Children.