The First Human Trial of Urolithin A: Is It Safe?

This is the foundational study that put urolithin A on the map as a human-relevant compound, rather than just a promising finding in worms and old mice. Sixty elderly, sedentary but otherwise healthy adults were split into four groups, each receiving either placebo or a 250mg, 500mg or 1,000mg daily dose of urolithin A for 28 days. The primary aim was simply safety, and urolithin A cleared that bar at every dose tested, showing up reliably in the bloodstream after oral consumption. As a secondary outcome, the two higher doses altered plasma markers of fat metabolism and, more notably, changed the activity of mitochondrial genes in skeletal muscle, an early molecular signature consistent with improved mitochondrial health. This was never designed to prove functional benefits like strength or endurance gains, only to establish that urolithin A is safe and biologically active in people, which it accomplished. Every later human urolithin A trial, including the 2025 immune-aging study above, builds directly on this one.