Urolithin A is produced when gut bacteria ferment ellagic acid (pomegranates, walnuts, berries). About 40% of people produce it at meaningful levels; the rest can supplement. Triggers mitophagy in muscle and improves muscle endurance in older adults.
Dose: 500mg daily (Mitopure is the standardized brand).
Caveats: Pricey. Worth more in older adults than in younger trainees.