A composition comprising: a)nicotinamide riboside and b)a urolithin which is a compound of formula (I) or a salt thereof: Formula (I) wherein: A, B, C and D are each independently selected from H and OH； W, X and Y are each independently selected from H and OH； and Z is selected from H and OH. The compositions are useful as medicaments, for example for treating muscle-related pathological conditions, neurodegenerative diseases, and/or mitochondrial diseases and as dietary supplements, functional foods and beverages, and specialised nutrition or medical foods.
