NMN is a direct precursor to NAD+, the coenzyme that drops with age and is required for sirtuin function and mitochondrial energy production.
Evidence: Animal data shows lifespan extension; human data shows modest improvements in muscle insulin sensitivity and physical function.
Dose: 250-500mg in the morning.
Caveats: Human longevity data is preliminary. Quality varies: many cheap products have low actual NMN content.