NMN (Nicotinamide Mononucleotide)

NMN is the most discussed longevity supplement in academic circles and the most controversial on this list. It is a precursor to NAD+, a molecule that declines approximately 50% between age 20 and 50 and plays a central role in DNA repair, mitochondrial function, and cellular senescence. Animal studies are consistently impressive. Human trials have been mixed but improving: a 2023 double-blind RCT published in Nature Aging found 300mg/day NMN improved muscle insulin sensitivity and physical performance in overweight adults. The honest assessment: the human evidence is still thin relative to the theoretical mechanism. Price is high ($60-100/month for quality brands). The 2025 Longevity Research Consortium grades it B for human evidence — promising but not yet A-tier. Taking it costs money; not taking it carries the risk of missing a genuine discovery.