NAD+ (nicotinamide adenine dinucleotide) is a molecule every cell needs to convert food into usable energy and to power DNA repair enzymes. Cellular NAD+ levels measurably decline with age, and restoring them, using precursor molecules like NMN (nicotinamide mononucleotide) or NR (nicotinamide riboside) that the body converts into NAD+, is one of the most heavily marketed longevity interventions available directly to consumers.
The evidence picture is a useful case study in the gap between animal and human data that this site tracks closely. In mice, NAD+ precursor supplementation has shown meaningful improvements in metabolic markers and some aging-related outcomes. In humans, trial results have been considerably more modest and inconsistent, with some studies showing measurable increases in blood NAD+ levels but limited or unclear downstream effects on the functional outcomes people actually care about.
That gap between strong preclinical signal and weak, inconsistent human confirmation is exactly the pattern this site's editorial voice is built to flag rather than paper over. NAD+ supplementation isn't disproven, but the current human evidence does not yet support the more confident claims sometimes made in consumer marketing for these products.