NAD+ Supplements Show Limited Human Evidence Despite Promising Animal Data

NAD+ has become one of the most discussed molecules in longevity science, with supplements like nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN) generating billions in annual sales. The premise is straightforward: NAD+ declines with age, and restoring it should slow aging. But how solid is the human evidence? This review, published in Nature Metabolism, takes a critical look at the clinical data.

Researchers from Amsterdam UMC and collaborating institutions systematically evaluated published studies on NAD+ dynamics in human tissues across aging and disease, as well as clinical trials testing NAD+ precursor supplementation. Their scope covered both the foundational question of whether NAD+ actually declines with age in humans and whether supplementation meaningfully reverses that decline.

The findings are sobering. Consistent evidence for an age-related decline in NAD+ levels in humans has been observed in only a limited number of studies. The picture is further complicated by the fact that NAD+ metabolism is highly tissue-specific — what happens in blood may not reflect what happens in muscle, liver, or brain. Most human trials have measured blood or muscle NAD+ as proxies, which may not capture the full picture.

Clinical trials of NR and NMN have shown that these supplements reliably raise blood NAD+ levels, but translating that biochemical change into meaningful health or functional outcomes has proven elusive. Improvements in metabolic markers, physical performance, or cognitive function have been inconsistent across trials.

The authors conclude that the field has moved faster than the evidence warrants. Rodent models, where NAD+ precursors show striking benefits, do not translate straightforwardly to humans. More tissue-specific, mechanistically rigorous human studies are urgently needed before broad clinical recommendations can be made.