NAD+Nicotinamide adenine dinucleotide

NAD+ is a coenzyme derived from vitamin B3 that shuttles electrons in metabolism, cycling between its oxidised form NAD+ and reduced form NADH. It is indispensable to glycolysis, the Krebs cycle and oxidative phosphorylation, and it is also consumed by the sirtuin and PARP enzymes involved in DNA repair.

It matters because tissue NAD+ levels fall with age, and restoring them in mice improves several markers of ageing — the observation that launched the NMN and NR supplement market.

In practice the human evidence lags well behind the enthusiasm. Trials of NR and NMN show these compounds do raise blood NAD+ levels, but have so far failed to demonstrate the meaningful functional or healthspan benefits the marketing implies. Exercise itself raises NAD+ in muscle, and remains the intervention with actual outcome data behind it.