Category: biosynthesis
NAD+ / NADP+ are the major cellular hydride acceptors — used by hundreds of dehydrogenases plus sirtuins (NAD+-consuming deacetylases) plus PARPs (NAD+-consuming DNA repair). Sources: (1) De novo from tryptophan via the kynurenine pathway (see tryptophan_metabolism) — quinolinic acid → NAD+ via QPRT. (2) Preformed from dietary niacin (nicotinic acid / nicotinamide / nicotinamide riboside) via the Preiss-Handler pathway. ~60 mg dietary tryptophan = 1 mg niacin equivalent. Pellagra (niacin deficiency) presents as the 4 D's: dermatitis, diarrhea, dementia, death — historically endemic in corn-dependent populations because corn niacin is bound and bioavailability is low. NAD+ supplementation (NR, NMN, NAD+ precursors) is heavily promoted for longevity but rigorous evidence remains thin.