Vitamin B3 (niacin)

Vitamin B3 (niacin, or vitamin PP) is the precursor of NAD/NADH and NADP, coenzymes central to hundreds of metabolic reactions, notably energy production (the mitochondrial respiratory chain) and DNA repair.

The original angle (NAD, the longevity molecule): a hot topic right now: NAD+ (derived from B3) is at the heart of ageing research. Its level declines with age, which is thought to affect cellular energy and repair mechanisms.

Hence the craze for NAD precursors such as NMN (nicotinamide mononucleotide) and NR (nicotinamide riboside), sold as “anti-ageing” supplements. They do raise NAD+ in studies, with promising results in animals. But in humans, the evidence for a real anti-ageing benefit remains limited, so be wary of the marketing hype.

Synthesis from tryptophan: a particularity: the body can make a little B3 from the amino acid tryptophan (~60 mg of tryptophan → 1 mg of niacin). This is why a pure B3 deficiency is rare with sufficient protein in the diet.

Historic pellagra: severe deficiency causes pellagra (the “3 Ds”: dermatitis, diarrhoea, dementia, and even death). It struck populations that depended on untreated maize, because maize contains niacin in a non-bioavailable form. Mesoamerican civilisations had solved this empirically through nixtamalisation (treating maize with lime, which releases the niacin), a fascinating piece of ancestral knowledge that was lost when maize was exported without the technique.

Medical use: high-dose niacin has been used to modify cholesterol (lowering LDL, raising HDL), but with side effects (the “flush”) and a clinical value that is now debated.

Sources: meat, poultry, fish, peanuts, wholegrain cereals, pulses, mushrooms.