Vitamin B3 (Niacin)
Vitamin B3 is a family: nicotinic acid (niacin), nicotinamide (niacinamide), and the newer nicotinamide riboside and NMN. All feed into NAD⁺, the cofactor for hundreds of metabolic reactions. Different forms behave very differently at pharmacologic doses.
Daily requirements
- Men: 16 mg NE/day.
- Women: 14 mg NE/day.
- Pregnancy: 18 mg NE/day.
- Lactation: 17 mg NE/day.
- UL: 35 mg/day from supplements (based on flushing) — this does NOT apply to food or to prescription cholesterol-lowering doses under medical supervision.
NE = niacin equivalents (60 mg dietary tryptophan → 1 mg niacin).
Pellagra — the classic deficiency
"The disease of the four Ds": dermatitis (photosensitive rash on sun-exposed skin), diarrhoea, dementia, and death if untreated. Historically endemic where corn was the dietary staple (corn's niacin is bound and poorly bioavailable unless nixtamalised, as in traditional Mesoamerican preparation). Rare today outside of alcoholism, isoniazid therapy, carcinoid syndrome, and Hartnup disease.
Niacin and cholesterol
Nicotinic acid at 1,500–2,000 mg/day lowers LDL 15–20%, raises HDL 20–35%, and lowers triglycerides 20–50% — the only supplement with these effects. Yet the large AIM-HIGH (2011) and HPS2-THRIVE (2014) trials showed no reduction in cardiovascular events when niacin was added to statin therapy, and increased serious side effects. Niacin is no longer recommended for cardiovascular prevention.
The niacin flush
Nicotinic acid causes prostaglandin-mediated cutaneous vasodilation — intense warmth, redness, and tingling starting ~15 min after dose. Uncomfortable but harmless. Tolerance develops within weeks. Aspirin 325 mg 30 min before dosing blunts it. Nicotinamide and inositol hexanicotinate do not flush but also do not have the cholesterol effects.
NAD+ precursors — nicotinamide riboside and NMN
Newer supplements that raise blood NAD⁺ measurably. Marketing around anti-ageing and metabolic benefit outpaces the human trial evidence, which is small (mostly < 100 participants) and short-term. Reasonable safety profile at studied doses (250–1,000 mg/day nicotinamide riboside), but keep expectations calibrated to the actual clinical data — modest at best so far.
Food sources
- Turkey breast (3 oz): 10 mg
- Chicken breast (3 oz): 10 mg
- Tuna, canned (3 oz): 8.6 mg
- Salmon (3 oz): 8.5 mg
- Beef (3 oz): 6 mg
- Peanuts (1 oz): 4 mg
- Fortified breakfast cereal: 10–20 mg