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Vitamin B3 (Niacin) — The Complete Supplement Guide

One vitamin, several very different forms — nicotinic acid, nicotinamide and the NAD precursors. What each does, and the flushing and liver limits.

Reviewed by Bodil Isaksson, Licensed Biomedical Scientist (Sweden)Last reviewed July 2026Supplement guide

SupplementsVitaminsB3 NiacinWater-soluble

The one B vitamin with a split personality: its two forms — nicotinic acid and nicotinamide — behave so differently that they are almost separate supplements. For the short dietary version, see the Vitamins page.

Read first. High-dose nicotinic acid causes flushing and, at gram doses, liver strain — historically a prescription cholesterol treatment, not a casual supplement. Nicotinamide is gentler. Information, not a prescription.

Key takeaways

  • The two forms differ: nicotinic acid flushes and can lower cholesterol; nicotinamide does neither.
  • Adults need ≈ 14–16 mg NE/day.
  • Supplemental upper limit 35 mg/day (nicotinic acid); high therapeutic doses are medical.

Function

Niacin's job is to make the NAD/NADP coenzymes:

  • Energy metabolism: NAD carries electrons in the reactions that release energy from food in every cell.
  • Biosynthesis & antioxidant: NADP powers the making of fats and the regeneration of antioxidants.
  • DNA repair & signalling: NAD is used by repair and signalling enzymes (sirtuins, PARPs) linked to cell health and ageing.
  • Skin, nerves & digestion: needed to keep skin, the nervous system and the gut lining healthy.

Different forms — and which to choose

Nicotinic acid (niacin)Causes a warm flush; the only form that lowers cholesterol at gram doses (prescription, specialist).
Nicotinamide (niacinamide)No flush, no cholesterol effect; the gentle everyday form, studied for skin.
"No-flush" (inositol hexanicotinate)Marketed as flush-free niacin but releases little active niacin — largely ineffective.
NR / NMN (NAD precursors)Newer NAD-boosting supplements marketed for ageing/energy — early evidence, expensive.

Absorption in the body

How muchWell absorbed. The body can also make niacin from the amino acid tryptophan (~60 mg tryptophan → 1 mg niacin).
NoteIntake is expressed as "niacin equivalents" (NE) to include the tryptophan contribution.

Deficiency symptoms

SymptomsPellagra — the "three D's": dermatitis (sun-exposed skin), diarrhoea and dementia; untreated it can be fatal.
Who's at riskVery poor diets, chronic alcohol use, and malabsorption; rare where diets are varied.

Recommended intake

Adults ≈ 14–16 mg NE/day

Reference intakes (niacin equivalents):

  • Adults: ~14 mg ♀ / 16 mg ♂ NE per day

Best sources: meat, poultry, fish, peanuts, wholegrains, plus what the body makes from protein.12

Therapeutic use

CholesterolPrescription high-dose nicotinic acid (1–3 g) was used for blood lipids — specialist-only and now largely replaced by safer drugs.
SkinNicotinamide 500 mg twice daily reduced new non-melanoma skin cancers in high-risk people (ONTRAC trial); also used topically for acne/rosacea.

Therapeutic doses

Everyday small; therapeutic = medical
EverydayDiet covers needs; a multivitamin dose is small.
High doseGram-level nicotinic acid is a medical decision with monitoring.

Toxicity & upper limit

UL: 35 mg/day supplemental (nicotinic acid)
Upper limit35 mg/day of supplemental nicotinic acid (the flushing threshold).1
FlushNicotinic acid causes skin flushing and itching; gram doses can strain the liver and raise blood sugar.
NicotinamideBetter tolerated, but very high doses also stress the liver.

Bottom line: niacin comes readily from protein-rich foods. The forms matter: use nicotinamide for gentle everyday needs, treat high-dose nicotinic acid (cholesterol) as a supervised medicine, and regard NR/NMN "anti-ageing" NAD boosters as promising but unproven.

← All supplementsShort dietary version

References

Reference and upper-limit values are general adult figures from official bodies; individual needs vary. Therapeutic doses describe clinical/research use, not prescriptions.

  1. US NIH Office of Dietary Supplements. Niacin — Health Professional Fact Sheet (function, forms, intakes, food sources, deficiency, therapeutic uses, upper limit, interactions). ods.od.nih.gov
  2. EFSA. Dietary Reference Values & Tolerable Upper Intake Levels for vitamins (European reference intakes and ULs). efsa.europa.eu

This article summarizes nutrition science from official health authorities and peer-reviewed sources for education. It is not a substitute for individual medical advice, and the doses given are not prescriptions — always consult a professional before therapeutic supplement use, in pregnancy, or alongside medication.

✓
Bodil Isaksson, Licensed Biomedical Scientist (Sweden)

At Food Health Lab we explain what the science says in plain language, and we cite our sources so you can check for yourself.

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