Vitamin B3 (Niacin)
One vitamin, two forms, two very different ceilings. Only one of them makes you flush.
Vitamin B3 covers two compounds that behave differently once you go past dietary amounts. Nicotinic acid causes the flush, a prostaglandin-driven skin reaction that is harmless and deeply unpleasant, and the NHS puts the amount unlikely to cause harm at 17mg a day of supplemental nicotinic acid. Nicotinamide does not flush, and the same NHS guidance allows 500mg a day. Adults need roughly 16.5mg a day if male and 13.2mg if female, which most diets cover, so almost everyone taking a B3 supplement is doing it for something other than deficiency. That something used to be cholesterol: high-dose nicotinic acid does move lipid numbers, but the 25,000-patient HPS2-THRIVE trial in 2014 found no reduction in major vascular events when it was added to a statin, and did find more side effects. Nicotinamide riboside and NMN are also B3 forms, and they are a different argument entirely.
Reference values
Daily reference values from official nutrition authorities. These are population reference figures, not personal recommendations.
| RDA | Upper limit | Source |
|---|---|---|
| 17 mg | 10 mg | UK SACN DRVs (1991) — 17mg NE/day; EFSA UL 10mg/day nicotinic acid (flushing threshold), used as the stored ceiling since it is the form that causes harm — nicotinamide has no established UL. Applying the lower, more conservative figure protects users on the nicotinic acid form; a single ul_amount column can't hold two per-form ceilings (see #715). |
Forms and bioavailability
Not all forms are absorbed equally. The form on your supplement label affects how much your body can actually use.
| Form | Absorption | With food | Timing | Evidence |
|---|---|---|---|---|
| nicotinic acid (niacin) | Typical | With food | Either | Strong |
| niacinamide (nicotinamide) | Typical | Either | Either | Strong |
| inositol hexanicotinate | Typical | With food | Either | Possible |
| nicotinamide riboside (NR) | Higher | Either | Either | Likely |
| NMN (nicotinamide mononucleotide) | Higher | Either | Either | Possible |
Stack Almanac tracks which B3 form you are on, because a 500mg nicotinamide capsule and a 500mg nicotinic acid capsule are the same number against two ceilings that differ by a factor of thirty.
Track your Vitamin B3 (Niacin) in Stack Almanac
Reference values are adult-general RDAs from UK. Individual needs may vary. This page is for informational purposes only and is not a substitute for professional medical advice.