Vitamin B3 (Niacin)Vitamin

• Blood lipid numbers, at gram dosesLikely helps

  Nicotinic acid at pharmacologic doses — roughly 100 times the RDA, taken for months to years — moves every lipid fraction in the direction cardiologists want [1].
  
  Per NIH ODS: HDL up about 20% (range 10–30%), LDL down about 17.5% (10–25%), triglycerides down about 35% (20–50%), lipoprotein(a) down about 20% (10–30%) [1].
  
  This is nicotinic acid only. Nicotinamide does not bind the receptors behind the lipid effect, so it does not do this [1].
  
  Read it as a lab-value finding, nothing more. What those numbers did not translate into is the next entry. ^[1]

• Heart attacks and strokesNot shown to help

  This is the unusual supplement claim with enough good evidence to call it a null result.
  
  A 2017 Cochrane review of 23 RCTs (39,195 people, average age 65, median 2 g/day for a median 11.5 months) found no reduction in all-cause mortality, cardiovascular mortality, heart attack or stroke [2].
  
  AIM-HIGH enrolled 3,414 patients with established cardiovascular disease on 1,500–2,000 mg/day extended-release niacin added to a statin [1].
  
  It was stopped early at 3 years: no reduction in cardiovascular events versus statin alone, despite further improvement in triglycerides, LDL and HDL — and an association with more ischemic strokes [1].
  
  HPS2-THRIVE put 25,673 patients already on a statin onto 2 g/day extended-release niacin with laropiprant for a median 4 years [1]. No significant reduction in major vascular events, and significantly more diabetes, gastrointestinal ulceration and bleeding, and skin reactions in the niacin arm [1].
  
  In the Cochrane pool, 18% of participants stopped niacin because of side effects [2].
  
  ACC/AHA cholesterol guidelines now advise against niacin as an add-on to statin therapy, on the grounds that the risk-reduction benefit does not outweigh the adverse effects [1]. ^[2]

• Niacin on its own, without a statinPossibly helps

  Sources disagree here, and we are flagging that rather than settling it.
  
  A 2019 JAMA Network Open systematic review and meta-analysis (119 trials, 35,760 participants) found niacin overall gave no cardiovascular benefit [3].
  
  Its stratified analysis, though, found niacin monotherapy — without a statin — associated with fewer acute coronary syndrome events, strokes and revascularizations [3].
  
  That signal came mainly from two trials run in the 1970s and 1980s, before statin-based care existed [3]. Every modern trial adding niacin on top of a statin found nothing, which is why current ACC/AHA guidance reads the way it does [1]. ^[3]

• Pellagra, the deficiency diseaseLikely helps

  This is what vitamin B3 is actually for. Severe niacin deficiency causes pellagra — dermatitis, diarrhea, neuropsychiatric decline — and it is fatal if left uncorrected [1].
  
  WHO's protocol is 300 mg/day of nicotinamide in divided doses for 3–4 weeks, alongside a B-complex or yeast product for the co-deficiencies that usually accompany it [1].
  
  Frank pellagra is now very rare in industrialized countries [1]. It still turns up with severe undernutrition, alcohol use disorder, malabsorptive or genetic conditions, and corn-heavy diets short on protein [1]. ^[1]

• Dietary niacin and cognitive declinePossibly helps

  The evidence here is observational, and it is about food, not supplements [4].
  
  In a 6-year prospective study of 3,718 older Chicago-area adults, higher dietary niacin intake was associated with a slower annual rate of cognitive decline [4].
  
  In a sub-analysis of 815 of them, the highest intake quintile carried roughly 70% lower relative risk of incident Alzheimer's disease than the lowest [4].
  
  Flagged conflict: a 2023 review, The Promise of Niacin in Neurology, repeats the same dietary association but frames it as needing further mechanistic and clinical work [5].
  
  No trial has tested niacin supplements against Alzheimer's disease at all. Popular write-ups overstate this one routinely [4]. ^[4]

• Pellagra is the deficiency disease, classically a triad of dermatitis, diarrhea and dementia. It is fatal if left uncorrected [1].
• A pigmented, sunburn-like rash or brown discoloration on skin exposed to sunlight, plus a bright red tongue [1].
• Digestive-tract changes causing vomiting, constipation or diarrhea [1].
• Depression, apathy, headache, fatigue and memory loss, progressing in severe cases to aggression, paranoia, hallucinations or suicidal behavior [1].
• Loss of appetite, and eventually death, where the deficiency continues [1].
• WHO's protocol for pellagra is 300 mg/day of nicotinamide in divided doses for 3–4 weeks, plus a B-complex or yeast product for the co-deficiencies that usually come with it [1].
• Highest-risk groups: undernutrition from poverty, anorexia, alcohol use disorder, AIDS, inflammatory bowel disease or liver cirrhosis [1].
• Also at risk: low riboflavin (B2), pyridoxine (B6) or iron, all of which the body needs to convert tryptophan into niacin [1].
• Also at risk: Hartnup disease, a rare inherited tryptophan-transport disorder, and carcinoid syndrome, which diverts tryptophan to serotonin instead [1].
• The most sensitive status marker is urinary excretion of two methylated metabolites. Below 5.8 µmol/day is deficient, 5.8–17.5 is low, above 17.5 is adequate [1].
• Frank pellagra is now very rare in the US, though marginal or low niacin status still occurs [1].^[1]

• Nicotinic acid, immediate releaseThe only oral form that shifts blood lipids .

  Elemental content

  Plain vitamin B3, the flushing form [1]

  Absorption

  Almost completely absorbed [1].
  
  At gram doses it activates the GPR109A/HCA2 receptor, which is exactly what produces the flush [9].

  Best for

  The only oral form that shifts blood lipids [1].
  
  Also the form that flushes hardest — more than 60% of users report mild-to-moderate flushing early on [9].

• Nicotinic acid, extended or sustained releasePrescription cholesterol management under medical supervision .

  Elemental content

  Same molecule, slowed delivery — prescription Niaspan and generics [1]

  Absorption

  Formulated specifically to reduce flushing by slowing the release rate [1].
  
  The trade-off is the liver: hepatotoxicity at gram doses is higher with extended-release formulations than with immediate-release [1].

  Best for

  Prescription cholesterol management under medical supervision [15].
  
  Given what AIM-HIGH and HPS2-THRIVE found, that indication is far narrower than it once was [1].

• Nicotinamide (niacinamide)Covering the RDA without the flush.

  Elemental content

  The amide form of B3, no flush [1]

  Absorption

  As completely absorbed as nicotinic acid [1].
  
  It does not bind the lipid-related receptors, so it neither shifts lipids nor causes flushing [1].

  Best for

  Covering the RDA without the flush. It is also WHO's chosen form for correcting pellagra, at 300 mg/day [1].

• Inositol hexanicotinate ("flush-free niacin")People trying to avoid flushing, with the caveat that less of it arrives .

  Elemental content

  A niacin–inositol complex sold as the no-flush option [1]

  Absorption

  Absorbed about 30% less on average than nicotinic acid or nicotinamide, per NIH ODS [1].
  
  So the dose on the label and the dose that gets in are not the same number.

  Best for

  People trying to avoid flushing, with the caveat that less of it arrives [1].

• Nicotinamide riboside and NMNNeither is interchangeable with a B3 supplement for meeting the RDA .

  Elemental content

  Niacin-related compounds sold separately, not labelled as niacin sources [1]

  Absorption

  Marketed and studied as NAD+ precursors rather than as vitamin B3 [1].
  
  The FDA ruled in November 2022 that NMN may not legally be sold as a dietary supplement, having first been authorized for investigation as a new drug [1].

  Best for

  Neither is interchangeable with a B3 supplement for meeting the RDA [1].

• Topical niacinamide, 2–5%Sebum and skin-barrier measures in dermatology studies .

  Elemental content

  Skincare, not nutrition — a different route entirely [6]

  Absorption

  Applied to skin, so the oral absorption figures above do not apply [6].
  
  What gets measured on skin says nothing about what an oral capsule does, or the other way round.

  Best for

  Sebum and skin-barrier measures in dermatology studies [6].
  
  See the FAQ below — this is a separate subject from oral vitamin B3 [7].

• Liver injury at gram doses

  The highest-consequence risk on this page. Nicotinic acid at 1,000–3,000 mg/day over months to years can be hepatotoxic [1].
  
  Documented effects: raised liver enzymes, hepatic dysfunction, hepatitis, and rarely acute liver failure [1].
  
  Risk runs higher with extended-release formulations than with immediate-release [1]. Naturally occurring niacin from food has not been linked to any adverse effect, liver harm included [1]. ^[1]

• Flushing

  More than 60% of niacin users get mild-to-moderate flushing, typically 20–30 minutes of burning and tingling across the face and chest per episode [9].
  
  Mechanism: nicotinic acid activates GPR109A/HCA2 on dermal Langerhans cells and macrophages, which releases prostaglandin D2 and E2 [9].
  
  A separate, non-prostaglandin route through the TRPV1 channel contributes as well [11].
  
  Tolerance builds with continued dosing because prostaglandin D2 secretion falls off, not because skin stops responding to it [9]. 325 mg of aspirin roughly 30 minutes beforehand blunts the response [9]. ^[9]

• Liver disease and active peptic ulcer

  Prescribing and interaction references list both nicotinic acid and nicotinamide as contraindicated in significant or unexplained liver disease [8].
  
  Active peptic ulcer disease is the other listed contraindication [8]. ^[8]

• Pregnancy

  The RDA of 18 mg NE/day, from food or a standard prenatal vitamin, is regarded as safe [1].
  
  Gram-level prescription niacin used for high cholesterol is not recommended during pregnancy [20].
  
  NSW Health flags preliminary Australian research on vitamin B3 in pregnancy, but urges that it be handled carefully pending further work [19]. The FAQ below has the detail. ^[19]

• Statins — myopathy and rhabdomyolysis

  Combining a statin with lipid-modifying niacin (1 g/day or more) has been reported to cause severe myopathy and rhabdomyolysis [8].
  
  The mechanism is unknown, and myopathy has been seen with either a statin alone or high-dose niacin alone [8].
  
  The risk is not evenly spread. In a double-blind RCT of simvastatin plus lipid-modifying niacin, myopathy hit 0.43% of patients of Chinese descent versus 0.03% of everyone else [8]. ^[8]

• Diabetes medication and blood glucose

  Nicotinic acid at roughly 1.5 g/day or more can raise blood glucose, by aggravating insulin resistance and increasing hepatic glucose production [1].
  
  Anyone on antidiabetes medication who takes high-dose niacin needs blood glucose monitored, and may need dose adjustments [1].
  
  HPS2-THRIVE separately found significantly more new-onset diabetes in its niacin arm [1]. ^[1]

• Warfarin and other blood thinners

  Niacin may add to the blood-thinning and bleeding-risk effect of warfarin and other anticoagulant or antiplatelet drugs, per WebMD's drug monograph [12]. ^[12]

• Alcohol

  Alcohol taken alongside niacin can worsen flushing and itching [12].
  
  It may also raise the risk of liver damage, which stacks on top of niacin's own liver signal at gram doses [12]. ^[12]

• Isoniazid and pyrazinamide (TB drugs)

  Both are structural analogs of niacin, and both interrupt the conversion of tryptophan into niacin [1].
  
  They can bring on pellagra in patients receiving tuberculosis therapy unless niacin intake goes up [1]. ^[1]

Niacin is spread widely through the food supply, so most people clear the RDA without trying [1].

Animal foods — poultry, beef, fish — typically give 5–10 mg per serving, mostly as NAD/NADP, which is highly bioavailable [1].

Plant foods — nuts, legumes, grains — typically give 2–5 mg per serving, mostly as nicotinic acid [1].

Per NIH ODS, per serving: beef liver, pan fried, 3 oz — 14.9 mg (93% DV). Grilled chicken breast, 3 oz — 10.3 mg (64% DV).

Roasted turkey breast, 3 oz — 10 mg (63% DV). Canned light tuna in water, drained, 3 oz — 8.6 mg (54% DV).

Cooked sockeye salmon, 3 oz — 8.6 mg (54% DV). Cooked brown rice, 1 cup — 5.2 mg (33% DV).

Dry-roasted peanuts, 1 oz — 4.2 mg (26% DV). One medium baked russet potato — 2.3 mg (14% DV).

The catch is in grains. Niacin bound to polysaccharides and glycopeptides in some grain products is only about 30% bioavailable, unless the grain is alkali-processed — nixtamalized corn, for instance [1].

Niacin added to fortified or enriched foods is in free, highly bioavailable form [1]. Protein counts too: 60 mg of tryptophan converts to 1 mg NE, so 3 oz of turkey breast (~180 mg tryptophan) is worth roughly 3 mg NE on its own [1].

Timing only matters at pharmacologic doses. For ordinary multivitamin-level niacin there is nothing to schedule [15].

Prescription extended-release niacin (Niaspan) is meant to be taken at bedtime after a low-fat snack — partly to reduce flushing, partly so any flush happens while you are asleep [15].

Cleveland Clinic's patient guidance says the same, for the same two reasons [16].

Aspirin or ibuprofen about 30 minutes before the dose is the standard way to blunt flushing [15].

Avoid alcohol, hot drinks and spicy food around dosing time — all three make flushing worse [15].

Dose escalation is deliberately slow: roughly 0.5 g/day up to 1.0 g/day over about 8 weeks, as flushing fades with tolerance [9].

If doses have been missed for a stretch, clinical guidance is to check with the prescriber before restarting, rather than resuming at the old maintenance dose [15].