Niacin: Benefits, Dosage, and Safety

What niacin is

Niacin is one of the water-soluble B vitamins. It is the generic name for nicotinic acid, nicotinamide (niacinamide), and related derivatives such as nicotinamide riboside. All tissues convert absorbed niacin into its main metabolically active form, the coenzyme nicotinamide adenine dinucleotide (NAD), and into nicotinamide adenine dinucleotide phosphate (NADP). It is naturally present in many foods, added to some fortified foods, and available as a dietary supplement. The amino acid tryptophan can also be converted to NAD in the body, so it is considered a dietary source of niacin (about 60 mg tryptophan yields 1 mg niacin).

What it does

• Serves as the precursor of NAD, a coenzyme required by more than 400 enzymes, more than for any other vitamin-derived coenzyme
• Supports catabolic redox reactions that transfer energy from carbohydrates, fats, and proteins to ATP, the cell's primary energy currency
• As NADP, enables anabolic reactions such as the synthesis of cholesterol and fatty acids
• Contributes to maintaining cellular antioxidant function
• Participates in maintenance of genome integrity, control of gene expression, and cellular communication

How much niacin per day

These are population reference values from the NIH and the Dietary Reference Intakes. They are targets for healthy people, not personal prescriptions. The last column is the Tolerable Upper Intake Level, the most you should get from all sources combined.

Deficiency and who is at risk

Severe niacin deficiency causes pellagra, characterized by a pigmented rash or brown discoloration on sun-exposed skin that develops a roughened, sunburned-like appearance. Pellagra can also cause a bright red tongue and digestive changes leading to vomiting, constipation, or diarrhea. Neurological symptoms can include depression, apathy, headache, fatigue, and memory loss that may progress to aggressive, paranoid, and suicidal behaviors and to auditory and visual hallucinations. As it progresses, anorexia develops and the disease can eventually be fatal. Pellagra is uncommon in industrialized populations and is mostly limited to people in poverty who eat very limited diets low in niacin and protein.

Who may need more

• People who are undernourished due to poverty, anorexia, alcohol use disorder, AIDS, inflammatory bowel disease, or liver cirrhosis
• People with inadequate riboflavin, vitamin B6, or iron intakes
• People with Hartnup disease
• People with carcinoid syndrome
• People being treated for tuberculosis with isoniazid, which can interfere with niacin production and increase pellagra risk

Food sources

Beef liver (14.9 mg per 3 oz), chicken breast (10.3 mg per 3 oz), marinara sauce (10.3 mg per cup), turkey breast (10.0 mg per 3 oz), sockeye salmon (8.6 mg per 3 oz), canned light tuna (8.6 mg per 3 oz), pork tenderloin (6.3 mg per 3 oz), 90% lean ground beef (5.8 mg per 3 oz), brown rice (5.2 mg per cup), dry roasted peanuts (4.2 mg per oz), fortified breakfast cereals (about 4.0 mg per serving), and enriched breads and cereals. Animal foods provide highly bioavailable NAD and NADP; niacin in some grains is largely bound and only about 30% bioavailable, while niacin added to enriched and fortified foods is in free, highly bioavailable form.

Forms and absorption

Nicotinic acid and nicotinamide are the two most common supplement forms; both are almost completely absorbed. Nicotinic acid in amounts beyond nutritional needs causes skin flushing, so some products are made as prolonged, sustained, extended, or timed release to reduce this. Nicotinamide does not produce flushing due to its slightly different chemical structure. Inositol hexanicotinate is marketed as flush free; its absorption varies widely but averages about 30% lower than nicotinic acid or nicotinamide. Nicotinamide riboside and nicotinamide mononucleotide (NMN) are related compounds sold as supplements but not labeled as niacin sources; FDA ruled in November 2022 that NMN may not be legally marketed as a dietary supplement. Prescription extended-release nicotinic acid (Niaspan, generic niacin ER) provides 500-1,000 mg to treat high cholesterol.

Safety, excess and interactions

Too much

No adverse effects have been reported from naturally occurring niacin in foods. Supplemental nicotinic acid at roughly 30 to 50 mg or more typically causes flushing (reddening of the skin on the face, arms, and chest from vasodilation) with burning, tingling, and itching; this is considered an unpleasant rather than toxic effect and can be accompanied by headache, rash, dizziness, or lowered blood pressure. Pharmacologic doses of 1,000 to 3,000 mg/day nicotinic acid can cause more serious effects: hypotension severe enough to increase fall risk, fatigue, impaired glucose tolerance and insulin resistance, gastrointestinal effects (nausea, heartburn, abdominal pain), and ocular effects (blurred vision, macular edema). High doses over months or years can be hepatotoxic (elevated liver enzymes, hepatic dysfunction, hepatitis, acute liver failure), more likely with extended-release forms. Nicotinamide does not cause flushing and has fewer effects, but nausea, vomiting, and signs of liver toxicity can occur at intakes of 3,000 mg/day.

Interactions to know

• Isoniazid and pyrazinamide (in Rifater), used for tuberculosis, are structural analogs of niacin that interrupt niacin production from tryptophan by competing with a vitamin B6-dependent enzyme; isoniazid can also interfere with niacin's conversion to NAD, and pellagra can occur in treated patients unless niacin intake is increased
• Antidiabetes medications: large doses of nicotinic acid (1.5 g/day or more) can raise blood glucose by causing or aggravating insulin resistance and increasing hepatic glucose production, so people on antidiabetes drugs taking high-dose nicotinic acid may need blood glucose monitoring and dose adjustments

How status is measured

Blood niacin levels are not reliable indicators of status. The most sensitive, reliable measure is urinary excretion of the two major methylated metabolites, N1-methyl-nicotinamide and N1-methyl-2-pyridone-5-carboxamide: adult excretion above 17.5 micromol/day reflects adequate status, 5.8 to 17.5 micromol/day reflects low status, and below 5.8 micromol/day indicates deficiency. Supporting measures include a niacin number (whole-blood NAD:NADP ratio x 100) below 130 suggesting deficiency, and a niacin index (erythrocyte NAD:NADP ratio) below 1 indicating risk. No functional biochemical test of total body niacin stores is available.

Regulated as a dietary supplement ingredient under the Dietary Supplement Health and Education Act; not FDA-approved to treat, cure, or prevent disease. The FDA Daily Value (DV) for niacin is 16 mg for adults and children 4 years and older. Prescription extended-release nicotinic acid (Niaspan and generics) is an FDA-regulated medicine for high cholesterol. FDA ruled in November 2022 that nicotinamide mononucleotide (NMN) may not be legally marketed as a dietary supplement.

What the evidence supports

We grade the strength of evidence behind each common reason people take niacin, mirroring how the NIH describes it.