Vitamin B3 – Niacin

Vitamin B3 — also called niacin — is a water-soluble B vitamin and the building block of NAD+ and NADP+, two coenzymes involved in more enzyme reactions than any other vitamin-derived molecule in the body — over 400 of them, covering energy production, DNA repair, gene regulation, and cell signaling. Studies suggest NAD+ levels fall with age in several tissues, which has made vitamin B3 and its relatives a major focus of longevity research — giving it a relevance well beyond energy metabolism and cholesterol management.

Vitamin B3 – Key Mechanisms

NAD+ and NADP+ — the core of vitamin B3’s function: the body converts vitamin B3 into NAD+ and NADP+, coenzymes with distinct but complementary roles:

• NAD+ as an electron carrier: in the electron transport chain, NADH (the reduced form of NAD+) donates electrons to Complex I, driving ATP production. Glucose, fat, and amino acids broken down for energy pass most of their electrons through NAD+, so it sits at the center of ATP production.
• NAD+ as a signaling molecule: beyond energy production, NAD+ is used up — not just recycled — by three major enzyme families:
  • Sirtuins (SIRT1–7): enzymes that help regulate gene expression, DNA repair, mitochondrial function, circadian rhythm, and metabolism. They need NAD+ to work, so NAD+ availability influences how well these regulatory systems function.
  • PARPs (poly-ADP-ribose polymerases): key DNA-repair enzymes. When DNA is damaged, PARPs consume NAD+ to build chains that signal the repair machinery. UV exposure, oxidative stress, and other DNA damage all trigger PARP activity.
  • CD38: an enzyme involved in calcium signaling and immune function that breaks down NAD+, and whose activity rises with age and inflammation.
• NADP+ in building and antioxidant defense: NADPH (the reduced form of NADP+) supplies the electrons for making fatty acids and cholesterol, and for recycling glutathione and thioredoxin — two of the body’s main antioxidant systems.

NAD+ and aging: NAD+ levels appear to decline with age in several tissues, partly because NAD+-consuming enzymes such as CD38 become more active. In animal studies, falling NAD+ is linked to reduced mitochondrial function and weaker DNA repair, and restoring it has produced striking results. Whether boosting NAD+ slows aging in humans is still unproven — it’s one of the most active areas of longevity research, but human trials so far have shown modest effects at best.

The niacin flush: the flushing caused by high doses of nicotinic acid — redness, warmth, and itching, starting in the face — happens when nicotinic acid activates a receptor (GPR109A) on immune and skin cells, which release prostaglandins that widen the blood vessels in the skin. The flush is harmless but can be intense. It’s specific to the nicotinic acid form of vitamin B3 — niacinamide doesn’t cause it.

Making niacin from tryptophan: the body can make vitamin B3 from the amino acid tryptophan — about 60mg of tryptophan produces 1mg of niacin. This conversion needs vitamin B2, vitamin B6, and iron. That’s why vitamin B3 requirements are given in niacin equivalents (NE), which count both the niacin in food and the niacin made from tryptophan.

Vitamin B3 – RDA (Recommended Dietary Allowance)

NE = niacin equivalents, counting both dietary niacin and niacin made from tryptophan (60mg tryptophan = 1mg NE). * Adequate Intake (AI) for infants; for 0–6 months, preformed niacin. Source: US National Academies, via the NIH Office of Dietary Supplements. The daily value used on food labels is 16mg.

Vitamin B3 – ODA (Optimal Daily Allowance)

Meet the RDA — 14–16mg NE a day for adults — which most people easily get from food, since protein foods supply both niacin and tryptophan. There’s no good evidence that higher intakes improve health for most people, and supplemental niacin above the 35mg upper limit can cause flushing (as nicotinic acid). Higher-dose uses — nicotinic acid for blood lipids, nicotinamide for skin cancer prevention in high-risk people, and NAD+ precursors such as NR and NMN — are separate, therapeutic or experimental uses, covered below, and are best discussed with a doctor.

Vitamin B3 is Found In (per 100g)

* Value from USDA’s SR Legacy data, where the Foundation Foods entry doesn’t include it. Figures are preformed niacin only; protein-rich foods provide extra niacin equivalents from their tryptophan.

Fish, meat, and poultry are the most concentrated vitamin B3 sources, and because they’re also rich in tryptophan, they provide even more niacin equivalents than the table shows. Peanuts and sunflower seeds are standout plant sources, and mushrooms, whole grains, and fortified foods also contribute.

One important nuance: much of the niacin in corn is bound in a form the human gut can’t easily absorb, and corn is also low in tryptophan. Traditional Mexican and Central American preparation — nixtamalization, cooking corn in an alkaline solution such as lime water — releases the bound niacin. Populations in Europe and the southern United States that adopted corn as a staple without this preparation suffered widespread pellagra.

Vitamin B3 Helps With

• Producing ATP through the electron transport chain — NADH feeds Complex I
• Gene regulation and cellular maintenance through sirtuins
• Repairing DNA damage through PARP enzymes
• Making fatty acids and cholesterol (via NADPH)
• Antioxidant defense through the glutathione and thioredoxin systems
• Blood lipids — at high doses, nicotinic acid raises HDL and lowers triglycerides and Lp(a), though this hasn’t translated into fewer heart attacks in modern trials (see below)
• Healthy skin and mucous membranes — and, at high doses, nicotinamide has reduced new non-melanoma skin cancers in people with a history of them
• Normal nervous system and brain function

Vitamin B3 – for Athletes and Active People

Vitamin B3’s central role in energy production makes adequate intake essential for athletes — though, as with other B vitamins, getting enough is what matters, not taking extra.

NAD+ turnover during exercise: hard training runs large amounts of NAD+ and NADH through energy metabolism, and the oxidative stress of intense exercise can activate NAD+-consuming repair enzymes. Athletes’ diets — typically high in protein and calories — usually supply plenty of niacin and tryptophan to cover this.

Mitochondrial adaptation: sirtuins, which need NAD+, help regulate PGC-1α — a master regulator of new mitochondria. Exercise is the main driver of this adaptation, and adequate vitamin B3 supports the pathways involved. Exercise itself also raises NAD+ levels in muscle.

NR and NMN for athletes: interest in NAD+ precursors for longevity has spread to sport. Human trials show that NR and NMN reliably raise NAD+ levels in the blood, but effects on muscle NAD+ have been inconsistent, and performance studies are few, small, and mixed. For now, there’s no strong evidence they improve athletic performance or recovery.

Niacinamide: if an athlete wants to supplement, niacinamide — at modest doses, such as in a multivitamin or B-complex — is the simplest way to cover needs without the flushing or blood-lipid effects of nicotinic acid.

One caution: high-dose nicotinic acid temporarily suppresses the release of fat from fat stores (one of the ways it lowers triglycerides). Taken around training, this can reduce fat availability during exercise and increase reliance on glycogen, which may impair endurance. This applies to high-dose nicotinic acid, not niacinamide or NR and NMN.

Vitamin B3 – Deficiency

Deficiency risk is higher in:

• People eating mainly untreated corn, or very poor diets low in both niacin and tryptophan
• People with chronic heavy alcohol use — a leading cause of pellagra in high-income countries today
• People with malabsorption conditions — such as Crohn’s disease or after some types of weight-loss surgery
• People with Hartnup disease — a genetic disorder that impairs tryptophan absorption, reducing the body’s ability to make niacin
• People with carcinoid syndrome — tumors that divert tryptophan into serotonin production, leaving less for niacin
• Long-term users of isoniazid (a tuberculosis drug) — which interferes with vitamin B6, needed to make niacin from tryptophan
• People with very low protein intake — and therefore little tryptophan

Pellagra — the vitamin B3 deficiency disease:

Pellagra is known for the “4 Ds”: dermatitis, diarrhea, dementia, and — if untreated — death. It was historically linked with corn-based diets in populations that didn’t use nixtamalization.

• Dermatitis: a distinctive rash on sun-exposed skin — a darkened collar around the neck (Casal’s necklace) and on the backs of the hands and forearms. The sun-exposed pattern is a key diagnostic clue.
• Diarrhea: from inflammation of the digestive tract lining
• Dementia: from effects on the nervous system — confusion, disorientation, and in advanced cases, psychosis

Pellagra was epidemic in the early 20th-century American South, particularly among poor families living largely on cornmeal, molasses, and fatback pork. In the 1910s and 1920s, Joseph Goldberger of the US Public Health Service showed that it was caused by diet, not infection — a conclusion that met years of resistance. After niacin was identified as the missing factor, enrichment of flour and bread with niacin, which began in the early 1940s, helped make pellagra rare in the US.

Earlier signs of low vitamin B3:

• Fatigue and weakness
• Loss of appetite and weight
• Skin sensitivity to sunlight
• Mouth sores and a red, inflamed tongue
• Depression, irritability, and poor concentration
• Digestive discomfort

Vitamin B3 – Excessive Doses

Upper limit (UL): in the US, 35mg a day for adults, applying to niacin from supplements and fortified foods (not niacin naturally present in food). It’s based on flushing, the first side effect to appear as doses rise. Limits are lower for children:

Source: US National Academies, via the NIH Office of Dietary Supplements. In Europe, EFSA sets separate limits for the two forms: 10mg a day for nicotinic acid and 900mg a day for nicotinamide (adults).

Niacinamide (nicotinamide) doesn’t cause flushing and is tolerated at much higher doses than nicotinic acid — 500mg twice a day has been used in skin cancer prevention trials. Very high doses, in the range of several grams a day, can cause nausea and, rarely, liver problems.

High-dose nicotinic acid (1–3g a day, used for blood lipids):

• Flushing: the most common side effect. It can be reduced by taking aspirin about 30 minutes beforehand, by using extended-release forms, and by starting at a low dose and increasing slowly. Tolerance usually develops within a few weeks.
• Liver damage: a real risk at high doses — and, paradoxically, more of a concern with over-the-counter sustained-release niacin than with immediate-release forms at the same dose. Liver function is monitored during therapeutic use.
• Higher blood sugar: nicotinic acid can raise blood glucose and worsen insulin sensitivity — important for people with diabetes or prediabetes.
• Gout: high-dose niacin can raise uric acid levels and trigger gout.
• Digestive upset: nausea, vomiting, and stomach pain, particularly with immediate-release forms taken on an empty stomach.

On vitamin B3 and cholesterol: nicotinic acid raises HDL cholesterol by about 15–35%, lowers triglycerides substantially, and lowers Lp(a) — real, meaningful changes in blood lipids. However, two large trials, AIM-HIGH and HPS2-THRIVE, found that adding niacin to statin therapy didn’t reduce heart attacks or strokes, and HPS2-THRIVE found more serious side effects, including diabetes complications, infections, and bleeding. As a result, niacin is no longer a routine part of cholesterol treatment, and some niacin-based cholesterol drugs have been withdrawn. It’s now used only in specific situations, under medical supervision.

Different Types of Vitamin B3

• Niacin (nicotinic acid): the form that causes flushing and the one studied for blood lipids. Available as immediate-release (more flushing) and extended- or sustained-release (less flushing, but more liver risk at high doses). Not the best choice for general supplementation.
• Niacinamide (nicotinamide): the amide form of vitamin B3 — no flushing and no effect on cholesterol. The best all-purpose form for meeting needs, and the form used in skin cancer prevention research. Also widely used in skincare for its barrier-supporting and anti-inflammatory effects.
• NR (nicotinamide riboside): an NAD+ precursor found naturally in small amounts in milk. Human trials show it raises NAD+ levels in the blood, but whether this translates into meaningful health benefits is still unproven.
• NMN (nicotinamide mononucleotide): one step closer to NAD+ than NR in the body’s production pathway. It’s attracting a lot of research interest, and small human trials show it raises blood NAD+ levels, but evidence of real-world health or performance benefits is still limited. Usually more expensive than NR.
• Inositol hexanicotinate (IHN): marketed as “no-flush niacin.” It releases very little free niacin in the body, so it doesn’t deliver the cholesterol effects of nicotinic acid. Not recommended for that purpose.

Which form for your goal:

Vitamin B3 – How to Take It

Niacinamide can be taken at any time of day, with or without food. Most people need no more than the amount in a multivitamin. In skin cancer prevention research, people with a history of non-melanoma skin cancer took 500mg twice a day — a dose best taken on medical advice.

Nicotinic acid (only for blood lipids, under medical supervision): doctors typically start with a low dose and increase it slowly over weeks. Taking aspirin about 30 minutes beforehand, and taking the niacin with food, reduces flushing. Over-the-counter sustained-release niacin should be avoided at high doses because of its liver risk, and liver function is monitored during treatment.

NR or NMN: typical research doses are around 250–1,000mg a day. They’re generally well tolerated in short-term studies, but long-term safety and benefits haven’t been established.

Vitamin B3 is water-soluble and stored only in small amounts, so regular intake from food matters. A few days of low intake won’t cause deficiency in a well-nourished person, but long-term low intake will.

Vitamin B3 – Interactions

Alcohol impairs vitamin B3 absorption and metabolism. Isoniazid (a tuberculosis drug) interferes with the tryptophan-to-niacin pathway by disrupting vitamin B6. High-dose nicotinic acid combined with statins may increase the risk of muscle damage (myopathy). Because high-dose nicotinic acid can raise blood sugar and uric acid, it can interfere with diabetes and gout treatment, and its blood-vessel-widening effect can add to blood pressure medications. Anyone on these medicines should only use therapeutic niacin under medical supervision.

Vitamin B3 – Synergy

• Works with vitamin B1, vitamin B2, and vitamin B5 in the shared enzyme systems of energy metabolism — all are needed for the citric acid cycle and electron transport chain to run fully.
• Depends on vitamins B2 and B6 and on iron to make niacin from tryptophan.
• Supplies the NADPH that glutathione reductase (which depends on vitamin B2) uses to recycle glutathione — working alongside selenium, which powers glutathione peroxidase.
• Works with folate and vitamin B12 — the NADPH made from niacin is needed by two key enzymes (DHFR and MTHFR) to convert folate into its active forms, which vitamin B12 then uses in the methylation cycle. Together, they support making new DNA and recycling homocysteine, while NAD+ supports DNA repair. One nuance: very high doses of nicotinamide are partly cleared from the body by methylation, which draws on the same supply of methyl groups — another reason more isn’t automatically better.
• Works with omega-3 fatty acids on blood lipids when nicotinic acid is used therapeutically — both lower triglycerides, and in a 16-week randomized trial in people with metabolic syndrome, combining prescription niacin and omega-3s improved triglycerides, HDL, and some lipoprotein particles. Early research also suggests that unsaturated fats, including omega-3s, may soften high-dose niacin’s acute effects on insulin and free fatty acids, though it isn’t yet established that they prevent niacin’s effect on blood sugar.

Vitamin B3 – Antagonistic Interactions

• Alcohol depletes NAD+ and impairs vitamin B3 metabolism.
• High-dose nicotinic acid suppresses the release of fat for fuel during exercise.
• High-dose nicotinic acid can worsen insulin sensitivity, particularly in people with diabetes or prediabetes.
• High-dose sustained-release nicotinic acid carries a risk of liver damage; liver monitoring is standard during treatment.

Food values: USDA FoodData Central — anchovies, canned in olive oil (Foundation Foods, FDC ID 2747652, niacin from SR Legacy); lamb liver, braised (SR Legacy, 172532); peanuts, raw (Foundation Foods, 2515376, niacin from SR Legacy); turkey breast, roasted (SR Legacy, 174516); venison loin, cooked (SR Legacy, 172604); light tuna, canned in water (Foundation Foods, 334194); chicken breast, braised (Foundation Foods, 331960); sunflower seeds, raw (Foundation Foods, 2515381, niacin from SR Legacy); Atlantic salmon, farmed, cooked (SR Legacy, 175168); ground beef, cooked (SR Legacy, 171797); white mushrooms, boiled (SR Legacy, 169252); whole-wheat bread (SR Legacy, 172688); brown rice, cooked (SR Legacy, 169704). RDA and upper limits from the US National Academies, via the NIH Office of Dietary Supplements. % Daily Values use the FDA’s current Daily Value of 16mg.