Niacin

Niacin, or vitamin B3, is a water-soluble vitamin the body needs to convert food into usable energy and to support over 400 enzymatic reactions, including DNA repair and antioxidant activity. The body can also make a small amount from the amino acid tryptophan. Meat, poultry, fish, fortified grains, and legumes are the main dietary sources.

What is niacin

Niacin functions as a building block for two coenzymes — NAD and NADP — that participate in energy metabolism throughout the body; Harvard T.H. Chan School of Public Health, The Nutrition Source notes these coenzymes support more than 400 enzymes involved in converting nutrients into energy, synthesizing cholesterol and fats, repairing DNA, and acting as antioxidants. Dietary intake is measured in "niacin equivalents" because the body can convert the amino acid tryptophan into niacin. Harvard's Nutrition Source lists red meat, poultry, fish, brown rice, fortified cereals, nuts, seeds, legumes, and bananas as natural sources, and notes that outright deficiency is uncommon in industrialized countries because of grain fortification. In this project's data, concentrated non-fortified sources by measured amount include baker's yeast, canned anchovies in oil, and raw yellowfin tuna, alongside everyday staples like brown rice and peanuts.

Health benefits of niacin

• Energy metabolism and cellular repair. Niacin's core, well-established role is as a precursor to coenzymes used across hundreds of metabolic and DNA-repair reactions, per Harvard's Nutrition Source.
• Cholesterol management — evidence has moved against routine use. At pharmacological doses (1,000–2,000 mg/day, far above the RDA), nicotinic acid supplements can raise HDL cholesterol and lower LDL cholesterol. However, Harvard's Nutrition Source reports that more recent randomized trials have been disappointing: niacin supplementation, including when added to statin therapy, did not reduce heart attacks, strokes, or cardiovascular deaths in these trials, and a Cochrane review found no reduction in overall or cardiovascular deaths. The U.S. FDA subsequently concluded that niacin's benefit no longer outweighs its risk when combined with statins. This is a case where the evidence base does not support the once-common use of high-dose niacin for heart disease prevention.

How much you need

The NIH Office of Dietary Supplements RDA for niacin, corroborated via WebSearch and independently confirmed by Harvard's directly-fetched page, is 16 mg niacin equivalents (NE)/day for adult men and 14 mg NE/day for adult women, rising to 18 mg NE/day during pregnancy and 17 mg NE/day during lactation. The Tolerable Upper Intake Level (UL) is 35 mg/day for adults, a limit set specifically to avoid the skin flushing that nicotinic acid supplements can cause at doses above typical dietary intake — a different and much lower threshold than the multi-gram doses used medically for cholesterol management. These figures are not yet populated in this project's nutrient_rda table.

Signs of deficiency and excess

Severe, prolonged niacin deficiency causes pellagra, which MedlinePlus describes as digestive problems, inflamed skin, and impaired mental function; Harvard's Nutrition Source adds that the characteristic pellagra rash is dark and scaly on sun-exposed skin, often accompanied by a red, swollen tongue. Harvard notes risk is concentrated in people with very limited diets, chronic alcohol use, or carcinoid syndrome (a tumor that diverts tryptophan away from niacin production), rather than the general population. At the other end, excess niacin — almost always from supplements rather than food — is best known for causing skin flushing (warmth, redness, itching, or tingling of the face, neck, arms, or chest) from nicotinic acid specifically; MedlinePlus also lists elevated blood glucose, peptic ulcers, and skin rashes among documented effects of excess intake, and Harvard's Nutrition Source notes that very high doses (3,000–9,000 mg/day sustained over months to years) have been associated with liver inflammation in severe cases.

Warnings & interactions

Flushing from nicotinic acid supplements can be reduced by using extended- or sustained-release formulations, and by avoiding hot beverages and alcohol around the time of dosing, per MedlinePlus; nicotinamide (a different form of vitamin B3) does not cause flushing due to its distinct chemical structure. High-dose niacin therapy, historically prescribed alongside statins for cholesterol management, is now understood — per Harvard's Nutrition Source, citing the FDA's own conclusion — to carry risk that isn't offset by cardiovascular benefit when combined with statins, which is why this combination has fallen out of favor. Very high sustained doses (in the thousands of milligrams per day) carry a documented risk of liver inflammation. None of these concerns apply to niacin obtained from food; they are specific to high-dose supplemental or prescription use, which should be medically supervised rather than self-directed.

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