B3

B3, also known as niacin, is a water-soluble vitamin in the B-complex family. In humans it exists in two principal coenzyme forms, nicotinamide adenine dinucleotide (NAD) and NAD phosphate (NADP), which are essential for oxidoreductase reactions in cellular metabolism. Niacin can be ingested as nicotinic acid or nicotinamide, and the body can also synthesize small amounts from the essential amino acid tryptophan, with about 60 mg of dietary tryptophan yielding 1 mg of niacin equivalents (NE).

Dietary sources include meat, fish, poultry, fortified cereals, legumes, and seeds. The body’s use of niacin is commonly expressed as NE to reflect tryptophan conversion; foods vary in their NE content.

B3 plays a central role in energy production and metabolism, supporting reactions that generate ATP from carbohydrates, fats, and proteins. It is also involved in DNA repair and cell signaling through NAD- and NADP-dependent enzymes, making it important for multiple physiological processes.

Deficiency causes pellagra, historically linked to corn-based diets or conditions that limit intake or absorption. Pellagra is characterized by dermatitis, diarrhea, and dementia, and can be fatal if untreated. At-risk groups include individuals with chronic alcohol use, malabsorption disorders, or severe malnutrition.

Recommended intakes for adults are generally in the mid-teens of niacin equivalents per day (about 14–16 mg NE, depending on sex and guidelines). The tolerable upper intake level for supplemental niacin is commonly set around 35 mg NE per day to reduce the risk of adverse effects, such as flushing and potential liver toxicity from high-dose nicotinic acid. Niacin is also prescribed at high doses under medical supervision to treat dyslipidemia.