Niacine

Niacine, also known as niacin or nicotinic acid, is a water-soluble B vitamin (vitamin B3). It occurs in two main forms: nicotinic acid and nicotinamide (niacinamide). In the body, niacin is converted into the coenzymes nicotinamide adenine dinucleotide (NAD) and NAD phosphate (NADP), which are essential for many oxidation–reduction reactions in energy metabolism, as well as for DNA repair and cell signaling.

Dietary sources include meat, fish, poultry, enriched cereals, legumes, nuts, and mushrooms. Niacin can also be synthesized from the essential amino acid tryptophan, but this requires adequate protein intake and energy.

Recommended intake varies by age and sex. For adults, typical guidelines express requirements as niacin equivalents (NE); around 14–16 NE per day are suggested for most adults, with higher needs for some groups. A tolerable upper intake level (UL) of about 35 mg/day from supplements and fortified foods is commonly cited to minimize adverse effects.

Deficiency causes pellagra, characterized by the three Ds: dermatitis (often in sun-exposed areas), diarrhea, and dementia; untreated cases can be fatal. Pellagra is rare in countries with diverse diets and fortified foods but can occur with malnutrition, alcoholism, or disorders that impair absorption or metabolism of niacin.

Pharmacologically, high-dose niacin can lower triglycerides and raise HDL cholesterol, but such use is limited by side effects, including facial flushing (often prostaglandin-mediated), itching, hepatotoxicity, and potential hyperuricemia. For this reason, niacin therapy is typically monitored by healthcare providers and is not used as a routine lipid-lowering agent in all patients.

Safety and interactions depend on dose and formulation; dietary amounts are generally safe, while higher doses require medical supervision.