Niacin

Niacin, also known as nicotinic acid and nicotinamide, is vitamin B3 and an essential nutrient for humans. In the body it is a precursor to the coenzymes nicotinamide adenine dinucleotide (NAD+) and nicotinamide adenine dinucleotide phosphate (NADP+), which participate in redox reactions critical to energy metabolism and biosynthetic processes.

Dietary sources include meat, fish, poultry, legumes, seeds, and fortified cereals. The body can also synthesize niacin from the amino acid tryptophan, with a conversion that requires vitamin B6, riboflavin, and iron. Niacin is absorbed mainly in the small intestine and is excreted in the urine as metabolites.

Deficiency causes pellagra, characterized by dermatitis, diarrhea, and dementia, and can be associated with conditions such as Hartnup disease or chronic alcohol use. Maize-based diets historically contributed to Pellagra in some regions unless the grain was processed (nixtamalization) to increase niacin bioavailability.

High-dose pharmacologic niacin is used to modify lipid levels, lowering triglycerides and LDL cholesterol and raising HDL cholesterol, but it can cause flushing, hepatotoxicity, hyperglycemia, and gout. For this reason, lipid-related niacin therapy is prescribed under medical supervision and is limited by adverse effects. Niacinamide (nicotinamide) is used to prevent or treat pellagra and other niacin-deficiency conditions, with less impact on lipid levels.

In addition to its nutritional role, niacin participates in multiple NAD+/NADP+-dependent enzymes involved in glycolysis, the citric acid cycle, fatty acid metabolism, and DNA repair, underscoring its broad importance in cellular energy and biosynthesis.