Niacin, also known as nicotinic acid or vitamin B3, is a vitamin whose derivatives NAD, NADH, NAD+, and NADP play essential roles in energy metabolism in the living cell and DNA repair. The designation vitamin B3, whose chemical formula is C5H4NCOOH (or alternatively, C6H6NO2), also includes the corresponding amide nicotinamide, or niacinamide, whose chemical formula is C6H6N2O. Niacin is one of the B vitamins (vitamin B complex), a group of chemically distinct, water-soluble vitamins that also includes thiamine, riboflavin, pantothenic acid, biotin, pyridoxine, folic acid, and others. Once considered to be a single vitamin, vitamin B is now seen as a complex of different vitamins that generally are found in the same foods. Vitamins are organic (carbon-containing) nutrients obtained through the diet and essential in small amounts for normal metabolic reactions. The conversion of niacin to NAD and NADP, and the use of these coenzymes in intricate biological processes like the citric acid cycle, reveals the complex coordination in living organisms.
