Chapter 13 – Niacin

Niacin is required for the biosynthesis of the pyridine nucleotides NAD(H) and NADP(H), through which it has key roles in metabolism. Niacin is the generic descriptor for pyridine 3-carboxylic acid and derivatives exhibiting the biological activity of nicotinamide. Sources of dietary niacin include yeasts and meats, although it is also found in vegetables. Humans and other animals can also synthesize NAD(H) and NADP(H) from tryptophan. Niacin is water soluble. Prior to absorption, NAD(H) and NADP(H), the forms found in most animal-derived foods, are digested to release NAm, which is absorbed through carrier-mediated, facilitated diffusion. As the essential component of NAD(H) and NADP(H), which function as intermediates in most of the hydrogen transfers in metabolism, niacin contributes to over 500 reactions in the metabolism of carbohydrates, fatty acids, and amino acids. As niacin can be synthesized from tryptophan, dietary deficiency is uncommon. Deficiency results in pellagra, which affects the skin, gastrointestinal tract, and nervous system.