Niacin is the generic name for nicotinic acid (pyridine-3-carboxylic acid), nicotinamide (niacinamide or pyridine-3-carboxamide), and related derivatives, such as nicotinamide riboside.
All tissues in the body convert absorbed niacin into its main metabolically active form, the coenzyme nicotinamide adenine dinucleotide (NAD).
More than 400 enzymes require NAD to catalyze reactions in the body, which is more than for any other vitamin-derived coenzyme. NAD is also converted into another active form, the coenzyme nicotinamide adenine dinucleotide phosphate (NADP), in all tissues except skeletal muscle.
Co-enzymes nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP), is directly or indirectly involved in many metabolic functions including the digestive system, skin, and nerves.
NAD functions as an electron carrier for intracellular respiration as well as a co-factor for enzymes involved in the oxidation (catabolism) of fats, proteins, carbohydrates and alcohol to produce energy. NAD is also required as a substrate for non-redox reactions.
These enzymes and their products seem to be involved in DNA replication, DNA repair, cell differentiation and cellular signal transduction. NADP is important for the reductive biosynthesis of fatty acids and cholesterol. Like NAD, NADP is a cofactor for enzymes, such as in the oxidation of glucose-6-phosphate to ribose-5-phosphate in the pentose phosphate pathway.
Vitamin B3 (nicotinic acid) supplements in high doses have been used successfully to lower elevated LDL (bad) cholesterol and fat (triglyceride) levels in the blood and to increase HDL (good). Vitamin B3 deficiency causes a condition called pellagra.
Niacin vitamers are found in both plant and animal foods, and due to the contribution of tryptophan, foods containing balanced protein may also contribute to high niacin equivalent.
Roles of niacin (vitamin B3) in human body
