AUTHOR Dr. Carlos Orozco (BSc, MSc, ND, MD, PhD, FPAMS).
Niacin (nicotinic acid and nicotinamide) is also known as vitamin B3. Both nicotinic acid and nicotinamide can serve as the dietary source of vitamin B3.
Niacin is required for the synthesis of the active forms of vitamin B3, nicotinamide adenine dinucleotide (NAD+) and nicotinamide adenine dinucleotide phosphate (NADP+). Both NAD+ and NADP+ function as cofactors for numerous dehydrogenase reactions e.g., lactate and malate dehydrogenases.
Niacin is not a true vitamin in the strictest definition since it can be derived from the amino acid L-tryptophan, but this conversion is inefficient and requires the presence of thiamine, pyridoxine, and riboflavin.
Biological Function of Vitamin B3
Niacin functions in the release of energy from carbohydrates, fats, and proteins. Niacin is also involved in the synthesis of protein, fat, and pentoses needed for nucleic acid formation.
Niacin is a major constituent of the coenzyme nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP). These compounds function to remove hydrogen atoms during biological reactions. Niacin functions as a component of the coenzymes nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP). These enzymes are involved in respiration where they act as hydrogen acceptors. They are essential in the reactions involved in the release of energy from carbohydrates, fats, and proteins.
Oxidation-reduction (redox) reactions
Living organisms derive most of their energy from oxidation-reduction (redox) reactions, which are processes involving the transfer of electrons. As many as 200 enzymes require the niacin coenzymes, NAD and NADP, mainly to accept or donate electrons for redox reactions. NAD functions most often in reactions involving the degradation (catabolism) of carbohydrates, fats, proteins, and alcohol to produce energy. NADP functions more often in biosynthetic (anabolic) reactions, such as in the synthesis of fatty acids and cholesterol.
Signs and Symptoms of Deficiency
Pellagra, dermatitis, muscular weakness, general fatigue, anorexia, indigestion, insomnia, irritability, stress, depression, excessive blood cholesterol, autoimmune diseases, gastrointestinal upsets, inflammation of the mouth and digestive track. Memory loss, glossitis, confusion, hyper pigmentation, malignant carcinoid tumor, stomatitis, nausea and vomiting.
- Food and Nutrition Board, Institute of Medicine. Riboflavin. Dietary Reference Intakes: Thiamin, Riboflavin, Niacin, Vitamin B-6, Vitamin B-12, Pantothenic Acid, Biotin, and Choline.
- WashingtonD.C.: NationalAcademy Press; 1998:87-122. (National Academy Press).
- Brody T. Nutritional Biochemistry. 2nd ed. San Diego: Academic Press; 1999