Niacin is a general name for nicotinic acid (pyridine-3-carboxylic acid) and nicotinamide (niacinamide or pyridine-3-carboxamide) and niacin is considered an essential vitamin that is grouped with the B vitamins. Niacin is considered a vitamin because its absence can result in the deficiency disease pellagra, and this can be reversed through addition of niacin to the diet. However, whilst niacin (as a group) is considered a vitamin, nicotinamide can be synthesised in the liver from tryptophan, and then the resulting nicotinamide is distributed to other tissues around the body to perform its metabolic role in energy production. The synthesis of nicotinamide can be affected by a number of factors including disease, other nutrients, toxins and chemicals. Roughly 67 mg of tryptophan is needed to produce around 1 mg of nicotinamide in the liver, a ratio that is increased during late pregnancy when there may be an increased requirement for the vitamin. Therefore whilst niacin is considered a vitamin, a dietary intake of adequate tryptophan, in the absence of factors that increase requirement, can allow for enough niacin to cover the metabolic requirement of the vitamin.
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