Body stores Both acid and amide forms of the vitamin are readily absorbed from the small intestine. These coenzymes are formed in the blood, kidney, brain and liver. The main storage organ, the liver, may contain a significant fraction of the bioavailable vitamin, but there is little storage of niacin as such. Excretion is through urinary metabolites, the most common of which is N 1 -methylnicotinamide. Both nicotinamide and nicotinic acid are stable when exposed to heat, light, air and alkali.
Little loss occurs in the cooking and storage of foods.
Principal function Niacin is involved in reactions that generate energy in tissues by the biochemical conversion of carbohydrates, fats and proteins. The two coenzymes, NAD and NADP, are essential for utilizing the metabolic energy of foods. Niacin is essential for growth and is involved in the synthesis of hormones. Principal antagonists Copper deficiency can inhibit the conversion of tryptophan to niacin. The pathway from tryptophan to niacin is sensitive to a variety of nutritional alterations.