Nicotinic acid, also known as niacin or vitamin B3, is a water-soluble vitamin whose derivatives such as NADH, NAD, NAD+, and NADP play essential roles in energy metabolism in the living cell and DNA repair. The designation vitamin B3 also includes the amide form, nicotinamide or niacinamide. Severe lack of niacin causes the deficiency disease pellagra, whereas a mild deficiency slows down the metabolism decreasing cold tolerance. The recommended daily allowance of niacin is 2-12 mg a day for children, 14 mg a day for women, 16 mg a day for men, and 18 mg a day for pregnant or breast-feeding women. It is found in various animal and plant tissues and has pellagra-curative, vasodilating, and antilipemic properties. The liver can synthesize niacin from the essential amino acid tryptophan (see below), but the synthesis is extremely slow and requires vitamin B6; 60 mg of tryptophan are required to make one milligram of niacin. Bacteria in the gut may also perform the conversion but are inef

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