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. 2015;126:20–45.

Fig. 1.

Fig. 1

The principal forms of niacin are nicotinic acid and nicotinamide. Both are usually derived from food, but the body can synthesize nicotinamide from tryptophan. Niacin is a component of (among other things) the coenzymes NAD+ and NADH, the numerous functions of which—including the synthesis of ATP, explain the protean manifestations of pellagra.