ABSTRACT
Although corn consumption as a dietary staple was linked to pellagra incidence for centuries, the etiology was not clearly defined until the relationship between dietary tryptophan and its conversion to niacin was understood. Krehl et al.5 showed that tryptophan could replace nicotinic acid and prevent pellagra-like symptoms in rats. Niacin deficient rats fed corn diets were cured by feeding casein, a good tryptophan source. Later work showed that tryptophan is a precursor for the biosynthesis of nicotinic acid.6 Studies conducted from 1961 to 1980 designed to determine the contribution of dietary tryptophan to the niacin requirement led to the accepted interconversion factor of 60 to 1.7 Sixty mg of dietary tryptophan is considered equivalent to 1 mg of niacin. The concept of niacin equivalents (NEs) was introduced by Horwitt et al.8 in 1981 (1 NE equals 1 mg of niacin and 60 mg of dietary tryptophan). Dietary Reference Intakes (DRIs) are reported as mg NE to include the impact of metabolic conversion of tryptophan to the human niacin requirements.7 The historically significant role of corn diets in pellagra incidence is explained by the low levels and poor bioavailability of both tryptophan and nicotinic acid in corn.
