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in areas exposed to sunlight; changes in the digestive tract that are associated with vomiting, constipation or diarrhea, and a bright red tongue; and neurological symptoms including depression, apathy, headache, fatigue, and loss of memory. Pellagra was common in the United States and parts of Europe in the early twentieth century in areas in which corn or maize (which is low in both niacin and the amino acid tryptophan) was the dietary staple. Although a worldwide problem, pellagra has virtually disappeared from industrialized countries except for its occurrence in chronic alcoholism and in individuals with conditions that disrupt tryptophan pathways. It still appears in India and parts of China and Africa. For example, pellagra was reported in Mozambican refugees in Malawi (Malfait et al., 1993).

SELECTION OF INDICATORS FOR ESTIMATING THE REQUIREMENT FOR NIACIN

Niacin status and dietary requirement can be estimated by using biochemical or clinical endpoints of niacin deficiency. Biochemical changes occur well before the appearance of overt signs of deficiency. Biochemical markers include daily urinary excretion of methylated metabolites, the ratio of 2-pyridone to N1-methyl-nicotinamide in urine, erythrocyte pyridine nucleotides, oral dose uptake tests, erythrocyte nicotinamide adenine dinucleotide (NAD), and plasma 2-pyridone derivative.

Urinary Excretion

The most reliable and sensitive measures of niacin status are urinary excretion of the two major methylated metabolites, N1-methyl-nicotinamide and its 2-pyridone derivative (N1-methyl-2-pyridone-5-carboxamide). Criteria for interpreting urinary N1-methyl-nicotinamide excretion amounts in adults and pregnant women indicate that for adults, 24-hour excretion rates of less than 5.8 µmol/day represent deficient niacin status and 5.8 to 17.5 µmol/day represents low status (Sauberlich et al., 1974). The ratio of the 2-pyridone to N1-methyl-nicotinamide, although independent of age and creatinine excretion, is a measure of protein adequacy rather than niacin status (Shibata and Matsuo, 1989). It is relatively insensitive to a marginal niacin intake of 10 mg/day of niacin equivalents (NEs) and has been shown to be not totally reliable for evaluating an intake of 6 mg/day of NEs (Jacob et al., 1989). The ratio of the 6-pyridone (N1-methyl-nicotinamide-3-carboxamide) to N1-methyl-



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