Niacin intake data indicate that a small percentage of the U.S. population is likely to exceed the UL. Individuals who take over-the-counter niacin to treat themselves, for example, for high blood cholesterol, might exceed the UL on a chronic basis. The UL is not meant to apply to individuals who are receiving niacin under medical supervision.

Data useful for setting the Estimated Average Requirement (EAR) for children, adolescents, pregnant women, and lactating women are scanty, but evidence suggests that niacin intake in the United States and Canada is generous relative to need. Priority should be given to studies in two areas:

• the niacin requirement to satisfy nicotinamide adenine dinucleotide (NAD) needs for increased adenosine diphosphate ribosylation resulting from oxidant-deoxyribonucleic acid damage and

• sensitive and specific blood measures of niacin status. Current assessments of niacin status and requirement are based solely on urinary metabolite measures; measurements of plasma metabolites such as the 2-pyridone derivatives may be productive. Two recent experimental studies have suggested erythrocyte NAD as a functional blood measure of niacin status (Eu et al., 1989; Ribaya-Mercado et al., 1997), but further work is needed in clinical populations.

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