Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline

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DRI Dietary Reference Intakes: For Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline

and cystic maculopathy. However, there are very few cases in the literature (Fraunfelder et al., 1995). Doses of 1.5 to 5 g/day of niacin have been associated with ocular effects (Fraunfelder et al., 1995; Gass, 1973; Millay et al., 1988). Niacin-induced ocular effects appear to be reversible and dose dependent.

Summary

Flushing is the adverse effect first observed after excess niacin intake and is generally observed at lower doses than are other effects. Flushing that results in patients deciding to change the pattern of niacin intake (i.e., reduce the amount taken at a time or withdraw from treatment) was selected as the most appropriate endpoint on which to base a UL. Although nicotinamide appears not to be associated with flushing effects, a UL for nicotinic acid that is based on flushing is considered protective against potential adverse effects of nicotinamide. The data on hepatotoxicity are considered less relevant to the general population because they involve large doses taken for long periods of time for the treatment of a medical condition.

Dose-Response Assessment

Adults

Data Selection. The data sets used to identify the lowest-observed-adverse-effect level (LOAEL) for niacin included anecdotal reports and clinical trials involving oral intake of niacin by healthy individuals. Studies involving parenteral administration were not considered in the dose-response assessment. Studies involving immediate-release forms of niacin were considered more relevant to niacin intake by the general population than were studies involving sustained-release forms.

Identification of a LOAEL. The data are not adequate to identify a no-observed-adverse-effect level (NOAEL) for flushing. To identify a LOAEL, flushing reactions were considered if they resulted in a patient either changing the form or amount of niacin used or with-drawing from treatment. A LOAEL of 50 mg/day was identified based on a study by Sebrell and Butler (1938) in which four (66 percent) of six persons experienced a flushing sensation after oral intake of 50 mg/day of nicotinic acid given with meals for 92 days. In one of the four subjects who experienced flushing effects, the

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