take on 15 apparently healthy volunteers. Subjects ingested 1, 5, and 10 g/day supplemental ascorbate at mealtime for 5 days, separated by 5 days of no supplementation. This study reported diarrhea in 2 of the 15 subjects taking 10 g/day. These subjects were unable to continue at this dose

The above human data suggest that an intake of vitamin C greater than 3 g/day is likely to cause osmotic diarrhea in many individuals, although some reports involving a few individuals suggest this may occur at 3 g/day. Thus, the 3-g/day intake is considered a LOAEL.

Uncertainty Assessment. There is little uncertainty regarding the range of vitamin C intakes that are likely to induce osmotic diarrhea. An uncertainty factor (UF) of 1.5 was selected to extrapolate the LOAEL to a NOAEL. Thus, the 3 g/day intake is considered a LOAEL, and a NOAEL of 2 g/day is estimated for adult humans. Because the database has no other significant sources of uncertainty and because of the mild, reversible nature of osmotic diarrhea caused by high vitamin C intakes, no further uncertainty factors are necessary.

Derivation of a UL. The LOAEL of 3 g/day was divided by the UF of 1.5 to obtain a NOAEL and UL value of 2 g/day.

Vitamin C UL Summary, Ages 19 Years and Older

UL for Adults

 

19 years and older

2,000 mg (11,360 µmol)/day of vitamin C

Other Life Stage Groups

Infants. For infants, the UL was judged not determinable because of insufficient data on adverse effects in this age group and concern about the infant 's ability to handle excess amounts. Potential concerns for high vitamin C concentrations in infants stem from isolated reports of anecdotal rebound scurvy, oxidative damage, and hemolysis (Ballin et al., 1988; Cochrane, 1965; Powers et al., 1995). To prevent high levels of intake, the only source of intake for infants should be that available from food and formula.

Children and Adolescents. Limited data exist on vitamin C toxicity in toddlers, children, and adolescents. Ludvigsson et al. (1977) con-



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