able on the standard deviation of the requirement for vitamin C; the RDA is defined as equal to the EAR plus twice the CV to cover the needs of 97 to 98 percent of the individuals in the group (therefore, for vitamin C the RDA is 120 percent of the EAR).

RDA for Lactation

 

14–18 years

115 mg (653 µmol)/day of vitamin C

19–30 years

120 mg (682 µmol)/day of vitamin C

31–50 years

120 mg (682 µmol)/day of vitamin C

Special Considerations
Smokers

Evidence that smokers have lower vitamin C status than nonsmokers, even with comparable vitamin C intakes, is summarized in the preceding section “Factors Affecting the Vitamin C Requirement.” The data also show that the metabolic turnover of ascorbate in smokers is about 35 mg/day greater than in nonsmokers (Kallner et al., 1981), apparently due to increased oxidative stress and other metabolic differences. These findings indicate that smokers need additional vitamin C to provide comparable nutriture to nonsmokers.

From analysis of NHANES II data on vitamin C intakes and serum concentrations, Schectman et al. (1991) estimated that the average intake of smokers needed to be at least 200 mg/day of vitamin C in order to attain serum ascorbate concentrations equivalent to those of nonsmokers who meet the 1989 RDA of 60 mg/day (NRC, 1989). Use of population survey data to estimate an increased ascorbate requirement for smokers is questionable, because the cause and significance of the observed differences in serum ascorbate concentrations between smokers and nonsmokers are largely unknown.

From in vitro data on the loss of ascorbate in plasma exposed to cigarette smoke, it was estimated that one cigarette may consume about 0.8 mg of ascorbate, or about 32 mg/day for a two-pack-a-day smoker (Cross and Halliwell, 1993). More precise data were obtained from an experimental study of 17 apparently healthy male smokers who were administered radiolabeled tracer ascorbic acid at steady-state intakes of 30 to 180 mg/day to allow kinetic calculations of ascorbate metabolism and body pools. Results were compared with a similar protocol for nonsmokers (Kallner et al., 1979, 1981). Metabolic turnover of the vitamin was about 35 mg/day greater in smokers than in nonsmokers. Thus, to obtain a near maximal steady-state ascorbate body pool equivalent to that of nonsmok-



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