ascorbate concentrations than men at a given vitamin C intake. Thus, the requirement for women is extrapolated based on body weight differences from those established for men (see Table 1-1).

EAR for Men

 

19–30 years

75 mg (426 µmol)/day of vitamin C

31–50 years

75 mg (426 µmol)/day of vitamin C

EAR for Women

 

19–30 years

60 mg (341 µmol)/day of vitamin C

31–50 years

60 mg (341 µmol)/day of vitamin C

The RDA for vitamin C is set by assuming a coefficient of variation (CV) of 10 percent (see Chapter 1) because information is not available 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). Due to the many assumptions and approximations involved, the RDA for women is rounded up to 75 mg from its calculated value of 72 mg/day.

RDA for Men

 

19–30 years

90 mg (511 µmol)/day of vitamin C

31–50 years

90 mg (511 µmol)/day of vitamin C

RDA for Women

 

19–30 years

75 mg (426 µmol)/day of vitamin C

31–50 years

75 mg (426 µmol)/day of vitamin C

Adults Ages 51 Years and Older
Evidence Considered in Estimating the Average Requirement

Some cross-sectional studies have shown that vitamin C status, as measured by plasma and leukocyte ascorbate concentrations, is lower in the elderly, especially institutionalized elderly, than in young adults (Burr et al., 1974; Cheng et al., 1985). Low blood vitamin C concentrations in institutionalized and chronically ill elderly were normalized to those of active elderly and young adults by increasing their dietary vitamin C intake, suggesting that the low levels were primarily due to poor intake (Newton et al., 1985). However, Davies et al. (1984) found that intestinal absorption of a 500-mg oral dose of ascorbic acid, as measured by urinary ascorbate excretion, was significantly less in elderly (mean age 83 years) than in younger subjects (mean age 22 years). Although this dose (500 mg/day) was about 5 times higher than the vitamin C intake of many elderly



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