hibited an indirect correlation with the breath content of ethane, a volatile marker of lipid peroxidation, even though the pregnant women were receiving supplements with 320 mg/day of vitamin C (Schwarz et al., 1995). Thus, pregnant women in these special sub-populations should consume additional vitamin C.

Lactation
Evidence Considered in Estimating the Average Requirement

As indicated earlier, infants fed human milk are estimated to consume on average 40 mg/day vitamin C during the first 6 months of life. Salmenpera (1984) reported that the vitamin C intake of 47 mothers during prolonged lactation ranged from 48 to 277 mg/day, mean 138 mg/day. Three mothers in this study who consumed less than 100 mg/day of vitamin C demonstrated plasma ascorbate values below the lower limit of normal [less than 10 µmol/L (0.2 mg/dL)]. Women who consumed 100 to 199 mg/day of vitamin C produced milk with 100 mg/L of vitamin C (Byerley and Kirksey, 1985). Maternal vitamin C intake in excess of 200 mg/day resulted in increased urinary excretion of vitamin C but did not increase the content of the vitamin in human milk (Byerley and Kirksey, 1985). It is thought that a regulatory mechanism in the mammary gland prevents the elevation of milk vitamin C concentrations beyond that level seen when urinary execretion increases representing blood saturation (Byerley and Kirksey, 1985).

Vitamin C EAR and RDA Summary, Lactation

To estimate the EAR for lactation, the average vitamin C produced in milk, 40 mg/day during the first 6 months of lactation, is added to the EAR for the nonlactating women. Although the vitamin C content of human milk declines with length of lactation and milk volume declines with the addition of solid foods, the EAR is not decreased for longer periods of lactation.

EAR for Lactation

 

14–18 years

96 mg (545 µmol)/day of vitamin C

19–30 years

100 mg (568 µmol)/day of vitamin C

31–50 years

100 mg (568 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 avail-



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