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Pregnancy

Evidence Considered in Estimating the Average Requirement

Direct studies of the requirement for vitamin A during pregnancy are lacking. The model used to establish the EAR is based on the accumulation of vitamin A in the liver of the fetus during gestation and an assumption that liver contains approximately half of the body’s vitamin A when liver stores are low, as in the case of newborns. Liver vitamin A concentrations for full-term stillborn infants (Dorea et al., 1984; Hoppner et al., 1968; Montreewasuwat and Olson, 1979; Olson, 1979) have ranged from less than 10 to greater than 100 μg/g liver, with values tending to be skewed towards the lower range (Olson, 1979). A vitamin A concentration of 1,800 μg per liver for 37 to 40 week gestation age (Montreewasuwat and Olson, 1979) was used to calculate a concentration of 3,600 μg per fetus. Assuming the efficiency of maternal vitamin A absorption to average 70 percent and vitamin A to be accumulated mostly in the last 90 days of pregnancy, the mother’s requirement would be increased by approximately 50 μg/day during the last trimester. Because vitamin A in the mother’s diet may be stored and mobilized later as needed and some vitamin A may be retained in the placenta, the EAR is estimated to be ~50 μg/day in addition to the EAR for nonpregnant adolescent girls and women for the entire pregnancy period.

Vitamin A EAR and RDA Summary, Pregnancy

EAR for Pregnancy

 

14–18 years

530 μg RAE/day of vitamin A

19–30 years

550 μg RAE/day of vitamin A

31–50 years

550 μg RAE/day of vitamin A

The RDA for vitamin A is set by using a CV of 20 percent based on the calculated half-life values for liver vitamin A (see “Adults Ages 19 Years and Older”). The RDA is defined as equal to the EAR plus twice the CV to cover the needs of 97 to 98 percent of individuals in the group (therefore, for vitamin A the RDA is 140 percent of the EAR). The calculated values for the RDAs have been rounded up to the nearest 10 μg.



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