balance studies have collectively concluded that manganese balance can be achieved at around 2.1 to 2.5 mg/day (Freeland-Graves et al., 1988; Friedman et al., 1987; Hunt et al., 1998). Based on a coefficient of variation of 10 percent, balance data would yield a Recommended Dietary Allowance (RDA) of 2.5 to 3 mg/day. Based on the Total Diet Study (Appendix Table E-6), the median manganese intake for men was 2.1 to 2.3 mg/day, and the median intake for women was 1.6 to 1.8 mg/day. Because overt symptoms of a manganese deficiency are not apparent in North America, an RDA based on balance data most likely overestimates the requirement for most North American individuals. Therefore, intake data are used to set an AI for manganese. Because dietary intake assessment methods tend to underestimate the actual daily intake of foods, the highest intake value reported for the four adult age groups was used to set the AI for each gender.

There are limited data, such as fetal manganese concentration, on which to base an EAR specific to pregnancy. Casey and Robinson (1978) reported that manganese concentrations in fetal tissues ranged from 0.35 to 9.27 μg/g dry weight. In animals, manganese deficiency in utero produces ataxia and impaired otolith development, but these defects have not been reported in humans.

The additional manganese requirement during pregnancy is determined by extrapolating up from adolescent girls and adult women as described in Chapter 2. Carmichael and coworkers (1997)