The variance in requirements cannot be determined from the available data for either men or women. Thus, a CV of 10 percent is assumed for both cases. This results in an RDA for men ages 31 through 50 years for magnesium of 420 mg (17.5 mmol) and for women, 320 mg (13.3 mmol)/day.

Balance Studies. The results of five balance studies for men aged 51 through 70 years are shown in Table 6-4. Balance studies cited in Table 6-3 (aged 31 through 50 years) by Kelsay et al. (1979), Kelsay and Prather (1983), Mahalko et al. (1983), and Spencer et al. (1994) included some male subjects in this age range, so these data are also included in this age group. Schwartz et al. (1984) assessed magnesium balance in eight males, mean age 53 ± 5 years and mean weight 67 ± 14 kg (148 ± 31 lb). A positive magnesium balance was found in the men who consumed an average intake of 381 mg (15.9 mmol)/day of magnesium (5.9 mg or 0.25 mmol/kg/day on the average).

No studies have been reported for women in this age group.

A mean daily magnesium intake of 381 mg (15.9 mmol) maintained balance in all eight subjects in the Schwartz et al. (1984) study, following a 30-day adaptation period. This would indicate that, in the absence of other studies that might demonstrate different results, the EAR should be less than 380 mg (15.8 mmol) in order to prevent magnesium loss. This study, along with those discussed above in the other adult age groups, indicates that the EAR can be expected to be somewhere between 330 and 380 mg (13.8 and 15.8 mmol)/day. Given the lower body weights in the Schwartz et al. (1984) study compared with those in the younger age groups, the magnesium intakes per kg body weight are greater (approxi-