gestational diabetes (Bardicef et al., 1995). It is not known whether this is a sequellae of the condition or a factor in its causation.

Pregnant Adolescents, Multiparous Births. A prospective study of 53 nulliparous teenagers found no difference in serum or erythrocyte magnesium concentrations between those pregnant adolescents who developed pregnancy-induced hypertension and those who had normal term deliveries, with both groups having decreasing concentrations of magnesium over gestation (Boston et al., 1989). However, Caddell and coworkers (1975) found a greater renal retention of a parenteral load of magnesium in pregnant adolescents and women with twin pregnancies, suggesting that magnesium requirements during these periods may be increased.

Lactation
Indicators Used to Set the EAR

Human Milk Content. The concentration of magnesium in human milk averages between 25 to 35 mg (1.0 to 1.5 mmol)/liter and is not influenced by the mother 's magnesium intake (Moser et al., 1983, 1988). Assuming a milk production of 780 ml/day, a lactating woman may secrete from 9 to 26 mg (0.4 to 1.1 mmol)/day of magnesium in her milk (Allen et al., 1991).

Despite the secretion of magnesium in milk during lactation, plasma and erthyrocyte magnesium concentrations do not differ between lactating and nonlactating women at daily magnesium intakes of approximately 250 mg (10.4 mmol) (Moser et al., 1983), and milk concentrations do not change throughout lactation (Dewey et al., 1984; Moser et al., 1983; Rajalakshmi and Srikantia, 1980).

Balance Studies. A magnesium balance study in six lactating women, six nonlactating postpartum women, and seven women who were never pregnant found lower urinary magnesium concentrations in lactating women compared with women who were never pregnant (Dengel et al., 1994). A positive magnesium balance of 20 mg (0.84 mmol)/day was reported in lactating women consuming a daily magnesium intake of 217 mg (9 mmol). However, there was only a 5-day adaptation period, and although the women appeared to conserve magnesium, the small number of subjects may have lead to an insufficient ability to detect a difference. Whether the increased bone resorption that occurs during lactation contributes to the mag-



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement