A LONGITUDINAL-STUDY OF URINARY CALCIUM, MAGNESIUM, AND ZINC EXCRETION IN LACTATING AND NONLACTATING POSTPARTUM WOMEN

Postpartum lactating (n = 12) and nonlactating (n = 11) women and neve r pregnant women (n = 14) collected urine samples and diet records 2 d each month for 6 mo to determine whether postpartum women conserved u rinary calcium, magnesium, or zinc. Mean daily excretions were analyze d by repeated-measures analysis of variance and covariance to assess g roup and time effects. Lactating women excreted less urinary calcium ( 1-6 mo) than never pregnant (n = 8) and nonlactating (n = 4) women who did not use oral contraceptives (P < 0.01); however, excretion rose ( P < 0.05) by 3 mo postpartum. In the nonlactating and never pregnant g roups, women using oral contraceptives excreted less urinary calcium t han the other women (P < 0.01). Lactating women excreted less urinary zinc (1-6 mo) than did control and nonlactating women (P < 0.01). Mech anisms may possibly be operating during lactation that depress urinary calcium for greater than or equal to 2 mo and urinary zinc less than or equal to 6 mo postpartum.