[Interrelations of the calcium concentration in breast milk with maternal intake of cow's milk and milk products, bone resorption and bone mineral density during lactation].

The interrelations of the calcium (Ca) concentration in breast milk with maternal intake of cow's milk and milk products, 24-hour urinary hydroxyproline and Ca concentrations adjusted by creatinine (H.P/Cre, Ca/Cre) and bone mineral density measured by ultrasonic bone densitometry were examined to study the mechanism regulating the calcium concentration in breast milk. Subjects were 105 lactating women, aged 21 to 42 years, at 21.590 days postpartum. 1) The geometric means (logarithmically transformed calculated M +/- SD) of H.P/Cre were 40.7 (31-61) and 36.3 (28-47) mg/g in women lactating less than 150 days and 150 days or more, respectively. These values indicated increased bone resorption. 2) Intake of cow's milk and milk products significantly negatively correlated with urinary H.P/Cre. For women consuming less than 100ml per day of cow's milk, a significant positive correlation was found between the urinary H.P/Cre and Ca concentration in breast milk. These results suggest that the extent of bone resorption depends on maternal Ca intake and the Ca transfer from maternal bone to breast milk in women with a low Ca intake. 3) For women with a cow's milk intake of less than 100ml per day, a significant positive correlation was found between the Ca concentration in breast milk and bone mineral density, indicating that women with bone mineral loss are not able to compensate for the low Ca level in breast milk. 4) Urinary Ca/Cre significantly negatively affected the Ca concentration in breast milk. This result indicates that some amount of Ca in breast milk is due to renal conservation.