Negative balance of calcium during lactation in marginally nourished women

Abstract

Thirty-three rural Mexican women (age, 18-36y; weight, 50.3 ± 3kg; height, 148.3 ± 2cm) were studied under metabolic balance conditions. The objectives were to study the metabolic balances of calcium and phosphorus at the 1st, 3rd, and 6th months of lactation and postweaning and to determine the incorporation of calcium and phosphorus in milk. Subjects were divided into 5 groups of 5 to 10 each, representing: the 1st, 3rd, and 6th month of lactation, postweaning, and a control group of nonpregnant, nonlactating women. Metabolic balance was determined using identical diets and analysis of 24-hour urine (3 d), 72-hour feces, and 24-hour milk samples. Calcium content was determined by atomic absorption spectrophotometry and phosphorus by a colorimetric method. Calcium content in milk was similar at the 1st, 3rd, and 6th months. Positive calcium balances were observed in the control group, while balances were very negative in all lactation groups (-721.6 ± 248mg/d). Calcium urinary excretion was higher in the control and postweaning groups (P < 0.05), suggesting a regulatory mechanism to conserve calcium during lactation. No differences were observed in phosphorus content in milk at the 1st, 3rd, and 6thmonths. Positive balances were observed in the control and postweaning groups (331 ± 139 and 87.1 ± 130mg/d, respectively, mean ± SD), while the lactation groups presented more subjects (∼75%) in negative balance (mean ± SD of -180.6 ± 392 to -439 ± 146mg/d). High fecal calcium and phosphorus excretion (-1, 500mg/d) likely contributed to the negative balance during lactation.