METABOLIC BALANCE OF CALCIUM AND PHOSPHORUS DURING LACTATION IN MEXICAN RURAL WOMEN

Objective. To compare the balance of calcium (Ca) and phosphorus (P) b etween lactation and weaning, and to determine the Ca and P milk produ ction in Mexican rural lactating women. Methods. Thirty-six women aged 18-36 y, weight 49 +/- 3 kg and height 148 +/- 2 cm, were divided in six groups: four groups of lactation (1(st), 3(rd), 6(th) and 12(th) m onth) one post-weaning group and one of non pregnant non lactating wom en. The balance studies were performed collecting duplicate diets, 24h urine for 3 days, 72h feces and 24h milk samples for 2 days. The Ca c ontent was determined by atomic absorption spectrophotometry and P by the molybdate method. Results and conclusions. Ca content in milk was higher in the 3(rd) month of lactation. The Ca balances were negative in all lactation groups (789 +/- 165 mg/d). Ca urinary excretion was l ower in the lactating group (p<0.05) suggesting a regulatory mechanism to conserve Ca during lactation. No differences were observed in the P content in milk and positive balances of P were observed in the non lactating and the post-weaning groups, whereas they were negative in t he lactation groups (115 to 475 mg/d). High fecal Ca and P excretion ( similar to 1300 mg/d) was observed, which contributed to the negative condition of the balance during lactation. The production of Ca and P in the milk of these rural women was similar to the one seen in rural and urban groups in Africa, Asia, Europe and the U.S.