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ORIGINAL RESEARCH COMMUNICATION |
1 From the Facultad de Ciencias Basicas, Universidad del Atlantico, Barranquilla, Colombia (CLVZ); Instituto de Química, Universidade Federal do Rio de Janeiro (CMD); the US Department of Agriculture/Agricultural Research Service, Western Human Nutrition Research Center, Davis, CA (LRW); the US Department of Agriculture/Agricultural Research Service, Children’s Nutrition Research Center, Baylor College of Medicine, Houston (SAA); the Laboratory of Growth and Development, California Pacific Medical Center, San Francisco (EMS); and the Children’s Hospital Oakland Research Institute, Oakland, CA (JCK)
Background: Physiologic adjustments in calcium homeostasis during pregnancy and lactation in women with marginal calcium intakes have not been described.
Objective: The objective was to examine longitudinal changes in various aspects of calcium homeostasis during pregnancy and lactation in 9 healthy Brazilian women who habitually consumed 
500 mg Ca/d.
Design: Calcium homeostasis was assessed at 3 time points: 10–12 (early pregnancy, EP) and 34–36 (late pregnancy, LP) wk of pregnancy and 7–8 wk postpartum (early lactation, EL). At each time point, the following variables were measured: dietary calcium intake with a 3-d weighed food record, 24-h urinary calcium excretion (UCa), intestinal calcium absorption (%CaAbs) via administration of stable calcium isotopes with a breakfast meal, serum 1,25-dihydroxyvitamin D, parathyroid hormone (PTH), insulin-like growth factor I (IGF-I), and biochemical markers of bone turnover.
Results: Dietary calcium did not change during the study. %CaAbs increased from 69.7 ± 5.4% (
± SEM) during EP to 87.6 ± 4.5% during LP (P < 0.05) and returned to 65.1 ± 6.2% during EL. Compared with EP, UCa decreased 22% during LP and 68% during EL (P < 0.05). The net mean change in calcium retention was 212 mg/d during LP and 182 mg/d during EL. Several significant associations were found between the main outcome variables (%CaAbs, UCa, and markers of bone turnover) and serum hormones, especially IGF-I and PTH.
Conclusions: Calcium homeostasis appears to be attained by a more efficient intestinal calcium absorption during pregnancy and by renal calcium conservation during both pregnancy and lactation. IGF-I and PTH seem to play major roles in the adjustment of calcium metabolism during pregnancy and lactation.
Key Words: Pregnancy • lactation • calcium intake • calcium absorption • urinary calcium • calciotropic hormones • insulin-like growth factor I • Brazilian women
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