Calcium homeostasis during pregnancy and lactation in Brazilian women with low calcium intakes: a longitudinal study.
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 approximately 500 mg Ca/d.


METHODS
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.
Facultad de Ciencias Basicas, Universidad del Atlantico, Barranquilla, Colombia.
Carmiña L
CL
Vargas Zapata
Carmen M
CM
Donangelo
Leslie R
LR
Woodhouse
Steven A
SA
Abrams
E Martin
EM
Spencer
Janet C
JC
King
D000328:Adult; D001938:Brazil; D002136:Calcium, Dietary / Q000008:administration & dosage / Q000378:metabolism* / Q000493:pharmacokinetics; D005260:Female; D006706:Homeostasis / Q000502:physiology*; D006801:Humans; D007408:Intestinal Absorption; D007774:Lactation / Q000378:metabolism*; D008137:Longitudinal Studies; D011247:Pregnancy
D002136:Calcium, Dietary