Calcium homeostasis and bone metabolism during pregnancy, lactation, and postweaning: a longitudinal study

Abstract

Ten women were followed serially to determine the effect of stages of reproduction on calcium and bone metabolism. The study periods were nonpregnant nonlactating, the end of each trimester of gestation, 3 mo lactation, and postweaning. Comparisons were with nonpregnant nonlactating status for each individual. Fractional calcium absorption (P < 0.0001) and concentrations of 1,25-dihydroxyvitamin D (P < 0.01) were higher in the second and third trimesters. Total urinary calcium was higher during pregnancy and lower postweaning. Parathyroid hormone (PTH) concentrations were higher only postweaning (P < 0.01). Markers of bone turnover increased at the third trimester and during lactation: serum tartrate resistant acid phosphatase and bone specific alkaline phosphatase, and urinary deoxypyridinoline (P < 0.01). Serum procollagen I carboxypeptides increased only in the third trimester (P < 0.01). Bone mineral density by single-photon absorptiometry did not differ by period. We conclude that absorption and urinary excretion of calcium increase during pregnancy whereas bone turnover increases during late pregnancy and lactation; only renal changes consistent with an increase in PTH were seen postweaning.

Bone mineral density and calcium metabolism of Hong Kong Chinese postpartum women—a 1-y longitudinal study

“…However, due to the low rate of exclusive breastfeeding rate in Hong Kong (Chan et al, 2000b) and the long-term follow-up, the present study was limited by small sample size. Other similar studies have also been limited by small sample sizes, with number of lactating subjects ranging from 9 to 26 (Hayslip et al, 1989;Cross et al, 1995;Krebs et al, 1997;Ritchie et al, 1998). This study confirmed previous studies that lactation is associated with a decrease in BMD and this effect is particularly pronounced at the lumbar spine and femoral neck (Kolthoff et al, 1998).…”

“…Cross et al (1995) found elevated iPTH but not 1,25(OH) 2 D postweaning compared with lactation whereas Kalkwarf et al (1996) found elevated 1,25(OH) 2 D but not iPTH postweaning compared with postpartum in nonlactating control subjects. Recent findings also suggest that BMD change during lactation is not associated with iPTH, 1,25(OH) 2 D and 25(OH)D. In contrast, prolactin, estradiol and parathyroid hormone related-peptide may be alternative mechanisms associated with bone loss and recovery during and subsequent to lactation (Sowers et al, 1996(Sowers et al, , 1998.…”

Calcium economy in human pregnancy and lactation

“…Ca absorption efficiency increases approximately 2-fold during pregnancy in association with increased expression of enterocytic Ca-binding protein (3,67,144) . As with bone resorption, this increase occurs before the third trimester, ahead of peak fetal bone accretion, and is, therefore, likely to be in anticipation of, rather than being driven by, the increased requirement for Ca (145) .…”

“…As with bone resorption, this increase occurs before the third trimester, ahead of peak fetal bone accretion, and is, therefore, likely to be in anticipation of, rather than being driven by, the increased requirement for Ca (145) . The increase in 24 h urinary Ca excretion during pregnancy (3,13,67,144) is considered to be due to the combined effects of the increase in intestinal Ca absorption and the higher glomerular filtration rate associated with pregnancy and not to a change in fractional renal Ca reabsorption (3,146,147) . Fasting Ca excretion, corrected for creatinine clearance, is normal or decreased (3,103) .…”

“…Post-lactation has been associated with decreases in urinary Ca excretion (115,144) or no difference (95) and with increases in intestinal Ca absorption efficiency (148) . Differences in the timing of the return of menses may complicate these findings (3) ; these effects are not apparent several months after breast-feeding has ceased (154) .…”