Effect of calcium supplementation in pregnancy on maternal bone outcomes in women with a low calcium intake

Abstract

Background: Mobilization of maternal bone mineral partly supplies calcium for fetal and neonatal bone growth and development.

Objective: We investigated whether pregnant women with low calcium intakes may have a more extensive skeletal response postpartum that may compromise their short- or long-term bone health.

Design: In a subset of participants (n = 125) in a double-blind, randomized, placebo-controlled trial (International Trial Registry: ISRCTN96502494) in pregnant women in The Gambia, West Africa, with low calcium intakes (approximately 350 mg Ca/d), we measured bone mineral status of the whole body, lumbar spine, and hip by using dual-energy X-ray absorptiometry and measured bone mineral status of the forearm by using single-photon absorptiometry at 2, 13, and 52 wk lactation. We collected blood and urine from the subjects at 20 wk gestation and at 13 wk postpartum. Participants received calcium carbonate (1500 mg Ca/d) or a matching placebo from 20 wk gestation to parturition; participants did not consume supplements during lactation.

Results: Women who received the calcium supplement in pregnancy had significantly lower bone mineral content (BMC), bone area (BA), and bone mineral density (BMD) at the hip throughout 12 mo lactation (mean +/- SE difference: BMC = -10.7 +/- 3.7%, P = 0.005; BA = -3.8 +/- 1.9%, P = 0.05; BMD = -6.9 +/- 2.6%, P = 0.01). The women also experienced greater decreases in bone mineral during lactation at the lumbar spine and distal radius and had biochemical changes consistent with greater bone mineral mobilization.

Conclusions: Calcium supplementation in pregnant women with low calcium intakes may disrupt metabolic adaptation and may not benefit maternal bone health. Further study is required to determine if such effects persist long term or elicit compensatory changes in bone structure.

FIGURE 1

Effect of the calcium supplement in pregnancy on size-adjusted bone mineral content (SA-BMC) of the lumbar spine, distal radius, and total hip at 2, 13, and 52 wk postpartum. SA-BMC = bone mineral content adjusted for bone area (or bone width), weight, and height. Bars and error bars represent the mean ± SE percentage differences in SA-BMC relative to the placebo group at 2 wk postpartum in the calcium group (solid bars) and placebo group (open bars). Dotted lines represent the apparent time trend within each group. An “x” on the x axes denotes placebo value at 2 wk postpartum and is used as the reference and set at zero. Results were obtained from Scheffé post hoc tests for time × group interaction terms in hierarchical repeated-measures ANOVA models that included subject (nested by group), time, group, and time × group interaction. The P values depicted are for the comparison of calcium and placebo groups at each time point. The numbers of subjects at 2, 13, and 52 wk, respectively, were as follows—for the lumbar spine: 23, 29, and 40 in the calcium group and 27, 29, and 39 in the placebo group; for the distal radius: 53, 53, and 48 in the calcium group and 60, 54, and 45 in the placebo group; and for the total hip: 20, 25, and 39 in the calcium group and 23, 27, and 37 in the placebo group.