Bone mineral density during pregnancy in women participating in a randomized controlled trial of vitamin D supplementation

Abstract

Background: Little is known about bone mineral density (BMD) during pregnancy. Advances in technology with lower radiation emissions by dual-energy X-ray absorptiometry instruments now permit the safe measurement of BMD during pregnancy.Objective: We evaluated maternal BMD during pregnancy as a function of vitamin D status in women of diverse racial/ethnic backgrounds.Design: A total of 301 women who underwent BMD measurements at 12-20 wk of gestation and again at 0-14 wk postpartum were included in this analysis. Women were a subset of subjects who were recruited for a randomized, controlled, double-blind trial of vitamin D supplementation in pregnancy (400, 2000, or 4000 IU/d).Results: Treatment had no significant effect on changes in BMD that occurred between 12-20 wk of gestation and 0-14 wk postpartum. Similarly, changes in spine and femoral neck bone mineral contents (BMCs) were not significantly different in the treatment groups. In addition, vitamin D inadequacy (serum 25-hydroxyvitamin D concentration, averaged across pregnancy, <50 nmol/L) was not associated with changes in BMD or BMC. There were significant racial/ethnic differences in spine BMD. African Americans lost more spine BMD than did Caucasians (-0.04 ± 0.04 compared with -0.02 ± 0.04 g/cm²; P = 0.033). In addition, baseline obesity was associated with a greater loss of femoral neck BMD. The means ± SDs of femoral neck BMD loss were -0.02 ± 0.05 and 0.0 ± 0.03 g/cm² for groups with baseline body mass index (BMI; in kg/m²) ≥30 and <30, respectively.Conclusion: These findings do not support a dose effect of vitamin D supplementation on bone health and suggest that race/ethnicity and BMI play an important role in pregnancy bone health. This trial was registered at clinicaltrials.gov as NCT00292591.

Keywords: bone mineral content; bone mineral density; cholecalciferol; pregnancy; vitamin D.

FIGURE 1

Consolidated Standards of Reporting Trials diagram of pregnancy study bone mineral density subset. DXA, dual-energy X-ray absorptiometry; 25(OH)D, 25-hydroxyvitamin D.

FIGURE 2

Percentages of changes of BMD at 0–14 wk postpartum relative to BMD at 12–20 wk of gestation are shown by treatment, race, obesity status, and vitamin D status, respectively, for the cohort of 301 women. Circles represent outliers, and upper and lower bars represent ranges of data without including outliers. The upper, middle, and bottom of each box represent the 75%, 50%, and 25% quantiles of data, respectively. (A) Percentages of changes were not significantly different between treatment groups for the spine (P = 0.769) and femoral neck (P = 0.859). (B) Percentages of changes in spine BMD (P = 0.002) were significantly different in race/ethnicities, and percentages of changes in femoral neck BMD (P = 0.058) were trending. (C) Obesity tended to be associated with greater loss of spine BMD (P = 0.054) and was associated with femoral neck BMD (P < 0.001). (D) Vitamin D status was not associated with percentages of changes in spine BMD (P = 0.867) or femoral neck BMD (P = 0.104). BMI is expressed as kg/m². BMD, bone mineral density.

FIGURE 3

Changes in BMD and BMC as a function of mean 25(OH)D (n = 301). On the basis of Spearman’s rank correlation test, the mean 25(OH)D concentration during pregnancy was not associated with changes in spine BMD (r = 0.03, P = 0.591), femoral neck BMD (r = 0.07, P = 0.211), spine BMC (r = −0.05, P = 0.352), or femoral neck BMC (r = 0.07, P = 0.200), respectively. BMC, bone mineral content; BMD, bone mineral density; 25(OH)D, 25-hydroxyvitamin D.