Women's bone health trajectories from pregnancy to postpartum: Associations with bone-seeking metal exposure mixtures during pregnancy

Exposure to metals can impact bone health in women during sensitive periods. However, the longitudinal effect of exposure to a metal mixture on bone strength trajectories during peri-pregnancy is unknown. Our study included pregnant women from the PROGRESS cohort with metal exposures and bone strength z-scores of the radius (n = 329) and proximal phalanx (n = 270). Bone strength z-scores were assessed using quantitative ultrasound during the 3rd trimester, and 1 and 6 months postpartum. We then averaged levels of bone-seeking metals in blood (Pb, Mn) and urine (Cd, Ba, Al) assessed during pregnancy. Metals were jointly linked as a single exposure mixture with prospective bone strength z-scores using Bayesian Varying Coefficient Kernel Machine Regression. We observed that a quartile increase in Al levels was positively associated with radius z-scores at 3rd trimester of pregnancy [β = 0.10 (95 % CI: 0.02, 0.18)], while a quartile increase in Cd levels was negatively associated with radius z-score trajectories from the 3rd trimester across postpartum [β = -0.30 (95 % CI: −0.49, −0.11)]. We also observed several negative associations between Mn [β = -0.10 (95 % CI: −0.18, −0.03)], Pb [β = -0.09 (95 % CI: −0.16, −0.02)], or Al [β = -0.12 (95 % CI: −0.21, −0.03)] with phalanx z-score levels at pregnancy, but that did not persist throughout the postpartum trajectory. Stratified models indicated potential differential effects in mothers carrying a male fetus compared to mothers carrying a female fetus. Our study findings indicate overall deleterious effects from metals on bone strength in pregnancy and at postpartum.