Background
Bisphenol A (BPA) is a well-known endocrine disrupter used in several consumer products. Restricted use of BPA has led to increased use of bisphenol F (BPF) and bisphenol S (BPS). While previous studies found no associations between prenatal BPA and BPF exposure and bone mineral density (BMD), two recent cohort studies found that prenatal BPS exposure was negatively associated with bone mineral density in the offspring.

Aim
To determine possible associations between maternal and child urinary bisphenol concentrations, BMD and bone mineral content (BMC) in 7-year-old healthy children.

Methods
Pregnant women were recruited in 2010–2012 to participate in the Odense Child Cohort (OCC), Denmark. Maternal urine samples were collected in gestational week 28 and urinary BPA concentration was measured by isotope diluted LC-MS/MS. The children delivered a urine sample at age 7 years in which BPA, BPF and BPS were measured by an extended LS-MS/MS method based on the original method. At age 7 years DXA scans were performed and BMC and Z-score for BMD calculated. Associations between osmolality adjusted urinary maternal BPA and child BPA, BPF and BPS concentrations and BMC and BMD Z-score were examined by multiple linear regression analysis adjusted for potential confounders. Additionally, a combined effect of the bisphenols were evaluated by including the sum of child urinary BPA, BPF and BPS concentrations in the statistical analyses.

Results
A total of 546 mothers and 453 children aged 7 years participated. BPA was detected in 84% and 96% of the maternal and child urine samples, respectively. We found no significant association between maternal urinary BPA concentration during pregnancy and BMC and BMD Z-score in 7-year-old children. In addition, no association between current bisphenol exposure in tertiles and bone density was found, interestingly, current BPA and summed bisphenol exposure in the highest 10% was associated with lower BMD Z-score at age 7-years, statistically significant for boys.

Conclusion
In these low exposed children we found no association between prenatal or current bisphenol exposure in tertiles and BMD in healthy children, however, the highest 10% exposed children had lower BMD, significant for boys, suggesting a negative impact with high bisphenol exposure. The short half-lives of bisphenols and the cross-sectional nature of the child exposure prompt more longitudinal studies to further clarify this topic.