Air pollution and bone mineral density among Women’s Health Initiative participants: A mixture analysis

BACKGROUND AND AIM: Ambient air pollution has been associated with bone damage, but no studies have examined the role of mixtures (i.e., biological effective components) on bone mineral density (BMD) in postmenopausal women. METHODS: We conducted a prospective study using data from the Women’s Health Initiative (WHI, N=9,041 at baseline, postmenopausal women aged 50 to 79 years from 1993 to 1998). We included participants in both the Clinical Trials (CT) and Observational Study (OS), but only those with BMD and air pollution data were included. We used log-normal, ordinary kriging to estimate daily mean PM10 concentrations, NOx, NO2, and SO2 at geocoded participant addresses. We averaged the mean concentrations over 1-, 3-, and 5-year periods before BMD assessments (and T-scores) at the whole-body, total hip, femoral neck, and spine using dual-energy X-ray absorptiometry. After multiple imputation of missing covariates data, we estimated air pollutant-BMD associations in multivariable linear and linear mixed-effects models controlling for correlation of repeated measures and adjusting for several covariates. We also estimated air pollutant mixture-BMD associations using Bayesian kernel machine regression (BKMR). RESULTS: At baseline, women were on average 63.29 years old (SD: 7.39 years). In cross-sectional analyses, 1-, 3-, and 5-year mean PM10, NOx, NO2, and SO2 were inversely associated with all BMD sites as well as T-scores. In longitudinal analyses, 1- and 5-year mean PM10, NOx, NO2, and SO2 were associated with whole-body BMD. These results suggest that, for example, lumbar spine BMD decreased 0.023 (95%CI: 0.017, 0.028) g/cm2/year per 10% increase in 5-year mean NO2 concentration. Similar associations were observed at other BMD sites. BKMR suggested that only NO2 was inversely associated with BMD at all sites. CONCLUSIONS: Our findings suggest air pollution, particularly NO2, has clinically relevant effects on BMD and potentially fracture risk in postmenopausal women. KEYWORDS: Air pollution, bone, osteoporosis.