Long-term particulate matter exposure and bone mineral density in the Women’s Health Initiative

Abstract

BACKGROUND AND AIM: Ambient particulate matter air pollution 10 μm (PM10) concentrations have been associated with several outcomes, but few studies have examined their association with bone mineral density (BMD). Previous studies have suggested an effect of air pollution on bone health, but none has evaluated its impact in postmenopausal women. METHODS: We studied the longitudinal PM10-BMD association among 5,080 postmenopausal women in the Women’s Health Initiative Clinical Trials (WHI-CT). We used log-normal, ordinary kriging to estimate daily mean PM10 concentrations (μg/m3) at geocoded participant addresses. We averaged the means over 1-, 3-, and 5-year periods before triennial, dual energy X-ray absorptiometry (DXA) exams. We estimated total hip, lumbar spine, and total body BMD (in g/cm2) and their corresponding T-scores. We estimated the association of PM10 with BMD and T-scores using multivariable linear mixed models while controlling for correlation of repeated measures among participants and adjusting for age at DXA, race/ethnicity, income, body mass index (kg/m2), smoking status, coffee consumption, physical activity, CT randomization arm, US region of residence, and DXA equipment serial number. Multiple imputation was done for missing data. RESULTS:At baseline, women were aged 50-79 years, 78% were White, 40% were college graduates, and 71% earned $40,000/year. PM10 concentrations at baseline were cross-sectionally associated with both hip, lumbar spine, and whole-body BMD and T-scores (p 0.05). Longitudinally, lumbar spine BMD decreased 0.052 (95% confidence interval [95%CI]: 0.067, 0.037) g/cm2/year per 10% (2.21 ug/m3) increase in 5-year mean PM10 concentration. Lumbar spine T-scores also decreased with increasing duration of the 3- and 5-year mean PM10 concentrations: -0.362 Standard Deviations (SD) (-0.490, -0.235) and -0.512 SD (-0.649, -0.375), respectively. No association was seen with changes in hip or total body BMD. CONCLUSIONS:This is the first study suggesting an inverse association of ambient PM10 with BMD among postmenopausal women. KEYWORDS: Air pollution, long-term, PM10, bone mineral density, t-score, osteoporosis.