Social determinants of vulnerability to nitrogen oxide- and sulfur dioxide-related bone damage among postmenopausal women in the United States

Abstract

Background: Studying social determinants of health (SDOH) in air pollutant-related bone loss among aging women may help identify bone health disparities, design preventive strategies, and inform policy. Prolonged exposure to air pollution is associated with decreased bone mineral density (BMD) and increased fracture risk in later life. However, the extent to which socioeconomic status (SES) contributes to pollution-related bone damage remains unclear.

Methods: We estimated the extent to which social determinants of health (SDOH) modify the associations of nitrogen oxides (NOx) and sulfur dioxide (SO₂)-induced bone damage. We analyzed the Women's Health Initiative (WHI) data from the randomized clinical trial (RCT) (n = 4,202) and the observational study (OS) (n = 4,839), totaling 9,041 women. Ambient concentrations of nitrogen dioxide (NO₂), nitrogen oxide (NO), and SO₂, averaged over 1-, 3-, and 5-year periods preceding bone mineral density (BMD) assessment, were the exposures. Individual- and neighborhood-level SDOH (self-reported educational attainment, annual family income, and neighborhood-level socioeconomic status (nSES) were evaluated as potential effect modifiers. BMD at the lumbar spine, total hip, and whole body were modeled as outcomes using linear mixed models.

Results: A 10% increase in NO₂ was suggestively associated with 1.4-3.8 times greater BMD loss in low vs. high nSES participants across all sites. For example, 1-year lumbar spine BMD loss per 10% NO₂ increase was β = -0.047 (95% CI, -0.066 to -0.027) in the low nSES compared with β = -0.013 (95% CI, -0.023 to -0.001) in the high nSES group (p-interaction = 0.001). Similarly, suggestive associations were also observed for NO. nSES interactions were null for SO₂. For income, NO was suggestively associated with lumbar spine bone loss across all exposure periods, whereas only the 3-year average NO₂ exposure was suggestively associated with whole-body BMD (p = 0.048). Again, no interaction was observed for SO₂. Participants with lower education showed greater NO-related lumbar spine bone. SO₂ showed the opposite pattern at multiple sites, while NO₂ showed no associations.

Conclusion: Neighborhood-level analyses revealed suggestive associations between bone mineral loss and a broader range of air pollutants. Reducing social inequities may improve the bone health of older women living in areas with high air pollution. Additional studies are needed to generalize the findings to younger women and men, as only older women were analyzed.

Keywords: bone mineraI density; nitrogen oxide (NO) x; postmenopausal women; social determinants of health; sulfur dioxide.