Sex-specific associations between ambient air pollution exposure thresholds and lung function in middle-aged and...

Ambient air pollution is associated with reduced lung function, but whether sex modifies the association with threshold-based exposures remains unclear. This cross-sectional study examined sex-specific associations between threshold-based exposures to fine particulate matter (PM_2.5), nitrogen dioxide (NO₂), ozone (O₃), and lung function.

Data from 21,339 adults aged 45-85 years in the Canadian Longitudinal Study on Aging were analyzed. Annual average air pollutant concentrations representing multi-year exposure estimates (2012-2015) were assigned to participants based on their residential postal codes. Decision tree regression was used to derive exposure cut points and classify participants into low, intermediate, and high exposure thresholds for each pollutant with respect to lung function (FEV₁, FVC, and FEV₁/FVC ratio). Survey-weighted multivariable linear regression models were used to estimate sex-specific associations with percent-predicted lung function, including interaction terms between sex and exposure thresholds.

Significant sex interactions were observed for PM_2.5 and NO₂ with percent-predicted FEV₁ and FVC, and for O₃ with percent-predicted FVC and the FEV₁/FVC ratio. Among males, high vs. low PM_2.5 exposure was associated with lower FEV₁ (-3.11%; 95% CI: -4.47, -1.74) and FVC (-2.72%; 95% CI: -3.76, -1.69). Among females, a significant but smaller FVC reduction was observed (-1.53%; 95% CI: -2.59, -0.47) but not for FEV₁. High vs. low NO₂ exposure was associated with greater reductions in FEV₁ among males (-5.00%; 95% CI: -7.16, -2.84) than among females (-1.99%; 95% CI: -2.79, -1.19), and significantly reduced FVC among males(-3.58%; 95% CI: -5.15, -2.00) but not among females (-1.64%; 95% CI: -3.39, 0.11). High vs. low O₃ exposure was associated with reduced FVC in both sexes, with a stronger association among males (-3.34%; 95% CI: -4.37, -2.31) than among females (-2.60%; 95% CI: -3.56, -1.65).

Sex significantly modified the inverse associations between ambient air pollution exposure thresholds and lung function, with greater reductions observed in males. These associations occurred at exposure thresholds at or below current regulatory standards, underscoring the need for continuous reassessment of air quality guidelines to better protect respiratory health.