Modifying role of physical activity in associations between air pollutants and blood pressure among cancer survivors.

High blood pressure (BP) has been linked to ambient air pollution, and cancer survivors may be particularly vulnerable due to an immune imbalance. We investigated the association between air pollution mixtures and BP among cancer survivors, and evaluated effect modification by physical activity (PA). We included 2,487 cancer survivors in the Korea National Health and Nutrition Examination Survey (2007–2021). The individual and joint associations of three-year average exposures to PM2.5, PM10, CO, NO2, and SO2 with BP were assessed using linear regression models and quantile-based g-computation (QGC), stratified by PA levels. The associations of PM and CO with higher diastolic blood pressure (DBP) were observed in the low PA group (β = 0.60, 95% CI = 0.21, 0.99, P-interaction = 0.018 for PM2.5; β = 1.24, 95% CI = 0.64, 1.83, P-interaction = 0.020 for PM10; β = 1.20, 95% CI = 0.41, 2.00 for CO). Similarly, the associations of air pollution mixtures with DBP were observed only in the low PA level (Ψ = 0.95, 95% CI = 0.30, 1.61 for PM2.5-based mixture; Ψ = 0.71, 95% CI = 0.10, 1.31 for PM10-based mixture), with PM contributing most (70–96%). Our findings suggest that PM and CO are associated with higher DBP among cancer survivors, with PM having the greatest contribution. PA may attenuate the hypertensive effects of air pollution.