Long-term exposure to fine particulate matter modifies the association between physical activity and the risk of...

The trade-off between the potentially detrimental effects of fine particulate matter (PM_2.5) and the benefits of physical activity (PA) is unclear. We aimed to explore the independent and interaction effects between long-term PM_2.5 exposure and PA on blood pressure (BP) and hypertension. A total of 8704 adults (≥45 years) without hypertension at baseline in a nationwide cohort of the China Health and Retirement Longitudinal Study (CHARLS) were followed from 2011 to 2015. The participants were selected using a four-stage, stratified, and cluster sampling procedure. The annual PM_2.5 concentrations at the residential address were estimated from a two-stage machine learning model with a 10 km × 10 km resolution. A standard questionnaire collected information on PA and potential confounders, and metabolic equivalents (MET·h/wk), which combined frequency, intensity, and duration information, were used to assess PA levels. We adopted mixed-effects regression models to explore the independent and interaction effects between long-term PM_2.5 exposure and PA on BP and risk of hypertension. Systolic blood pressure (SBP) decreased by -0.84 mmHg (95% CI: -1.34, -0.34) per an IQR (interquartile range, 175.5 MET·h/wk) increase in PA, and diastolic blood pressure (DBP) decreased by -0.42 mmHg (95% CI: -0.76, -0.07). Each IQR (36.1 μg/m³) increment in PM_2.5 was associated with 0.48 mmHg (95% CI: -0.24, 1.20) in SBP and -0.02 mmHg (95% CI: -0.44, 0.39) in DBP. PM_2.5 showed an elevated effect with risks of hypertension (odds ratio, OR = 1.01; 95% CI: 1.00, 1.03), while PA showed the inverse result (OR = 0.98; 95% CI: 0.97, 0.99). Interaction analyses indicated PA maintained the beneficial effects on BP, but the negative association was attenuated, accompanied by the increase of PM_2.5. PA decreased the BP and hypertension risks, while PM_2.5 showed the opposite results. PM_2.5 attenuated the beneficial effects of PA on BP and modified the association between PA and the risk of hypertension.