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

The trade-off between the potentially detrimental effects of fine particulate matter (PM2.5) and the benefits of physical activity (PA) is unclear. We aimed to explore the independent and interaction effects between long-term PM2.5 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 PM2.5 concentrations at the residential address were estimated from a two-stage machine learning model with a 10 km x 10 km resolution. A standard questionnaire collected information on PA and potential confounders, and metabolic equivalents (MET center dot 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 PM2.5 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 center dot 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 mu g/m(3)) increment in PM2.5 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. PM2.5 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 PM2.5. PA decreased the BP and hypertension risks, while PM2.5 showed the opposite results. PM2.5 attenuated the beneficial effects of PA on BP and modified the association between PA and the risk of hypertension.