Joint association of physical activity intensity and fine particulate matter exposure with cardiovascular disease risk in adults aged 75 years and older in South Korea

Background/Introduction Although several studies have investigated the combined effects of physical activity and fine particulate matter (PM2.5) exposure on cardiovascular disease (CVD), research focusing on older populations remains limited. Furthermore, epidemiological evidence on the protective effects of physical activity intensity against the adverse health impacts of PM2.5 exposure remains insufficient. Purpose This nationwide retrospective cohort study aimed to examine the joint association of physical activity intensity and PM2.5 exposure with CVD risk among adults aged 75 years and older in South Korea. Methods This study was based on data from the Korea National Health Insurance Service (KNHIS). Physical activity intensity was assessed in metabolic equivalents of tasks (METs)-min/week. PM2.5 levels were obtained from the National Ambient Air Monitoring System in South Korea. The joint association of METs-min/week and PM2.5 exposure for 2 years with CVD risk was evaluated using the Fine-Gray model to estimate adjusted subdistribution hazard ratios (SHRs), accounting for all-cause mortality as a competing risk. The following covariates were adjusted for in the analysis: age, sex, household income, Charlson Comorbidity Index (CCI), smoking status, alcohol consumption, body mass index, systolic blood pressure, fasting serum glucose, and total cholesterol. Participants were followed from January 1, 2017, until the onset of CVD, death, or December 31, 2021. Results The study population included 1,033,304 individuals aged 75 years and older who resided in the same location during the exposure period (2015-2016), had undergone a national health examination, and had no history of death or CVD before the index date. Among individuals exposed to low to moderate levels of PM2.5, higher METs-min/week was associated with a reduced risk of CVD (P for trend <0.001). Compared to the group with METs-min/week of 0, individuals with METs-min/week of 1000 or higher had a lower risk of CVD (adjusted SHR, 0.83; 95% CI, 0.81–0.86). Higher METs-min/week were also linked to a lower risk of CVD in individuals exposed to high levels of PM2.5 (P for trend <0.001). Individuals with METs-min/week of 1000 or more had a reduced risk of CVD compared to those with METs-min/week of 0 (adjusted SHR, 0.87; 95% CI, 0.84–0.89). There was no significant effect modification in the association between physical activity intensity and CVD risk across different PM2.5 levels (P for interaction=0.216). Conclusions This study demonstrates that, among adults aged 75 years and older, higher physical activity intensity may be associated with a reduced risk of CVD, regardless of residential PM2.5 exposure. Given the growing concerns about the health effects of environmental factors, these epidemiological findings underscore the importance of health-related interventions, such as promoting physical activity, in mitigating the risk of CVD in older adults.