Interaction between long-term coarse particulate matter exposure and physical activity in relation to overall and respiratory mortality in U.S. women

BACKGROUND AND AIM: Coarse particulate matter (PM2.5-10) air pollution exposure has been linked to respiratory health and increased mortality rates, while higher physical activity has been linked to decreased mortality rates. Increased respiration during physical activity may increase PM exposure, attenuating the benefits of physical activity. We examined the interaction between long-term residential exposure to PM2.5-10 and physical activity on overall and respiratory mortality rates. METHODS: Exposure to PM2.5-10 was assigned to each residential address using a spatio-temporal model and physical activity was reported on biennial questionnaires in the Nurses’ Health Study, a U.S. nationwide prospective cohort. We determined nonaccidental death and cause of death through searching the National Death Index. We followed 106,267 women between 1988 and 2008. We used Cox proportional hazards models to assess associations with each exposure separately and jointly, adjusted for demographics, diet, and individual- and area-level socioeconomic status. RESULTS:We observed 10,928 nonaccidental deaths, of which 918 were attributed to respiratory disease. In adjusted models, 24-month average ambient PM2.5-10 exposure per 10 μg/m3 increase was associated with modest increased risk of overall mortality (HR: 1.06, 95% CI: 1.01-1.11) and respiratory mortality (HR: 1.22, 95% CI: 1.05-1.42). Increasing overall physical activity per 9 metabolic equivalent of task-hours/week increase (based on meeting weekly physical activity recommendations) was associated with decreased risk of overall mortality (HR: 0.94, 95% CI: 0.94-0.95) and decreased risk of respiratory mortality (HR: 0.90, 95% CI: 0.88-0.91). We observed no interactions between PM2.5-10 exposure and physical activity. CONCLUSIONS:Exposure to PM2.5-10 was associated with increased risk of overall and respiratory mortality. Higher physical activity was associated with decreased overall and respiratory mortality; this association remained at all levels of PM2.5-10 experienced in this study, suggesting that the benefits of physical activity outweigh the negative impacts of air pollution exposures. KEYWORDS: air pollution, particulate matter, long-term exposure, respiratory outcomes, mortality