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Background:

Increased respiration during physical activity may increase air pollution dose, which may attenuate the benefits of physical activity on cardiovascular disease (CVD) risk and overall mortality.

Objectives:

We aimed to examine the multiplicative interaction between long-term ambient residential exposure to fine particulate matter $<2.5\text{\hspace{0.17em}microns}$ (${\mathrm{PM}}_{2.5}$) and physical activity in the association with CVD risk and overall mortality.

Methods:

We followed 104,990 female participants of the U.S.-based prospective Nurses’ Health Study from 1988 to 2008. We used Cox proportional hazards models to assess the independent associations of 24-months moving average residential ${\mathrm{PM}}_{2.5}$ exposure and physical activity updated every 4 y and the multiplicative interaction of the two on CVD (myocardial infarction and stroke) risk and overall mortality, after adjusting for demographics and CVD risk factors.

Results:

During 20 years of follow-up, we documented 6,074 incident CVD cases and 9,827 deaths. In fully adjusted models, ${\mathrm{PM}}_{2.5}$ exposure was associated with modest increased risks of CVD [hazard ratio (HR) for fifth quintile $\ge 16.5{\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$ compared to first quintile $<10.7{\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$: 1.09, 95% confidence interval (CI): 0.99, 1.20; $p_{\text{trend}}=0.05$] and overall mortality (HR fifth compared to first quintile: 1.10, 95% CI: 1.02, 1.19; $p_{\text{trend}}=0.07$). Higher overall physical activity was associated with substantially lower risk of CVD [HR fourth quartile, which was $\ge 24.4\text{\hspace{0.17em}metabolic}$ equivalent of task (MET)-h/wk, compared to first quartile ($<3.7\text{MET-h}/\mathrm{wk}$): 0.61, 95% CI: 0.57, 0.66; $p_{trend}<0.0001$] and overall mortality (HR fourth compared to first quartile: 0.40, 95% CI: 0.37, 0.42; $p_{trend}<0.0001$). We observed no statistically significant interactions between ${\mathrm{PM}}_{2.5}$ exposure and physical activity (overall, walking, vigorous activity) in association with CVD risk and overall mortality.

Discussion:

In this study of U.S. women, we observed no multiplicative interaction between long-term ${\mathrm{PM}}_{2.5}$ exposure and physical activity; higher physical activity was strongly associated with lower CVD risk and overall mortality at all levels of ${\mathrm{PM}}_{2.5}$ exposure. https://doi.org/10.1289/EHP7402