Background: Ambient air pollution exposures have been frequently linked to cardiovascular disease (CVD) morbidity and mortality. However, less is known about the populations most susceptible to these adverse effects. Methods and Results: We assessed the associations of long‐term particulate matter (PM) exposures with incident CVD in a nationwide cohort of 114 537 women in the Nurses’ Health Study, and performed analyses to identify subpopulations at the greatest risk. Residential address level time‐varying monthly exposures to PM 2.5, PM 10, and PM 2.5 to 10 microns in diameter were estimated from spatio‐temporal prediction models. In multivariable models, increases in all size fractions of PM were associated with small, but not statistically significant, increased risks of total CVD, coronary heart disease, and stroke. PM‐associated CVD risks were statistically significantly higher among women with diabetes as compared to those without (P‐for‐interaction <0.0001 for PM 10 and PM 2.5 and 0.007 for PM 2.5 to 10). For each 10 μg/m3 increase in 12‐month average PM 2.5, PM 2.5 to 10, and PM 10, the multivariable adjusted hazard ratios were 1.44 (95% CI: 1.23 to 1.68), 1.17 (95% CI: 1.05 to 1.30), and 1.19 (95% CI: 1.10 to 1.28) among women with diabetes. There were also suggestions of higher risks among older (≥70 years) women, the obese, and those living in the Northeast and South. Smoking status and family history did not consistently modify the association between PM and CVD, and risks were most elevated with exposures in the previous 12 months. Conclusions: In this nationwide cohort, women with diabetes were identified as the subpopulation most sensitive to the adverse cardiovascular health effects of PM
