To estimate exposure-response associations between chronic exposure to fine particulate matter (PM_2.5) and risks of the first hospital admission for major cardiovascular disease (CVD) subtypes.

Population based cohort study.

Contiguous US.

59 761 494 Medicare fee-for-service beneficiaries aged ≥65 years during 2000-16. Calibrated PM_2.5 predictions were linked to each participant’s residential zip code as proxy exposure measurements.

Risk of the first hospital admission during follow-up for ischemic heart disease, cerebrovascular disease, heart failure, cardiomyopathy, arrhythmia, valvular heart disease, thoracic and abdominal aortic aneurysms, or a composite of these CVD subtypes. A causal framework robust against confounding bias and bias arising from errors in exposure measurements was developed for exposure-response estimations.

Three year average PM_2.5 exposure was associated with increased relative risks of first hospital admissions for ischemic heart disease, cerebrovascular disease, heart failure, cardiomyopathy, arrhythmia, and thoracic and abdominal aortic aneurysms. For composite CVD, the exposure-response curve showed monotonically increased risk associated with PM_2.5: compared with exposures ≤5 µg/m³ (the World Health Organization air quality guideline), the relative risk at exposures between 9 and 10 µg/m³, which encompassed the US national average of 9.7 µg/m³ during the study period, was 1.29 (95% confidence interval 1.28 to 1.30). On an absolute scale, the risk of hospital admission for composite CVD increased from 2.59% with exposures ≤5 µg/m³ to 3.35% at exposures between 9 and 10 µg/m³. The effects persisted for at least three years after exposure to PM_2.5. Age, education, accessibility to healthcare, and neighborhood deprivation level appeared to modify susceptibility to PM_2.5.

The findings of this study suggest that no safe threshold exists for the chronic effect of PM_2.5 on overall cardiovascular health. Substantial benefits could be attained through adherence to the WHO air quality guideline.