Exposure-response associations between chronic exposure to fine particulate matter and risks of hospital admission for major cardiovascular diseases: population based cohort study.

Objective: 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.
Design: Population based cohort study.
Setting: Contiguous US.
Participants: 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.
Main Outcome Measures: 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.
Results: 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/m ³ (the World Health Organization air quality guideline), the relative risk at exposures between 9 and 10 µg/m ³ , which encompassed the US national average of 9.7 µg/m ³ 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/m ³ to 3.35% at exposures between 9 and 10 µg/m ³ . 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 .
Conclusions: 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.
Competing Interests: Competing interests: All authors have completed the ICMJE uniform disclosure form at www.icmje.org/disclosure-of-interest/ and declare: support from the National Institutes of Health (NIH) and Alfred P Sloan Foundation for the submitted work. FD reports funding from NIH and Alfred P Sloan Foundation; JDS reports funding from NIH. All other authors declare no support from any organization for the submitted work; no financial relationships with any organizations that might have an interest in the submitted work in the previous three years, no other relationships or activities that could appear to have influenced the submitted work.
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