PM2.5 air pollution and cause-specific cardiovascular disease mortality

Abstract

Background: Ambient air pollution is a modifiable risk factor for cardiovascular disease, yet uncertainty remains about the size of risks at lower levels of fine particulate matter (PM2.5) exposure which now occur in the USA and elsewhere.

Methods: We investigated the relationship of ambient PM2.5 exposure with cause-specific cardiovascular disease mortality in 565 477 men and women, aged 50 to 71 years, from the National Institutes of Health-AARP Diet and Health Study. During 7.5 x 106 person-years of follow up, 41 286 cardiovascular disease deaths, including 23 328 ischaemic heart disease (IHD) and 5894 stroke deaths, were ascertained using the National Death Index. PM2.5 was estimated using a hybrid land use regression (LUR) geostatistical model. Multivariate Cox regression models were used to estimate relative risks (RRs) and 95% confidence intervals (CI).

Results: Each increase of 10 μg/m3 PM2.5 (overall range, 2.9-28.0 μg/m3) was associated, in fully adjusted models, with a 16% increase in mortality from ischaemic heart disease [hazard ratio (HR) 1.16; 95% CI 1.09-1.22] and a 14% increase in mortality from stroke (HR 1.14; CI 1.02-1.27). Compared with PM2.5 exposure <8 μg/m3 (referent), risks for CVD were increased in relation to PM2.5 exposures in the range of 8-12 μg/m3 (CVD: HR 1.04; 95% CI 1.00-1.08), in the range 12-20 μg/m3 (CVD: HR 1.08; 95% CI 1.03-1.13) and in the range 20+ μg/m3 (CVD: HR 1.19; 95% CI 1.10-1.28). Results were robust to alternative approaches to PM2.5 exposure assessment and statistical analysis.

Conclusions: Long-term exposure to fine particulate air pollution is associated with ischaemic heart disease and stroke mortality, with excess risks occurring in the range of and below the present US long-term standard for ambient exposure to PM2.5 (12 µg/m3), indicating the need for continued improvements in air pollution abatement for CVD prevention.

Keywords: Air pollution; cardiovascular disease; mortality.

Figure 1.

Hazard ratios (HR), for overall and cause-specific CVD mortality, by level of fine particulate matter (PM_2.5), NIH-AARP. Hazard ratios are adjusted in Cox regression models for sex and region (six US states and two municipalities of residence, at study entry) as strata, and adjusted for age, race or ethnic group, education, marital status, body mass index (BMI), alcohol use, smoking, median income and percenage not completing high school in the census tract of residence at enrolment.

Figure 2.

Hazard ratios (HR) for major cardiovascular diseases per 10 μg/m³ level of exposure to fine particulate matter (PM_2.5), NIH-AARP. Major cardiovascular diseases (CVD) include ischaemic heart disease and stroke. Hazard ratios (HR) are adjusted in Cox regression models for sex and region (six US states and two municipalities of residence, at study entry) as strata, and adjusted for age, race or ethnic group, education, marital status, bodymass index (BMI), alcohol use, smoking, median income and percentage not completing high school in the census tract of residence at enrolment.