Impact of long-term temporal trends in fine particulate matter (PM2.5) on associations of annual PM2.5 exposure and mortality: An analysis of over 20 million Medicare beneficiaries

Sex-difference in air pollution-related acute circulatory and respiratory mortality and hospitalization

BACKGROUND

Numerous studies have estimated adverse effects of short-term exposure to ambient air pollution on public health. Few have focused on sex-differences, and results have been inconsistent. The purpose of this study was three-fold: to identify sex-differences in air pollution-related health outcomes; to examine sex-differences by cause and season; and to examine time trends in sex-differences.

METHODS

Daily data were collected on circulatory- and respiratory-related mortality (for 29 years) and cause-specific hospitalization (for 17 years) with hourly concentrations of ozone (O3), nitrogen dioxide (NO2), and fine particulate matter (PM2.5). For hospitalization, more specific causes were examined: ischemic heart disease (IHD), other heart disease (OHD), cerebrovascular disease (CEV), chronic lower respiratory diseases (CLRD), and Influenza/Pneumonia (InfPn). Generalized Poisson models were applied to 24 Canadian cities, and the city-specific estimates were combined for nationwide estimates for each sex using Bayesian hierarchical models. Finally, sex-differences were tested statistically based on their interval estimates, considering the correlation between sex-specific national estimates.

RESULTS

Sex-differences were more frequently observed for hospitalization than mortality, respiratory than circulatory health outcomes, and warm than cold season. For hospitalization, males were at higher risk (M > F) for warm season (OHD and InfPn from O3; IHD from NO2; and InfPn from PM2.5), but F > M for cold season (CEV from O3 and OHD from NO2). For mortality, we found F > M only for circulatory diseases from ozone during the warm season. Among the above-mentioned sex-differences, three cases showed consistent time trends over the years: while M > F for OHD from O3 and IHD from NO2, F > M for OHD from NO2.

CONCLUSIONS

We found that sex-differences in effect of ambient air pollution varied over health outcome, cause, season and time. In particular, the consistent trends (either F > M or M > F) across 17 years provide stronger evidence of sex-differences in hospitalizations, and warrant investigation in other populations.

The impact of Long-Term PM2.5 constituents and their sources on specific causes of death in a US Medicare cohort

BACKGROUND

Our understanding of the impact of long-term exposures to PM_2.5 constituents and sources on mortality is limited.

OBJECTIVES

To examine associations between long-term exposures to PM_2.5 constituents and sources and cause-specific mortality in US older adults.

METHODS

We obtained demographic and mortality data for 15.4 million Medicare beneficiaries living within the conterminous United States (US) between 2000 and 2008. We assessed PM_2.5 constituents exposures for each beneficiary and used factor analysis and residual-based methods to characterize PM_2.5 sources and mixtures, respectively. In age-, sex-, race- and site- stratified Cox proportional hazard models adjusted for neighborhood socio-economic status (SES), we assessed associations of individual PM_2.5 constituents, sources, and mixtures and cause-specific mortality and examined modification of these associations by participant demographics and location of residence. We assessed the robustness of our findings to additional adjustment for behavioral risk factors and to alternate exposure definitions and exposure windows.

RESULTS

Hazard ratios (HR) were highest for all causes of death, except COPD, for PM_2.5 constituents and the coal combustion-related PM_2.5 components, with no evidence of confounding by behavioral covariates. We further found Pb and metal-related PM_2.5 components to be significantly associated with increased HR of all causes of death, except COPD and lung cancer mortality, and nitrate (NO₃^-) and silicon (Si) and associated source-related PM_2.5 components (traffic and soil, respectively) to be significantly associated with increased all-cause, CVD, respiratory and all cancer-related mortality HR. Associations for other examined constituents and mortality were inconsistent or largely null. Our analyses of mixtures were generally consistent with these findings. Mortality HRs were greatest for minority, especially Black, low-income urban, younger, and male beneficiaries.

DISCUSSION

PM_2.5 components related to coal combustion, traffic, and to a lesser extent, soil were strongly associated with mortality from CVD, respiratory disease, and cancer.

Fine particulate air pollution and human mortality: 25+ years of cohort studies

Much of the key epidemiological evidence that long-term exposure to fine particulate matter air pollution (PM_2.5) contributes to increased risk of mortality comes from survival studies of cohorts of individuals. Although the first two of these studies, published in the mid-1990s, were highly controversial, much has changed in the last 25 + years. The objectives of this paper are to succinctly compile and summarize the findings of these cohort studies using meta-analytic tools and to address several of the key controversies. Independent reanalysis and substantial extended analysis of the original cohort studies have been conducted and many additional studies using a wide variety of cohorts, including cohorts constructed from public data and leveraging natural experiments have been published. Meta-analytic estimates of the mean of the distribution of effects from cohort studies that are currently available, provide substantial evidence of adverse air pollution associations with all-cause, cardiopulmonary, and lung cancer mortality.