Air Pollutant Exposure Linked to Global Cardiovascular, Respiratory Mortality

Short-term exposure to particulate matter (PM) is independently associated with daily all-cause, cardiovascular, and respiratory mortality in persons across 600-plus cities in the world, according to a new study.

The assessment of daily air pollution exposure data from 652 cities in 24 countries or regions by a team of international investigators delivered a comprehensive understanding of how inhaled PM₁₀ and fine PM_2.5 exposure affects persons globally.

Led by Cong Liuc, MS, Renjie Chen, PhD, Antonio Gasparrini, PhD, and Haidong Kan, PhD, investigators conducted the systemic evaluation using health and environmental data from the Multi-City Multi-Country (MCC) Collaborative Research Network, which provided the regions with available air pollution data running from 1986-2015.

They classified observed causes of death based on ICD-9 and -10 codes for cardiovascular and respiratory disease. Daily PM₁₀ data was obtained in 598 cities, and PM_2.5 in 499 cities. The two-stage, multicity time-series analysis included the following steps:

• An estimation of cityspecific PM concentration associations with mortality using generalized additive models
• A comparison of lag day varieties to determine appropriate lag time for PM and temperature, using generalized crossvalidation scores
• A pooled estimate of cityspecific associations of PM concentrations with mortality, conducted with random-effects models
• A report of the pooled estimate, along with related 95% confidence intervals (CI) as the percentage change in daily mortality per 10 mcg per cubicmeter increase in PM concentrations

Their final analysis included 20.1 million deaths from cardiovascular diseases, and 5.6 million from respiratory disease. The average annual mean PM₁₀ concentration in 598 cities was 56.0 mcg per cubic meter. For PM_2.5, the mean concentration in 499 cities was 35.6 mcg per cubic meter.

Investigators observed a strong correlation between the 2 measures of PM, with a mean Pearson correlation coefficient of 0.78.

An average increase of 10 mcg per cubic meter in the two-day moving average of PM₁₀ concentration—the representative average over the current and previous day—was associated with increases of 0.44% (95% CI, 0.39 — 0.50) in daily all-cause mortality; 0.36% (95% CI, 0.30 – 0.43) in daily cardiovascular mortality; and 0.47% (95% CI, 0.35 – 0.58) in daily respiratory mortality.

For daily mortality increases with same-change PM_2.5 concentration, investigators reported all-cause increase of 0.68% (95% CI, 0.59 — 0.77); cardiovascular increase of 0.55% (95% CI, 0.45 – 0.66); and respiratory increase of 0.74% (95% CI, 0.53 – 0.95).

With regard to gaseous pollutant adjustments, the associations remained significant. Associations were even strong in areas with lower annual mean PM concentrations, and higher annual mean temperatures.

In an editorial accompanying the study, Renee N. Salas, MD, MPH—of the Department of Emergency Medicine at Massachusetts General Hospital and Harvard Medical School—noted the new findings elucidate the well-recognized implication of climate change on cardiovascular and respiratory disease rates.

But it’s in the more newly-discovered associations between climate change and human health—as with chronic disease condition, among others—that drives the call for more education on the real dangers of worsening climate change.

“Neither the gravity and enormity of climate change nor the unfortunate politicization of this health emergency should cause us to shy away from action,” Salas and colleagues wrote. The timeline for action to avert some of the most catastrophic health outcomes of climate change has been estimated to be a little over a decade.”

Liu and colleagues concluded one aspect of health outcomes which must be addressed is the well-evidenced association between PM exposure and worsened cardiovascular and respiratory mortality.

“This study also provides the statistical power to examine the global concentration—response functions of particulate air pollution at both low and high baseline levels,” they noted.

The study, “Ambient Particulate Air Pollution and Daily Mortality in 652 Cities,” was published online in the New England Journal of Medicine.