Air Pollution Found to Be Possible Cause of Premature Death Rates

Exposure to air pollution is associated with increased respiratory and cardiovascular mortality, according to a study published this week in The New England Journal of Medicine.

The study consisted of data showcasing differing levels of particulate matter (PM) in relation to daily all-cause, cardiovascular, and respiratory mortality rates in 652 cities across 24 countries and regions. PM is an air pollutant that has served as a public health concern due to its toxicity and widespread exposure to humans. Researchers categorized PM in the study by its aerodynamic diameter, in which PM₁₀, deemed inhalable, had a diameter of 10 μm or less and PM_2.5, deemed fine, had a diameter of 2.5 μm or less.

Global estimates were derived from each city’s concentration-response curve through 2 generalized additive models with random-effects meta-analysis to test the association between mortality and air pollution. Researchers tested the impact of an increase of 10 μg per cubic meter in the 2-day moving average of PM₁₀ and PM_2.5 concentration to compare averages over the current and previous day in association to mortality rates.

Data revealed significant associations of PM₁₀ concentration to increases in daily all-cause mortality (0.44%; 95% CI, 0.39 to 0.50), daily cardiovascular mortality (0.36%; 95% CI, 0.30 to 0.43), and daily respiratory mortality (0.47%; 95% CI, 0.35 to 0.58). PM_2.5 concentration similarly exhibited significant associations to daily mortality for all causes (0.68%; 95% CI, 0.59 to 0.77), cardiovascular (0.55%; 95% CI, 0.45 to 0.66), and respiratory (0.74%; 95% CI, 0.53 to 0.95).

Contributing author Yuming Guo, PhD, associate professor at Monash University School of Public Health and Preventative Medicine, stressed in a statement that even low levels of air pollution can increase mortality risk as there is no threshold for associations between PM and death. “Though concentrations of air pollution in Australia are lower than in other countries, the study found that Australians are more sensitive to particulate matter air pollution and cannot effectively resist its adverse impact,” said Guo.

Prior multi-city and multi-country studies have shown comparable results suggesting levels of PM slightly below the current air quality guidelines and standards remain hazardous to public health. As the largest international study to investigate the short-term impact of air pollution on death over a 30-year period, the data invokes a significant association between toxic air pollutants and death rates.

While heightened PM concentrations in areas normally affected by air pollution may raise concern, previously unaffected areas must be monitored due to physiological functions, such as tolerance, which dictates an air pollutant’s impact on mortality risk. In the study, associations between mortality and air pollution were found highest in lower annual mean PM concentrations and higher annual mean temperatures.

A total of 59.6 million deaths from all causes, 20.1 million deaths from cardiovascular disease, and 5.6 million deaths from respiratory disease were accounted for in the study. The strong correlation coefficient of 0.78 between inhalable PM₁₀ and fine PM_2.5 shows a likewise risk for humans as both these air pollutants comparably correlate to gaseous pollutants like nitrogen dioxide, ozone, sulfur dioxide, and carbon monoxide.

“The smaller the airborne particles, the more easily they can penetrate deep into the lungs and absorb more toxic components causing death,” said Guo.

Reference

Liu C, Chen R, Sera F, et al. Ambient Particulate Air Pollution and Daily Mortality in 652 Cities. [published online August 22, 2019]. The New England Journal of Medicine. doi: 10.1056/NEJMoa1817364.