Even small increases of nitrogen dioxide (NO2) air pollution may cause an uptick in heart- and lung-related deaths, underscoring the need to tighten limits on this type of air pollution, Chinese researchers say.
NO2 is produced by burning fuel for vehicles, power and industrial production. World Health Organization (WHO) air quality guidelines recommend NO2 levels not exceed an annual average of 40 micrograms (one-millionth of a gram) per cubic meter of air (μg/m3).
Many previous studies have reported the harmful health effects of short-term exposure to NO2, but most have been small, covered limited areas, or used different study designs, so results have been inconsistent.
In this study, researchers at Fudan University in Shanghai analyzed daily concentrations of NO2 from 398 cities in 22 low- to high-income countries/regions between 1973 and 2018, along with daily weather data and death records.
The period recorded 62.8 million deaths, including 19.7 million (31.5%) from heart disease and 5.5 million (8.7%) from respiratory issues.
On average, a 10 μg/m3 increase in nitrogen dioxide levels on the previous day was associated with 0.46% increase in total deaths; a 0.37% increase in heart deaths; and 0.47% increase in respiratory deaths.
These associations remained after researchers adjusted for levels of other common air pollutants -- sulfur dioxide, carbon monoxide, ozone and different sizes of fine particulate matter.
In all, 1.23% of deaths across the cities in the study were attributable to nitrogen dioxide, according to findings published March 24 in the BMJ.
While reducing NO2 to zero isn't feasible, the study "provides insight into the public health benefits of substantial NO2 reductions," wrote the authors led by Haidong Kan of Shanghai Key Laboratory of Atmospheric Particle Pollution and Prevention at Fudan University.
Because this was an observational study, it doesn't prove cause and effect. But, the authors wrote, it offers "robust evidence" of links between short-term exposure to NO2 and increased risks of heart and respiratory death, suggesting the need to revise and tighten current air-quality guidelines.
"These findings contribute to a better understanding of how to optimize public health actions and strategies to mitigate air pollution," Kan and his colleagues said in a journal news release.
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SOURCE: BMJ, news release, March 24, 2021