Short-term exposure to nitrogen dioxide may increase risk for CV, respiratory mortality

Even small increases in nitrogen dioxide in the air may increase the risk for cardiovascular and respiratory mortality, according to new data published in The BMJ.

Researchers evaluated health and environmental data from the Multi-City Multi-Country database to assess locations with available ground level nitrogen dioxide measurements. The multilocation study included 398 cities located in 22 low- to high-income countries/regions. From 1973 to 2018, there were 62.8 million deaths from total or non-external causes; of those, 19.7 million were deaths from CV diseases and 5.5 million were deaths from respiratory diseases.

The median annual nitrogen dioxide concentration was 26.9 µg/m³. According to the researchers, the median concentration is lower than the WHO’s air quality guidelines for nitrogen dioxide (40 µg/m³).

The primary outcome measure was daily deaths from total CV and respiratory causes from 1973 to 2018. For every 10 µg/m³ increase in nitrogen dioxide concentration in the previous day, researchers observed a 0.46% (95% CI, 0.36-0.57) increase in total mortality, 0.37% (95% CI, 0.22-0.51) increase in CV mortality and 0.47% (95% CI, 0.21-0.72) increase in respiratory mortality. These associations persisted after the researchers adjusted for co-pollutants such as particulate matter, ozone, sulfur dioxide and carbon monoxide.

In other results, the proportion of deaths attributable to nitrogen dioxide concentration above the counterfactual zero level was 1.23% (95% CI, 0.96-1.51), according to the researchers.

“We found robust associations of NO₂ with daily mortality from total, cardiovascular and respiratory exposures to other air pollutants. More importantly, we pooled a concentration-response curve for NO₂ at the global level, suggesting an almost linear association, with no discernible thresholds. This result suggests that NO₂ is associated with considerable health risks even at levels below health-based standards and guidelines, including the current WHO air quality guidelines,” Xia Meng, PhD, research associate at the School of Public Health at the Key Laboratory of Public Health Safety of the Ministry of Education and Key Laboratory of Health Technology Assessment of the Ministry of Health at Fudan University in Shanghai, and colleagues wrote.

The researchers concluded that these data “contribute to a better understanding of how to optimize public health actions and strategies to mitigate air pollution.”