Short-term exposure to three common air pollutants may increase the risk of dying from asthma, according to new research published online in the American Thoracic Society’s American Journal of Respiratory and Critical Care Medicine.

In “Short-Term Exposure to Ambient Air Pollution and Asthma Mortality,” Yuewei Liu, PhD, and Chinese co-authors report that short-term exposures to higher levels of fine particulate matter (PM2.5), particles so small they are invisible to the eye; nitrogen dioxide (NO2); and ground-level ozone (O3), commonly referred to as smog; appeared to increase the chances of an asthma death.

The authors did not find a link between asthma deaths and higher levels of three other air pollutants know to worsen respiratory problems, including particulate matter (PM10), particles larger than PM2.5but still no bigger than one-sixth the width of a human hair; sulfur dioxide (SO2); and carbon monoxide (CO).

Previous studies have linked short-term exposure to air pollution to an increased risk of asthma symptoms, asthma exacerbations and emergency department visits and hospital admissions due to asthma.

“However, the association between air pollution and asthma death remains less clear,” said Dr. Liu, lead study author and associate professor in the School of Public Health at Sun Yat-sen University.

“Given that short-term exposure to air pollution has been associated with increased risk of deaths from a variety of causes, including chronic obstructive pulmonary disease, or COPD, we hypothesized that air pollution might also increase the risk of death from asthma.”

The researchers analyzed the death certificate data of 4,454 people in China’s Hubei province who died from asthma between 2013 and 2018. The province has a population of about 59 million people, and more than 50 air quality monitoring stations.

Air pollutant exposures were estimated for homes within 50 kilometers of a monitoring station using “inverse distance weighted averages,” which gave greater weight to those addresses closest to the monitoring stations. The researchers used a “time-stratified case-crossover design” that compared air pollution levels on the day a person died to air pollution levels on three or four “control days,” which were the same weekdays within the same month as the case day.

The study found that the odds of dying from asthma increased by:

  • 3% for each 10 micrograms per cubic meter (?g/m3) increase in PM2.5 exposure
  • 1% for each 10 ?g/m3 increase in NO2 exposure
  • 6% for each 10 ?g/m3 increase in O3 exposure

The researchers adjusted findings for daily mean temperature and relative humidity, which may have biased results, on the days analyzed. However, unknown factors such as allergens or medication use could have affected their study, and the researchers cautioned against applying their results to other populations, “especially those with much lower air pollution exposures.”

“Our findings provide new evidence that short-term exposure to air pollution may increase the risk of dying from asthma and highlight the need for those with asthma to take effective measures ? staying indoors with an air purifier or wearing a mask ? to reduce air pollution exposures when those levels are very high,” Dr. Liu said.