(Reuters Health) - People who live in cities where the air is polluted by factories and traffic fumes may not live as long as they would have with cleaner air, a recent study suggests.

FILE PHOTO: Buildings stand shrouded in smog in Mexico City, March 16, 2016. REUTERS/Edgard Garrido

Researchers focused on ozone, an unstable form of oxygen produced when various types of traffic and industrial pollution react with sunlight. Worldwide, about four in five people in urban areas are exposed to ozone levels that exceed safe levels recommended by the World Health Organization, the study team notes in The BMJ.

The study looked at ozone levels and deaths in 406 cities in 20 countries around the world. It found that overall, about 6,000 deaths a year in those cities could be prevented if stricter air quality standards reduced ozone levels below the WHO-recommended maximum of 100 micrograms per cubic meter of air (mcg/m3).

“Our study confirms the evidence from previous studies on the adverse health impacts associated to the exposure to ground-level ozone,” said lead study author Ana Maria Vicedo-Cabrera of the University of Bern in Switzerland.

“Patients should be aware of the risks of the exposure to high levels of ozone, in particular when their health is already compromised,” Videco-Cabrera said by email.

Air pollution has long been linked to higher risks of heart attacks, strokes, asthma attacks and other respiratory problems with the potential to shorten people’s lifespan. Less is known, however, about how much exposure to ozone levels higher than WHO limits might directly impact longevity, the study team notes.

In the current study, researchers examined data on ozone levels and more than 45 million deaths between 1985 and 2015.

On average, a 10 mcg/m3 increase in ozone during the current and previous day was associated with a 0.18% increased risk of death, the study team found.

Even when cities had ozone concentrations below WHO limits, levels between 70mcg/m3 and 100mcg/m3 were still associated with an increased risk of death during the study period. This suggests that even stricter air quality standards might be needed, the study team concludes.

The study wasn’t designed to determine whether or how ozone exposure might cause premature deaths.

The researchers also didn’t have enough data from certain regions of the world, including South America, Africa, and the Middle East, to craft a truly global estimate of how ozone exposure impacts longevity. The ozone assessment also didn’t look at outdoor versus indoor air quality.

“We don’t fully understand the entire pathway from ozone exposure to mortality,” said Dr. Frank Gilliland, a researcher at the University of Southern California in Los Angeles who wasn’t involved in the study.

“We do know that ozone is a toxic gas that produces airway and systemic oxidative damage and inflammation when inhaled these adverse effects are likely to have large impacts on those with health problems such as respiratory conditions or who are frail from aging,” Gilliland said by email.

SOURCE: bit.ly/2UKNecD The BMJ, online February 10, 2020.