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Risk of death increases with extreme heat and air pollution, study finds

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  • Researchers at the University of Southern California have found that pollution and heat increase the risk of death


  • On days of extreme heat and air pollution, deaths are 21 percent more likely


  • People over the age of 75 are most at risk on days of extreme exposure

The heat waves and the atmospheric pollution are harmful even deadly, and both are expected to increase in frequency due to climate change. A team of researchers at the University of Southern California (United States) has contributed to shedding light on the risks for the Health evaluating six years of data on air quality, temperature and death certificates.

In their work, published in the scientific journal ‘American Journal of Respiratory and Critical Care Medicine’, they have shown that, compared to days without extreme conditions, days of extreme heat carried a 6.1 percent increase in the risk of death. On days of extreme air pollution, deaths were 5 percent more likely. But in the days of extreme heat and air pollutionthe deaths they were a 21 percent more likelya synergistic effect that nearly doubles the impact of the individual exposures combined.

“We found that the effect of exposure to extreme temperatures and extreme pollution on mortality is greater than the sum of their individual effects,” explains Dr. Mostafijur Rahman, lead author of the study.

Previous studies have examined how extreme heat and air pollution separately affect mortality risk, and how each varies with the other. But this study is the first to use a new approach to study what happens when extreme heat and air pollution coincide.

People over 75, who are most at risk

In addition to overall mortality, this study also examined deaths from cardiovascular and respiratory conditions. On days of extreme exposure, lPeople over 75 years old they were the ones that ran higher risk. The findings could ultimately help people, communities and health systems prepare for extreme weather and minimize potential damage.

“Understanding the risks associated with these exposures is really important, because we know that they will increase with climate change in many different parts of the United States and the world,” said Erika Garcia, also lead author of the study.

Forest fires, for example, which are projected to increase by up to 50 percent by the end of the century, often bring extreme heat and pollution that last for days or weeks.

Garcia, Rahman, and their colleagues they studied all deaths occurred in California between 2014 and 2019 (a total of more than 1.5 million) using data from California Department of Public Health death certificates. They also obtained data on air temperature and levels of fine particulate matter (PM2.5), a tiny particulate pollution in the air that is known to cause health problems.

Next, deaths were related to environmental conditions premises based on the person’s address to understand the effects of exposure. Using data on temperature and air pollution levels, the researchers classified each day into one of four categories: no extreme exposure, extreme heat only, extreme air pollution only, or extreme heat and air pollution.

In the days of heat extreme and pollution atmospheric, overall mortality risk increased by 21 percent. The risk of death from cardiovascular problems increased by 29.9 percent and the risk of death from respiratory problems by 38 percent.

Although the researchers did not study the specific causes of death, these problems often include conditions such as heart failure and pneumonia. On days when both heat and air pollution reach extreme levels, people may have more inflammation and oxidative stress, as well as problems regulating their internal body temperature, Rahman says.

Older adults faced a significantly higher risk, with a 36.2 percent increase in the rmortality risk for the older than 75 yearscompared to an 8.5 percent increase in mortality risk for people age 75 and younger when exposed to both extreme heat and pollution.


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