Nov. 30, 2021 -- When skies were blue and air pollution was reduced during stay-at-home lockdowns at the beginning of the COVID-19 pandemic, there were fewer severe heart attacks in the United States, a new study suggests.

The researchers examined air pollution levels and numbers of severe heart attacks reported by emergency medical service personnel in 29 U.S. states, from January 2019 through April 2020.

This included about 2 weeks when many states issued stay-at-home orders after the World Health Organization declared that COVID-19 was a pandemic in March 2020.

During lockdowns, there were hardly any vehicles on the roads or planes in the skies, so exhaust emissions plummeted.

More specifically, there were fewer tiny particles in the air -- also called particulate matter -- that are less than 2.5 micrometers wide.

In this study, each 10 µg/m3 drop in levels of this size of particulate matter was associated with a 6% reduction in severe heart attacks, after correcting for the census district, day of the week, month, and year. (The term “µg/m3” refers to the concentration of air pollutants. It stands for micrograms, or one-millionth of a gram, per cubic meter of air.)

The findings were presented by Sidney Aung, a fourth-year medical student at the University of California, San Francisco, and colleagues at the American Heart Association (AHA) 2021 Scientific Sessions.

The pandemic-related shutdown was "a unique opportunity" to investigate how a short period of cleaner air might be associated with fewer severe heart attacks, senior author Gregory M. Marcus, MD, a professor at the University of California, San Francisco, tells WebMD.

"And, indeed, as pollution fell, we found a concomitant reduction in the most serious forms of heart attack," he says.

But the researchers caution that this was a preliminary observational study, so it cannot show cause and effect. And while air pollution may have been a contributing factor, other things may explain the observed decrease in heart attacks.

Nevertheless, these findings show "the possible immediate health impacts of pollution," so people should push for cleaner air initiatives, Aung tells WebMD.

This study "is perhaps one of the few in the United States suggesting a reduction in [heart attacks] as a consequence of COVID-19-related reduction in air pollution levels," says Sanjay Rajagopalan, MD, who was not involved with this research.

The results "clearly suggest that urgent action is needed to switch from fossil fuel energy sources to clean energy sources," to benefit people's health as well as the planet, says Rajagopalan, a professor at Case Western Reserve University in Cleveland, OH.

"If these results hold up, it reinforces the benefits of air pollution reduction, as a cost-effective way to improve health,” says Joel D. Kaufman, MD, a professor at the University of Washington in Seattle who was not involved with this research.

"It also means that reducing fossil fuel combustion, which we need to do anyway to combat climate change, might mean tremendous health benefits now, even if the climate benefits take a few years to accrue."

Show Sources

American Heart Association Scientific Sessions: “Pandemic-Related Diminished Pollution and ST-elevation Myocardial Infarctions.”

Sidney Aung, fourth-year medical student, University of California, San Francisco.

Gregory M. Marcus, MD, professor, University of California, San Francisco.

Sanjay Rajagopalan, MD, professor, Case Western Reserve University, Cleveland, OH.

Joel D. Kaufman, MD, professor, University of Washington, Seattle.

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