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The number of cardiovascular deaths from extreme heat could more than double in the United States – and possibly triple – by the middle of the century if more isn't done to reduce greenhouse gas emissions that contribute to climate change, new research suggests.

Older adults and non-Hispanic Black adults may be especially at risk, according to the published Monday in the ·¬ÇÑÊÓƵ journal Circulation.

"Climate change and its many manifestations will play an increasingly important role on the health of communities around the world in the coming decades," Dr. Sameed Khatana, the study's lead author, said in a . Khatana is an assistant professor of medicine at the University of Pennsylvania and a cardiologist at the Philadelphia VA Medical Center. "Climate change is also a health equity issue as it will impact certain individuals and populations to a disproportionate degree and may exacerbate preexisting health disparities in the U.S."

Extreme heat – a maximum heat index of 90 degrees Fahrenheit or higher – was associated with 1,651 excess cardiovascular deaths per year from 2008 to 2019, according to the analysis, funded by the AHA and the National Heart, Lung, and Blood Institute. By midcentury, that could rise to 4,320 excess deaths a year if proposed policies to reduce greenhouse gas emissions are implemented. A projected 5,491 of such deaths may occur if only minimal action is taken.

For that reason, how much and how quickly emissions policies are adopted nationwide could determine how many lives will be lost due to extreme heat, Khatana said.

Researchers said the extreme heat also will exacerbate preexisting health disparities. The increase in heat-related cardiovascular deaths is projected to be up to 3.5 times greater in people 65 and older compared to younger adults, the study found. For Black adults, such deaths could be up to 4.6 times greater than for white adults.

"Previous studies have suggested Black residents may have less access to air conditioning; less tree cover; and a higher degree of the 'urban heat island effect' – built-up areas having a greater increase in temperature than surrounding less-developed areas," Khatana said.

Also, the social isolation experienced by some older adults has previously been linked with a higher probability of death from extreme heat, he said.

Yet, however alarming the projections from this study may be, they are likely "conservative," Dr. Robert Brook said in the release. He is executive director of cardiovascular prevention at Wayne State University School of Medicine in Detroit.

That's because the study only focuses on cardiovascular deaths due to intense heat, said Brook, who was not involved with the new research. It doesn't include nonfatal heart attacks, strokes and heart failure hospitalizations, which also may be linked to extreme heat days, he said.

"The full extent of the public health threat, even just due to cardiovascular death, is likely much greater than presented in the study," Brook said.