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• Posted October 30, 2023

U.S. Heat-Related Heart Deaths Will Multiply With Warming Temperatures

As sweltering summer days become more common, the number of Americans who die of heat-related heart problems or strokes could soar over the next few decades, a new study projects.

The study -- published Oct. 30 in the journal Circulation -- estimates that by mid-century the United States will see those preventable deaths more than triple if greenhouse gas emissions are allowed to rise unchecked.

Older adults and Black Americans are expected to be hardest-hit -- a prospect that would widen the racial disparities in heart disease that already exist.

That's the bad news. The more hopeful finding is that some of those heat-related deaths could be avoided by implementing current proposals on cutting emissions.

"Our study suggests there could be a benefit from reducing emissions, and within a short time frame," said lead researcher Dr. Sameed Khatana, a cardiologist and assistant professor of medicine at the University of Pennsylvania.

Experts have long known that heat waves often trigger a spike in strokes, heart attacks and other cardiovascular complications -- typically among people with preexisting risk factors.

That's because the heart and blood vessels (cardiovascular system) are central players in regulating body temperature, Khatana said. When the body overheats, the heart works harder, pumping blood to the periphery of the body to release heat through sweat.

And for vulnerable people, that stress can be too much.

"We also know the number of extreme heat days is projected to increase," Khatana said.

That fact, coupled with an aging population and more Americans moving to hotter parts of the country, points to an obvious scenario: an increase in heat-related cardiovascular deaths.

To get a handle on what that future could hold, Khatana's team first looked at data on cardiovascular deaths and extreme heat days in U.S. counties between 2008 and 2019. "Extreme" meant days where it felt like 90 degrees or more.

During those years, the researchers estimate, extreme heat caused an average of 1,651 "excess" cardiovascular deaths per year -- that is, deaths that would not have happened without those temperature extremes.

The researchers then used those figures, along with estimates on environmental and population changes, to make projections about the next few decades -- 2036 to 2065. And the picture was not pretty.

Under a more positive scenario, in which greenhouse gas emissions were moderately curtailed, heat-related cardiovascular deaths would still rise -- more than doubling, to an average of 4,320 per year.

In part, that's because extremely hot days would increase, from 54 days annually in recent years, to 71 days.

But that outlook was better than the second scenario the researchers analyzed, in which "nothing" was done to curb emissions, Khatana said.

In that case, Americans would typically face roasting temperatures 80 days per year. And heat-related cardiovascular deaths would more than triple, to 5,491 per year nationwide.

All of those figures, though, are likely underestimates, according to Kristina Dahl, a principal climate scientist with the nonprofit Union of Concerned Scientists.

Heat-related deaths, she said, are not formally tracked by public health agencies, nor are they necessarily recognized as such on death records.

Extreme heat is, in fact, considered a "silent killer," said Dahl, who was not involved in the study. Although they are often deadly, she noted, heat waves do not grab the headlines that hurricanes and similar disasters do.

The good news, Dahl said, is that temperature responds quickly to changes in greenhouse gas emissions.

So as this study projects, she said, curbing emissions should help limit extreme heat days, and heart-related deaths, in relatively short order.

The study also found that Black Americans would be especially hard-hit by increases in extreme heat: Compared with white Americans, they could see an almost fivefold increase in heat-related cardiovascular deaths.

One reason, Khatana and Dahl said, is that Black Americans are more exposed to the ravages of sweltering temperatures.

Compared with white Americans, they are more likely to live in big cities -- where concrete traps heat and many apartment dwellers lack air conditioning. Plus, Dahl said, many people of color are exposed to heat extremes through jobs that keep them outdoors.

"Water, shade and rest" are key to protecting those workers, Dahl said. But as of now, she added, only three U.S. states have set standards on that issue.

Both experts pointed to measures that communities can take to protect vulnerable residents: planting trees in urban neighborhoods to provide shade; creating "cooling centers" that are accessible, safe and appealing enough to attract people; and devising "heat action plans" to prepare for heat waves.

Khatana made another point: This study looked only at heat-related deaths. Many other Americans suffer non-fatal cardiovascular complications during heat waves -- serious enough to send them to the hospital and have lasting effects on their health and quality of life.

"Cardiovascular deaths are just the tip of the iceberg," Khatana said.

More Information

The U.S. Centers for Disease Control and Prevention has more on extreme heat.

SOURCES: Sameed Khatana, MD, MPH, assistant professor, medicine, Perelman School of Medicine, University of Pennsylvania, and staff cardiologist, Philadelphia Veterans Affairs Medical Center, Philadelphia; Kristina Dahl, PhD, principal climate scientist, Union of Concerned Scientists, Cambridge, Mass.; Circulation, Oct. 30, 2023, online