Cardiovascular deaths likely to rise from extreme heat

Climate change due to greenhouse gas emissions is making extreme heat events in the United States more frequent and more intense. This trend is expected to continue over the next several decades. When the body is not able to properly cool itself, dangerous heat-related illnesses, like heat exhaustion or heat stroke, can arise. Extreme heat can also have more subtle, albeit still deadly effects.

The cardiovascular system plays a central role in regulating the body’s temperature. People with cardiovascular disease are at increased risk from extreme heat. An NIH-funded research team led by Dr. Sameed Khatana at the University of Pennsylvania set out to estimate how an increase in extreme heat might affect the rate of cardiovascular deaths.

The researchers analyzed county-level data for the contiguous United States from 2008 to 2019. They compared deaths from cardiovascular disease to the number of summer days with a heat index of at least 90 degrees Fahrenheit. Then they used models of future greenhouse gas emissions and socioeconomic conditions to forecast extreme heat days and county populations during 2036-2065. One model represented a middle-of-the-road scenario. This had moderate population growth and climate policies that limit greenhouse gas emissions and stabilize warming. Another model represented a worst-case scenario, with rapid population growth and greenhouse gas emissions growing unchecked. Their findings appeared in Circulation on October 30, 2023.

More than 12 million adults in the United States died from cardiovascular disease during the summer months of 2008 through 2019. The team estimated that an average of 1,651 (0.2%) of these deaths were associated with extreme heat each year. Under the middle-of-the-road scenario, the team estimated this number would more than double by mid-century, to more than 4,300. Under the worst-case scenario, excess deaths would more than triple, to almost 5,500.

The changes in excess deaths were not even across demographic groups. Excess deaths increased 3.5 times more for people aged 65 and older than for younger adults under the middle-of-the-road scenario. Under the worst-case scenario, excess deaths for elderly adults increased 2.9 times more than for younger adults. For non-Hispanic Black adults, excess deaths increased 4.6 and 3.8 times more than for non-Hispanic White adults.

These results predict a significant increase in cardiovascular deaths due to extreme heat in the U.S. by mid-century. Non-Hispanic Black adults and the elderly may be particularly affected. The increase is due to a combination of more days with a high heat index, aging of the population, and population growth in warmer areas. These findings highlight the need for interventions to help prevent heat-related illnesses.

“The health burdens from extreme heat will continue to grow within the next several decades,” Khatana says. “Due to the unequal impact of extreme heat on different populations, this is also a matter of health equity and could exacerbate health disparities that already exist.”