Heart-Related Deaths More Likely During Day/Night Heatwaves

More people die from heart problems during heatwaves where high temperatures stretch through both the day and night, a new study says.

Heatwaves that offer no relief at night — known as compound heatwaves — are much more deadly than soaring daytime temperatures alone, researchers reported April 1 in the Journal of the American College of Cardiology.

People are 86% more likely to die from a heart-related condition during a compound heatwave, compared to a 19% increased risk from daytime-only heatwaves and 16% from nighttime-only heatwaves, researchers said.

“Traditional heatwave definitions fail to capture the full scope of these risks,” senior researcher Renjie Chen, a professor at Fudan University School of Public Health in Shanghai, China, said in a news release.

For the study, researchers analyzed data for nearly 2.4 million heart disease deaths that occurred in mainland China from 2013 to 2019, comparing them to hourly temperatures.

Results showed that risk of heart-related death increases steadily during a compound heatwave, while risk tends to peak and then decline during daytime or nighttime heatwaves.

People were particularly more likely to die from sudden cardiac arrest, heart attack and heart failure during a compound heatwave, researchers found.

For example, compound heatwaves brought an 86% increased risk of death from sudden cardiac arrest, compared with a 37% increased risk from nighttime and 24% increased risk of daytime heatwaves.

Likewise, heart attack deaths were 88% more likely during a compound heatwave versus 16% during a nighttime and 13% during a daytime heatwave.

And heart failure deaths were 97% more likely in a compound heatwave, but just 24% more likely in either a daytime or nighttime heatwave.

These results show that more effort needs to be put on protecting people from continual heat, such as providing cooling shelters in cities and improving climate control in homes, researchers said.

“Given the increasing frequency and intensity of compound heatwaves due to climate change, our findings highlight the need for disease-specific prevention strategies and revised public health guidelines to better protect at-risk populations,” Chen said.

Researchers next plan to project how many people are likely to die from heatwave-related heart problems under different climate change scenarios.

More information

Harvard Medical School has more on heart problems and heatwaves.

SOURCES: American College of Cardiology, news release, April 1, 2025; Journal of the American College of Cardiology, April 8, 2025

Source: HealthDay