Hot and cold both kill: Extreme temperatures linked to cardiovascular deaths

DALLAS — Mild weather is just what the doctor ordered when it comes to heart health. Noteworthy new research encompassing over 32 million cardiovascular deaths over four decades reports a connection between extreme temperatures, both hot and cold, and higher mortality rates among those with a history of heart disease and problems.

Study authors found there were more cardiovascular deaths on days when temperatures were at their highest or lowest among people with cardiovascular diseases. That includes ischemic heart disease (heart problems caused by narrowed heart arteries), stroke, heart failure, and arrhythmia. Importantly, people with heart failure experienced the most deaths during extreme temperatures.

Extreme temperatures are predicted to become more frequent in the years to come due to climate change. With that in mind, researchers say much more work is necessary to examine and develop new ways to minimize the impact of extreme temperatures on cardiovascular disease and related deaths.

“The decline in cardiovascular death rates since the 1960s is a huge public health success story as cardiologists identified and addressed individual risk factors such as tobacco, physical inactivity, Type 2 diabetes, high blood pressure and others. The current challenge now is the environment and what climate change might hold for us,” says Barrak Alahmad, M.D., M.P.H., Ph.D., research fellow at the Harvard T.H. Chan School of Public Health at Harvard University and a faculty member at the College of Public Health at Kuwait University, in a media release.

Extreme cold can kill more people than heat

Heart disease is the number one cause of death on a global scale. The research team set out to better understand how extreme temperatures may affect heart diseases. To that end, study authors analyzed a massive dataset encompassing over 32 million cardiovascular deaths occurring across 567 cities in 27 countries on five continents between 1979 and 2019. All that data was provided by the Multi-Country Multi-City (MCC) Collaborative Research Network, a consortium of epidemiologists, biostatisticians, and climate scientists collaborating to research the health repercussions of climate and related environmental stressors on death rates.

Climate change, meanwhile, has been linked to substantial swings in extreme hot and cold temperatures by prior studies, prompting researchers to account for both ends of the thermometer during this project. They compared cardiovascular deaths on the hottest and the coldest 2.5 percent of days for each included city with cardiovascular deaths on the days that had an optimal temperature (the temperature linked to the lowest death rates) in the same locations.

For every 1,000 assessed cardiovascular deaths, the analysis found:

  • Extreme hot days accounted for 2.2 additional deaths.
  • Extreme cold days accounted for 9.1 additional deaths.
  • Regarding specific types of heart diseases, the greatest number of additional deaths was found among those with heart failure (2.6 additional deaths on extreme hot days, 12.8 on extreme cold days).

“One in every 100 cardiovascular deaths may be attributed to extreme temperature days, and temperature effects were more pronounced when looking at heart failure deaths,” notes study co-author Haitham Khraishah, M.D., a cardiovascular disease fellow at the University of Maryland School of Medicine and the University of Maryland Medical Center in Baltimore. “While we do not know the reason, this may be explained by the progressive nature of heart failure as a disease, rendering patients susceptible to temperature effects. This is an important finding since one out of four people with heart failure are readmitted to the hospital within 30 days of discharge, and only 20% of patients with heart failure survive 10 years after diagnosis.”

How can people avoid extreme weather?

Researchers theorize that targeted warning systems and advice geared toward vulnerable people may help prevent cardiovascular deaths during very hot or cold days.

“We need to be on top of emerging environmental exposures. I call upon the professional cardiology organizations to commission guidelines and scientific statements on the intersection of extreme temperatures and cardiovascular health. In such statements, we may provide more direction to health care professionals, as well as identify clinical data gaps and future priorities for research,” Dr. Alahmad adds.

While this project covered a lot of ground, areas including South Asia, the Middle East, and Africa were underrepresented in the data. As such, study authors say this project should not be used to make global estimates about the impact of extreme temperatures on cardiovascular deaths.

“This study contributes important information to the ongoing societal discussions regarding the relationship between climate and human health. More work is needed to better define these relationships in a world facing climate changes across the globe in the years ahead, especially as to how those environmental changes might impact the world’s leading cause of death and disability, heart disease,” concludes AHA Past President Robert A. Harrington, M.D., FAHA, who is the Arthur L. Bloomfield Professor of Medicine and chair of the department of medicine at Stanford University.

The study is published in the journal Circulation.

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