More Heart Disease Deaths on Very Hot, Very Cold Days

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Dec. 13, 2022 — Extremely hot and extremely cold days are tied to an increase in the risk of death from heart disease, a new study suggests. 

People with heart failure were most at risk when temperatures were extremely hot or cold.

Climate change, which is linked to substantial swings in extreme hot and cold temperatures, is likely a key culprit, according to lead study author Barrak Alahmad, MD, PhD, of the Harvard T.H. Chan School of Public Health in Boston. 

“Investigating the burden of extreme temperatures from now on will enable us to further understand what climate change might hold for cardiovascular risks,” he says. “In this rapidly changing climate and unprecedented pace of warming, it is not the time to be asleep at the wheel.”

No specific temperatures are considered extreme, Alahmad notes. “Heat and cold are context-specific and location-specific.” For example, a 104 F day in Kuwait is a typical summer day, whereas a 104 F day in London resulted in “widespread, incalculable damage.”

For the study, published Dec. 12 in the journal Circulation, the researchers looked at more than 32 million cardiovascular deaths over 4 decades in countries around the world. They compared cardiovascular deaths on the hottest and coldest 2.5% of days in each city with cardiovascular deaths on the days with optimal temperatures. 

The relative risks of death increased gradually for cold temperatures, but somewhat faster for hot temperatures – especially for heart failure, where the risk in extremely hot weather climbed quickly to as much as 12% higher, according to the analysis.

Extremely cold temperatures appeared even more dangerous. They were associated with a 33% greater risk of dying from ischemic heart disease (caused by narrowed arteries); a 32% greater risk of death from ischemic strokes caused by blood clots in the brain; and a 37% greater risk of dying from heart failure. 

Overall, extreme temperatures accounted for 2.2 additional deaths per 1,000 on hot days and 9.1 additional deaths per 1,000 on cold days.

The results were similar even after the researchers adjusted for temperature variability, heatwaves, long-term trends, relative humidity, and air pollutants, including ozone, nitrogen dioxide, and particulate matter.

Protect Your Heart

American Heart Association expert volunteer Nieca Goldberg, MD, medical director of Atria New York and a professor at the New York University School of Medicine in New York City, says everyone needs to take steps to stave off the effects of climate change.  

To protect your heart on extremely hot and cold days, “avoid outdoor activities,” she advises. “If you must go out for an appointment on a very cold day, remember to bundle up, wear gloves, and a hat and a scarf that covers your mouth. Keep your outdoor time to a minimum.” 

“On hot days, do not exercise outdoors, stay indoors as much as possible, and stay hydrated,” she says.

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