Hot and cold: Climate changes can affect heart health

Cardiovascular disease is the leading cause of death around the world. And both extreme hot and extreme cold can increase the risk of dying for people with cardiovascular disease, especially those with heart failure. Recent research has found that exposure to severe temperatures increases the risk of dying from common heart-related problems. Understanding the connection between cardiovascular disease and the extreme weather shifts associated with a changing climate can help researchers and medical professionals work together to better protect people's heart health in the years ahead.

In a study published in December 2022 in the American Heart Association journal Circulation, researchers studied cardiovascular-related deaths during the hottest and coldest days between 1979 and 2019. The team analyzed 32 million cardiovascular-related deaths across 27 countries over 40 years, comparing death rates on extreme days in 567 cities to rates on normal temperature days in the same cities for people with various heart diseases, including heart attack, stroke, heart failure and arrhythmia.

The study showed 2.2 additional deaths for every 1,000 cardiovascular deaths recorded on the hottest days. And extremely cold temperatures carried a higher risk: 9.1 deaths for every 1,000 cardiovascular-related fatalities. Of the heart conditions studied, heart failure showed the strongest link to extreme temperatures. Those with heart failure experienced 2.6 more deaths on the hottest days and a significant 12.8 additional deaths during extremely cold days, compared to the general population.

According to study co-author Dr. Haitham Khraishah, a cardiovascular disease fellow at the University of Maryland Medical Center in Baltimore, about 1 out of every 100 cardiovascular deaths could be linked to days of extreme temperatures. This connection grows stronger when considering deaths from heart failure, specifically.

"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," he says. "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."

Efforts to identify and address risk factors such as tobacco use, physical inactivity, Type 2 diabetes and high blood pressure have led to a significant decline in cardiovascular death rates since the 1960s, according to the study’s lead author Dr. Barrak Alahmad. "The current challenge is the environment and what climate change might hold for us.” Alahmad is a research fellow at the Harvard T.H. Chan School of Public Health at Harvard University in Boston and a faculty member at the College of Public Health at Kuwait University in Kuwait City.

To prevent heart-related deaths during very hot or cold weather, the researchers suggest making warning systems and giving advice to people who are more at risk. "We need to be on top of emerging environmental exposures," said Alahmad. He encourages cardiology groups to create guidelines and scientific statements about how extreme temperatures affect heart 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."

Previous research on temperature-related deaths has been limited in location and mostly looked at total cardiovascular deaths, not specific causes. However, the data used for this study underrepresent South Asia, the Middle East and Africa, making it difficult to formulate estimates of how extreme temperatures are affecting cardiovascular deaths around the world. To better understand the reasons behind temperature-related deaths, future research could dig deeper into how the factors that contribute to the increased risk — such as air quality, lifestyle choices, and access to medical care — interact with extreme temperatures to impact heart health.

Still, Dr. Robert A. Harrington, chair of the Department of Medicine at Stanford University in California who was not involved in the study, says the research contributes greatly to discussions about the relationship between climate change and human health. However, Harrington says, "more work is needed to better define these relationships in a world facing climate changes across the globe in the years ahead."