Extreme temperatures could result in more heart-related deaths

Temperature extremes—both excessive heat and frigid conditions—can increase health risks for people with heart disease, such as narrowed arteries, stroke, and arrhythmia. Scientists warn that heart failure is linked to the greatest number of additional deaths from extreme temperature swings, and these risks could escalate as climate change results in more severe weather events.

“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,” said Barrak Alahmad, MD, MPH, PhD, 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, in a December 2022 news release from the American Heart Association (AHA). "The current challenge now is the environment and what climate change might hold for us."

Researchers conducted a multinational analysis of more than 32 million heart-related deaths that occurred in 27 countries across five continents between 1979 and 2019. The 2022 analysis published in Circulation compared cardiovascular deaths that occurred on the hottest and the coldest 2.5 percent of days in 567 different cities during this 40-year period with heart-related deaths that occurred on days with ideal temperatures, or mild weather that is associated with the lowest death rates.

For every 1,000 heart-related deaths, the analysis found that:

• Extreme cold days accounted for 9.1 additional deaths.
• Extreme hot days accounted for 2.2 additional deaths.
• People with heart failure accounted for the greatest number of additional deaths (12.8 more deaths on extreme cold days and 2.6 additional deaths on extreme hot 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,” said the study’s co-author, Haitham Khraishah, MD, a cardiovascular disease fellow at the University of Maryland School of Medicine and the University of Maryland Medical Center in Baltimore.

How extreme weather may tax the heart

It’s unclear why very hot or very cold weather is tied to more heart-related deaths. Scientists are still working to understand this link. “There are a lot of different theories,” says Benjamin Yang, MD, a cardiologist at Sky Ridge Medical Center in Lone Tree, Colorado. “But no one is absolutely sure why it happens.”

“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,” Dr. Khraishah noted.

An earlier October 2018 study published in JAMA Cardiology looked at data from 274,029 Swedish older adults who experienced heart attacks between 1998 and 2013. The average age of these participants was 72 years old. Researchers compared the date of each heart attack and location of every patient to the weather reported on that day. They found that cardiac risks were greatest when the temperature dropped below 32 degrees Fahrenheit. Risks decreased by 3 percent with each 13-degree increase. Lower air pressure, fewer hours of sunshine, and strong winds were also associated with an increase in risk.

Frigid temperatures cause blood vessels to narrow, which increases blood pressure. A spike in blood pressure may, in turn, increase a person’s risk of heart attack or stroke—especially if they have other heart-related risk factors, such as obesity, high cholesterol, or diabetes.

A combination of low temperatures and overexertion, like shoveling snow, which requires more oxygen to be delivered to the heart, can also increase heart attack and stroke risks. A February 2017 study published in the Canadian Medical Association Journal suggests that heart attack risks in men may increase the day after heavy snowfall.

Holiday stress and seasonal depression may contribute to these heart-related risks. “Depression has a strong correlation with a lot of myocardial infarctions,” Dr. Yang says. “An increased amount of stress means you have an increased risk of having a heart attack."

Other theories include lack of exercise and an unhealthy diet during the winter months, along with excess drinking during the holiday season, which puts extra stress on the heart.

On the flip side, heat waves can lead to heat-related illnesses, such as heat cramps, heat exhaustion—and in the most extreme cases, heat stroke. Extreme heat can also exacerbate existing chronic health issues, such as diabetes. It’s also linked to heart or respiratory conditions since high temperatures are often associated with higher levels of dangerous air pollutants.

Know the warning signs

In the United States, heart disease is the leading cause of death among adults across most racial and ethnic groups. In 2021 alone, it claimed roughly 695,000 lives, or accounted for about 1 in every 5 deaths, according to the Centers for Disease Control and Prevention (CDC).

It’s important to recognize the symptoms of stroke and heart attack and get immediate medical attention. Symptoms vary from one person to the next, but stroke warning signs include:

• Sudden loss of vision in one or both eyes
• Sudden balance issues or trouble walking
• Numbness or weakness of limbs on one side of the body
• Drooping of the face on one side only
• Sudden difficulty speaking or confusion
• A severe headache

Signs of a heart attack include:

• Chest discomfort that lasts more than a few minutes, but that may go away and then return
• Pain or discomfort in one or both arms, back, neck, or jaw
• Shortness of breath, with or without chest pain or pressure
• Cold sweat, nausea, or lightheadedness

Protect your heart health

Taking certain weather-related precautions on extremely hot or cold days can help mitigate potentially harmful effects on the heart. This may include staying indoors in climate-controlled conditions, wearing clothes that can help the body stay warm or cool off, taking all medications as prescribed by your healthcare provider (HCP), and staying well-hydrated. But heart disease prevention and management are year-round commitments, Yang points out.

Following a heart-healthy diet that emphasizes fruits and vegetables, whole grains, and lean protein—while limiting salt, sugar and saturated fats is key. Getting regular exercise, being aware of your numbers—cholesterol, blood pressure, and blood sugar—and keeping these levels in a healthy range can help your protect your heart health.