When it’s hot outside, your heart has to work harder to keep your body cool. This puts extra pressure on your heart and blood vessels.
For people who already have heart problems, this extra stress can lead to a heart attack or stroke.
A new study from Tulane University shows that the danger becomes much worse when the air is both hot and humid. The study found that people are six times more likely to go to the emergency room for a heart-related problem on extremely hot and humid days.
The researchers looked at over 340,000 emergency room visits in Dhaka, Bangladesh, a city known for its intense heat and humidity. They compared the number of visits between 2014 and 2019 with historical weather data.
They found that on low-humidity days, high heat alone increased the risk of a heart emergency by 4.4%. But on the most humid days, when the relative humidity was over 82%, the risk jumped by 26.7%.
“This is a big deal,” said lead author Mostafijur Rahman from Tulane University. “We already knew heat was a problem, but I didn’t expect humidity to make the risk so much higher.”
The study found no major risk from humidity alone. But when it’s both hot and humid, sweat doesn’t evaporate as easily, which makes it harder for the body to cool down. This forces the heart to pump even harder, increasing the risk of a serious health problem.
High heat was defined as temperatures above 84 degrees Fahrenheit. On those hot days, there was an 8% increase in heart-related emergencies. But when humidity rose above 80%, the risk went up even more—and this was true for all age and gender groups.
This research is especially important for places like Dhaka, where few people have air conditioning and the country is very vulnerable to climate change. Rising global temperatures mean more people will be exposed to dangerous heat and humidity.
“There are billions of people in places like Southeast Asia and Africa who are feeling the effects of rising temperatures, but don’t have access to air conditioning,” said Rahman. “We hope this study encourages governments to build early warning systems for heat and humidity.”
Rahman also gave tips for staying safe in hot weather: drink plenty of water, stay indoors if you can, wear light and breathable clothing, and visit places with air conditioning like shopping malls or libraries.
If you care about heart health, please read studies that Manganese can help clear arterial plaques and treat heart disease and Aspirin use linked to heart failure.
For more about heart health, please read studies about the blood thinner drug that can prevent strokes in people with hidden heart issues and new guidelines on daily aspirin for heart attack and stroke prevention.
The study is published in Science of the Total Environment.
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