July 21, 2023 – Richard Carter had spent the morning walking the picket line outside the Walt Disney Studios in Burbank, CA, with other striking actors. Now, at noon, the temperature had reached 93 F, with a hot breeze blowing. Yet Carter, a 50-something background actor who counts the television show This is Us among his credits, was still cheerful.
Some might call him an “iguana,” one of those people who, like the reptiles that prefer to bask in 95 degrees, don’t complain when the temperatures skyrocket. He notices but doesn’t dwell.
“I say, ‘Damn, it’s hot,’” he said, then quickly adds, “I’d rather say that than ‘Damn, it’s cold.’”
A transplant from Chicago, he can still describe in detail that sub-20-degree day long ago – with a wind chill that he said made it feel like 60 below – as he waited for a bus that was 20 minutes late. That’s when he and his wife decided to pack up and head west. “It didn’t feel that bad today,” he said of the 90 F-plus heat.
In Bend, OR, temperatures are toasty, too, reaching the mid-90s. Yet, the weather hasn’t stopped Patrick Fink, MD, 35, an emergency medicine doctor and wilderness medicine specialist at St. Charles Health System, from getting in a couple of hours on his mountain bike regularly. “I don’t mind it, and I have no problem exercising in it,” he said. “I think it’s a matter of serial exposure.”
This summer, the heat is on, and it’s been hard for most of us not to notice. As of July 20, more than 100 million Americans were under heat alerts, according to the National Integrated Heat Health Information System, a collaboration of federal partners to provide information on the risks of extreme heat. Cities that are typically hot, like Phoenix, are setting records this summer, on July 20 hitting 110 F degrees for 21 consecutive days. The world ended the hottest week on record July 10, according to the World Meteorological Association. And there’s more heat – much more – to come, experts warn.
With extreme heat in the forecast, learning to cope in the heat is the new gotta-have skill. “I think we all have to learn to live with it,” Fink said, “because it isn’t going to change anytime soon.”
But is handling the heat a skill, or is it all genetics? Are some people just able to cope with sizzling temperatures, while some can't? It’s debated among experts, with some saying people may tend to have a better or worse tolerance to heat.
Genetics or Not?
Heat tolerance is likely is partly genetic, said Thomas E. Bernard, PhD, a professor of public health at the University of South Florida in Tampa, who studies occupational health and heat stress. Just as some people have higher natural athletic skills than others, some of us are better physically able to withstand high temperatures, he said. But just as sports training can help athletes of any ability compete better in their sports, improving aerobic fitness can help improve heat tolerance, he said.
Here’s why. “Heat stress is not so much a hot environment, but that you generate heat inside your body,” Bernard said, and for you to cool down, that heat must get out. Someone who is aerobically fit also has good cardiovascular capacity and can dissipate that heat out to the environment better, he said.
Genetics likely does not have a large role in heat tolerance, said Graham M. Brant-Zawadzki, MD, an assistant professor of emergency medicine and wilderness medicine specialist at the University of Utah Hospitals and Clinics in Salt Lake City. Many other things do affect heat tolerance, he said.
Being overweight or obese, with the extra layer of insulation, can make people less heat tolerant. Diabetes can damage blood vessels and nerves, affecting sweat glands and the body’s ability to cool. Certain medications, including blood pressure medicine such as diuretics, antihistamines, and psychiatric medication, can affect heat tolerance. Age plays a role in heat tolerance, with infants, young children, and older adults more likely to struggle with heat, Brant-Zawadzki said.
But, he said, “we are all capable of becoming more heat-tolerant relative to our own baseline.”
How to Train and Adapt
Regularly being active in the heat can be key to tolerating it, said Fink, the mountain-biking emergency medicine doctor. “I do think I am heat-acclimated because I do it regularly,” he said.
Training in the heat builds tolerance, agreed Brant-Zawadzki. Do it judiciously and with your doctor’s OK, he said.
“The idea is to stress yourself for about 20 minutes at a time, and then give yourself 10 minutes to cool down.”
Do that a few times a day. This, he said, causes a response on a cellular level, with the body producing more of what experts call “heat shock” proteins. “Producing more of these proteins help drive some of the changes that help people deal better in the heat,” Brant-Zawadzki said.
Those with higher levels of these proteins hyperventilate less, for instance, he said.
The CDC and the National Institute for Occupational Safety and Health call heat acclimatization “the improvement in heat tolerance that comes from gradually increasing the intensity or duration of work performed in a hot setting.” For employers hoping to keep workers from getting heat-related illness, the agencies offer a schedule. Workers increase the amount of time working in the heat gradually, working up to 100%.
“The heat exposure and the physical exertion have to occur at the same time,” Bernard said. As you acclimate, “you start to sweat earlier, sweat more, and lose less salt.”
Simple Strategy: Turn Down That Air Conditioning
“One thing we can [also] do is decrease the level of air conditioning we use,” Brant-Zawadzki said. “It limits our ability to acclimate ourselves.” It’s typical for people to go from a very hot 105 degrees outside to a restaurant that could be as chilly as 65 degrees, he said. That won’t help boost tolerance to heat.
As a general goal, he suggests keeping the house or office air conditioner set at no more than 10 degrees cooler than outside. Of course, if it’s 100 degrees out, keeping the air conditioner at 90 degrees won’t be helpful. But try not to set the air conditioner 20 or 30 degrees colder than outside, he said.
What About Supplements?
Researchers are looking at the role of the supplement betaine, also called trimethylglycine, to improve heat tolerance. So far, it seems to help in animal studies, said Brandon Willingham, PhD, a registered dietitian and assistant professor of kinesiology at Coastal Carolina University in Conway, SC, who did the research while at Florida State University. It may act in a similar way as the heat shock proteins, he said.
But there is not yet evidence that it works in people, although research is continuing. “Maybe in a year, we’ll have a different story to tell,” he said.
Conner Ohlau, 41, of Scottsdale, AZ, works as a project manager for a commercial construction company. “I’m a project manager who works with my hands,” he said, preferring outside work to days at a desk and computer. One day recently, he had worked outside from 10 until 5, with the temperature reaching 117 F. He said people often can’t believe he works day in and day out in the intense heat.
He’s learned how to handle the heat. “I keep the sun off me, that’s the key,” he said, wearing a hat and neck covers when the sun gets intense. “When you’re outside, you have to be able to put something cool on your neck every 15-20 minutes.” He also changes shirts often and drinks a couple of gallons of water on the hottest days. He avoids alcohol, which can be dehydrating, during the workweek.