How to Build Up Your Heat Tolerance for a Hotter World

AAs the world continues to feel the effects of climate change, research suggests that the severity and frequency of extreme weather events – such as unrelenting heat waves – will only increase over time.

“We shouldn’t worry — we should be afraid,” says Camilo Mora, an associate professor in the Department of Geography and the Environment at the University of Hawai’i at Mānoa. “We are dealing here between something bad and something terrible,” depending on what action is taken to curb climate change.

For a study published in nature climate change In 2017, Mora and his colleagues analyzed hundreds of extreme heat events around the world and found that while about 30% of the population was exposed to a deadly combination of heat and humidity for at least 20 days a year, that percentage would rise to almost the halfway to the year 2100.

Heat and humidity can be harmful. In another 2017 study published in Circulatory system: cardiovascular quality and outcomes, Mora described 27 ways a heat wave can kill, such as insufficient blood flow to the brain, heart, kidneys, liver or pancreas. “It’s like a horror movie with 27 endings to choose from,” he says.

However, it is possible to prepare for a hotter world by building your heat tolerance, although experts say this isn’t necessary for everyone. Here’s what you should know about how people can and can’t adapt to rising temperatures.

What is heat tolerance?

The Occupational Safety and Health Administration (OSHA) defines heat tolerance as “the physiological ability to endure heat and regulate body temperature at average or better than others.”

Heat tolerance likely has a genetic component, although this link is not yet well understood. “Our nervous systems don’t all work exactly the same,” says Thomas E. Bernard, a professor in the College of Public Health at the University of South Florida, who studies heat-related occupational health and safety. “Just as you have high achievers in terms of intelligence, you have high achievers in a neurophysiological sense. There’s nothing you can do about that.”

Age is another contributing factor: Very young children and the elderly are at particularly high risk for heat illness, Bernard says. In addition, drug and alcohol use, the presence of acute or chronic disease, and obesity can negatively impact heat tolerance, while improving cardiovascular fitness increases it.

Continue reading: Why extreme heat is so bad for the human body

Hydration status also plays a role in how well someone performs in warm weather. Staying hydrated “doesn’t make you superhuman, but it does allow you to continue to endure the heat,” says Bernard. (However, once you’re well hydrated, “more doesn’t help.”)

Other factors that affect a person’s heat tolerance are more situational, such as: B. how long a heat wave lasted. Heat tolerance tends to decrease when it is extremely hot for many days. For example, if you work outside with high temperatures for the fourth straight day, you probably won’t do as well as you did on the first day.

While no one is immune to heat, most people have “an innate ability to tolerate some things,” says Michael F. Bergeron, who advises the Women’s Tennis Association on performance health and has done extensive research on heat. “People who are healthy, used to the hot conditions and not overexposure to the sun can take a lot.”

Can you improve your heat tolerance?

Humans can do many things to improve their ability to tolerate or adapt to changes in the environment. The best method is heat acclimation, which is “the process by which the body prepares all of these physiological systems to better handle heat stress,” says W. Larry Kenney, professor of physiology and kinesiology at Penn State. To acclimate, he says, you could go outside on a hot day and engage in light activity like walking for a very short time — about 15 minutes — and repeat the process the next day. The average person takes between nine and 14 exposures to acclimate, says Kenney. “The fitter you are, the shorter this time.”

Continue reading: How to cool off when it’s really hot outside

Several things happen during the acclimatization process that improve a person’s ability to tolerate heat. Above all, the blood volume expands. “This doesn’t allow the heart to work as hard and allows for more fluid to sweat,” says Kenney.

After the first few days of acclimation — which is all about cardiovascular adjustments — “the sweating mechanism starts to gear up, and we produce more sweat,” says Kenney. Also, the sweat we produce becomes more diluted, which means we lose less salt, and it occurs more often on the limbs. “When people aren’t acclimatized, they tend to sweat mostly on their core, face, back, and chest,” says Kenney. “But the best way to evaporate sweat is to spread it all over your body. So if you can sweat more on the limbs that move around the room quite a bit, that sweat can evaporate better.”

Heat acclimation is often a focus for athletes, people who work outside, and the military, says Brenda Jacklitsch, a health scientist at the US Centers for Disease Control and Prevention’s National Institute for Occupational Safety and Health. For example, some farm workers who spend their days spraying pesticides must wear protective equipment such as long sleeves, trousers and respirators, all of which increase the likelihood of heat-related illness – hence the need to acclimate.

Jacklitsch advises people trying to build their heat tolerance to slowly acclimate to hot environments over a week or two. Those new to working outdoors benefit from relaxing, spending maybe 20% of their first day in the heat, and then gradually increasing that time for the rest of the week.

Even when someone is fully acclimated, she notes, they are still susceptible to heat stress and could become ill. That’s why it’s important to always be with other people, take breaks in the shade, and drink well. Also, heat acclimation isn’t static: “Once you get a better tolerance, you need to maintain it because when you’re no longer in the heat, that resilience can drop,” says Bergeron.

While acclimatization is helpful for those who can’t escape the heat, experts agree it’s not necessary for the average person, and overexerting yourself could lead to heat illness. There’s nothing wrong with crouching in the air conditioner during heat waves. “You’re not doing yourself any favors,” says Bernard. “Their tolerance to heat may not be maximized – but it’s uncomfortable [to become acclimatized]. Why would you do that if you don’t have to?”

Will humans adapt to extreme heat?

For years, climate researchers have described a wet-bulb temperature of 35 degrees Fahrenheit as the upper limit for humans to be able to safely regulate their body temperature. (Wet-bulb) temperature is a measurement used by researchers that accounts for both heat and humidity. It is the temperature that would be measured by a thermometer covered with a cloth soaked in water; at 100% humidity, it is the same as air temperature. )

Thought about the maximum sustainable wet-bulb temperature has evolved, thanks in part to Kenney’s research. He and his colleagues send volunteers of all ages into climate chambers and adjust humidity and temperature while monitoring participants’ core temperatures. Participants swallow a pill that allows researchers to monitor their deep body temperature, and while in the chamber they move around, perhaps walking on a treadmill, as the temperature and humidity fluctuate.

Continue reading: A hotter world means more disease outbreaks in our future

Kenney’s results suggest that even for healthy people, the “critical upper limits” are closer to a wet-bulb temperature of 88 degrees Fahrenheit — which would mean, for example, 88 degrees at 100% humidity or 100 degrees at 60% humidity. At this point, Kenney says, “the sweat that’s produced isn’t evaporating,” so the body can’t cool down. But that doesn’t mean instant death. “People stopped the activity, went inside, sought shade and drank more fluids. No one would cross those limits for any length of time.”

These conditions are not yet widespread on Earth, although some areas have approached them during recent heat waves. If the world experiences another 2.5 to 3 degrees Celsius (or 4.5 to 5.4 degrees Fahrenheit) of warming, significant portions of the population could routinely exceed those thresholds, says Matthew Huber, a climate scientist at Purdue University.

Experts agree that humans cannot physiologically adapt to such extreme heat, not even for centuries to come. As Huber puts it, human internal body temperature is “a common property from 100 million years ago. It’s not something that changes quickly.”

However, this does not mean that the human species will cease to exist. Rather, we must rely on behavioral adjustments and other interventions. According to Huber, in some areas of the tropics and subtropics it is already common for workers to work at different times, i.e. to work from 4 a.m. to 11 a.m. and then to spend the hottest part of the day indoors. This could become normal in other places.

The world will also need improved access to air conditioning, as well as cheaper, more energy-efficient forms of cooling like electric fans. We may be seeing more “swamp coolers” — devices that use moisture to cool air, says Kenney. “I think what needs to happen is better engineering controls that bring this type of cooling equipment to more and more people who can’t afford it.”

Also, Huber emphasizes, we need to change our attitude towards the heat — and not push ourselves to run when it’s really hot outside or try to get through it because “Grandma used to live in this house without air conditioning.”

“There needs to be a shift in people’s mindset where they need to start seeing hot, humid conditions as actually a threat and not something that needs to be overcome,” he says.

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