Health

How to build your heat tolerance for a hotter world


Onethe world continues to feel the effects of climate change, research to show that that the severity and frequency of extreme weather events — such as incessant heat waves — will only get worse over time.

Camilo Mora, associate professor in the department of geography and the environment at the University of Hawai’i in Mānoa, says: “We shouldn’t be worried – we should be scared. “What we are dealing with here is between something bad and something terrible,” depending on what actions are taken to limit climate change.

For a study published in Natural climate change In 2017, Mora and his colleagues analyzed hundreds of extreme heat events around the world and determined that, while about 30% of the population is exposed to a deadly combination of heat and heat, humidity for at least 20 days annually, that percentage will increase to nearly half by 2100.

Heat and humidity can be very dangerous. In another 2017 study, published in Circulatory: Cardiovascular quality and outcomesMora described 27 ways a heat wave can kill, such as insufficient blood flow to the brain, heart, kidneys, liver or pancreas. “It was like a horror movie with 27 endings to choose from,” he said.

However, you can prepare for a hotter world by building up your heat tolerance, although experts say doing so isn’t necessary for everyone. Here’s what to know about how humans can adapt to rising temperatures and the ways they can’t.

What is heat resistance?

Occupational Safety and Health Administration (OSHA) determined Heat tolerance is “the physiological ability to withstand heat and regulate body temperature at an average or better rate than others”.

Heat tolerance may have a genetic component, although that link is still poorly understood. “Our nervous system is down,” says Thomas E. Bernard, a professor at the College of Public Health at the University of South Florida who studies occupational health and safety in the heat. exactly alike. “Just like you have a high score in terms of intelligence, you have a high score on neurophysiology. There is nothing you can do to change that.”

Age is another contributing factor: young children and the elderly are at particularly high risk of heat illness, says Bernard. In addition, drug and alcohol use, the presence of acute or chronic illness, and obesity can negatively affect heat tolerance, whereas improving heart health will increase it.

Read more: Why is too high a temperature harmful to the human body?

Hydration status also plays a role in how well a person feels in warm weather. Drink enough water “It doesn’t make you superhuman, but it allows you to continue to tolerate the heat,” says Bernard. (Once you’re well hydrated, however, “more won’t help.”)

Other factors that affect a person’s tolerance to heat are more situational, such as how long a heatwave lasts. Heat resistance tends to decrease when it is extremely hot for days. For example, if you’re working outside on the fourth day in a row with high heat, you probably won’t do as well as the first day.

Michael F. Bergeron, who advises the Women’s Tennis Association on performance health and has intensively research heat. “People who are healthy and used to hot conditions, and don’t expose themselves excessively to work or exercise in the sun, can tolerate a lot.”

Can you improve your heat tolerance?

People can do much to increase their ability to withstand or adapt to changes in the environment. W. Larry Kenney, professor of physiology and kinetics at Penn State, says the best method is acclimation to heat, which is “the process by which the body adjusts all of these physiological systems to handle stress. better thermal straightness”. To get used to your body, he says, you can go outside on a hot day and do light activities — like going for a walk — for a very short period of time — about 15 minutes — and then repeat the process. this the next day. It takes the average person 9 to 14 exposures to become acclimated, says Kenney. “You are the right person, the shorter that time.”

Read more: How to cool down when it’s really hot

Several things happen during adaptation that improve a person’s tolerance to heat. Most notable is the expanded blood volume. “That allows the heart to not have to work so hard and it provides more fluid for sweating,” says Kenney.

After the first few days of getting used to the body — all aimed at regulating the cardiovascular system — “the sweat mechanism kicks in and we sweat more,” says Kenney. Plus, the sweat we produce is thinner, which means we lose less salt and that happens more often on the extremities. “When people aren’t used to getting used to, most of their sweat is on their torso, face, back, and chest,” says Kenney. “But the best way to evaporate sweat is to go all over the body. So it’s possible to sweat more on the extremities, which are moving through space quite a bit, allowing that sweat to evaporate better.”

Brenda Jacklitsch, a health scientist with the US Centers for Disease Control and Prevention’s National Institute for Occupational Safety and Health, says temperature adaptation is often a focus for athletes. , people working outside and the military. For example, some farm workers who spend their days spraying pesticides have to wear protective equipment such as long sleeves, long pants and respirators, all of which increase the likelihood of heat-related illness – therefore need to adapt.

Jacklitsch advises people trying to build up their heat tolerance to slowly acclimate to hot environments over one to two weeks. Those new to working outside benefit from relaxation, perhaps spending 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 stress and can get sick. That’s why it’s important to always be around others, rest in the shade, and stay hydrated. Also, adaptation to heat is not static: “Once you have better tolerance, you have to maintain it, because if you are not in the heat anymore, that resilience can be impaired.” decrease,” Bergeron said.

While acclimatization is helpful for those who can’t escape the heat, experts agree it’s not necessary for the average person and that pushing yourself can lead to heat illness. . There’s nothing wrong with bending over the air conditioner during heat waves. “You don’t consider yourself a disruptor,” says Bernard. “Your heat tolerance may not be at its maximum – but it’s annoying [to become acclimatized]. Why would you want to do that unless you have to? “

Will humans adapt to extreme temperatures?

For many years, climatologists have described the wet bulb temperature as 95 degrees Fahrenheit is the upper limit for humans to safely regulate body temperature. (The “wet bulb” temperature is a measurement used by the researchers to measure both heat and humidity. That’s what would be read by a thermometer wrapped in a cloth soaked in water; at 100 humidity. %, it is equal to the air temperature.)

Thoughts on sustainable maximum wet bulb temperatures have evolved, thanks in part to Kenney’s research. He and his colleagues sent volunteers of all ages into environmental chambers and adjusted the humidity and temperature, while monitoring the participants’ core temperatures. The participants swallowed a pill that allowed the researchers to monitor their deep body temperature and, once inside the chamber, they moved around, possibly walking on a treadmill as the temperature and humidity levels increased. oscillate.

Read more: A hotter world means more disease outbreaks in our future

Kenney’s findings indicate that the “critical upper limit,” even for healthy individuals, is close to a wet bulb temperature of 88 degrees Fahrenheit — which means, for example, 88 degrees at 100% humidity. or 100 degrees at 60% humidity. At that point, “the sweat you put out doesn’t evaporate,” says Kenney, so the body can no longer cool itself. But that does not mean instant death. “People will stop being active, go inside, find shade and drink more fluids. No one can continue to exceed those limits for long. “

These conditions are not yet common on Earth, although some areas come close them during recent heat waves. Matthew Huber, a climate scientist at Purdue University, said that if the world experiences an additional 2.5 to 3 degrees Celsius of warming (or 4.5 to 5.4 degrees Fahrenheit), a significant portion of the population may start to break these thresholds frequently.

Experts agree that, physiologically, humans will not be able to adapt to such extreme temperatures – even within the next few centuries. As Huber put it, the internal body temperature of humans is “a common feature, from 100 million years ago. It’s not something that changes quickly.”

However, that does not mean that humanity will cease to exist. Instead, we will need to depend on behavioral modifications and other interventions. In some tropical and subtropical areas, says Huber, workers often work shift hours, such as working from 4 a.m. to 11 a.m., then spend the hottest part of the day outside, says Huber. in. That may become the norm elsewhere.

The world will also need to improve accessibility air conditioner, as well as cheaper, more energy-efficient forms of cooling, like electric fans. We might see “swamp coolers” more often, says Kenney—devices that use moisture to cool the air. “I think what’s going to have to happen is better engineering controls to make those types of coolers available to more and more people who can’t afford them.”

Plus, Huber stresses, we’ll need to change our mindset about the heat – and not force ourselves to run when it’s very hot outside, or push through because “she used to live in this house.” there’s no air conditioning.”

“There’s going to have to be a shift in people’s thinking, where they have to start thinking about hot and humid conditions as a real threat and not something that needs to be fixed,” he said.

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