Higher Temperatures Are Bad For The Body

SOPHIE BUSHWICK: This is Science Friday. I’m Sophie Bushwick. Across the globe, hundreds of millions of people have been dealing with extreme heat. The three most populated countries in the world, China, India, and the US, have been gripped by heat waves over the past few weeks.

Extreme heat isn’t just uncomfortable. It can be deadly, especially for our most vulnerable populations. In the United States, heat is responsible for more deaths than any other type of weather event. Joining me to talk about what high temps do to the body and how we can protect our health and safety is my guest Chris Uejio, associate professor of public health at Florida State University in Tallahassee, Florida. Welcome to Science Friday.

CHRIS UEJIO: Thank you for having me.

SOPHIE BUSHWICK: Walk me through what happens in the body when we’re exposed to extreme heat. I know from personal experience that I get covered in sweat, and my face turns red. But what’s going on inside? How do human organs and systems react to heat?

CHRIS UEJIO: Sure. Wonderful question. So humans are warm-blooded creatures, so we have to maintain a consistent core body temperature to function properly. So essentially, this is an energy balance problem when we’re exposed to extreme heat for a long period of time. We essentially don’t want our body’s heat storage to gain heat that’s going to increase our core body temperature to dangerous levels.

So our body is pretty good at coping with heat and environmental threats. So the skin and the central nervous systems have thermoreceptors that can sense when it needs to respond by two primary mechanisms. Release sweating, just as you mentioned, which is our most effective and energy-efficient method. And the second one, which we don’t think about as much, is increasing blood flow and trying to dissipate heat from the core of our body to our skin.

So sweating leads to evaporative cooling, which can be kind of miserable, but it is really our most effective way to cool our bodies down. But when there are hotter and/or humid conditions, we can start to see that that is restricting the rate of our sweat being able to evaporate over the core body, and that can lead to dehydration. Increasing blood flow and heat to the skin is kind of a complex mechanism. But it essentially increases our heart rate, our heart’s ability to contract, the amount of blood being pumped to our skin. And essentially, since our body and our cardiovascular system have to work harder, that can lead to an increased risk of adverse cardiovascular events, such as heart attacks or strokes.

SOPHIE BUSHWICK: And how do those effects change when the heat wave lasts for many days or even weeks?

CHRIS UEJIO: Great question. We know that heat waves, periods of abnormally hot and/or humid conditions for more than two days, consecutive days, can strain the human body further. There’s unfortunately not a lot of evidence from laboratory studies. There’s some preliminary evidence that suggests that there is a cumulative effect of heat gain in the body over a multiple-day period.

So essentially, being stressed over multiple days doesn’t give the body the ability to dissipate that heat to cool down to restore some of those normal bodily functions and to rehydrate. So these longer and prolonged periods of heat can stress our bodies over both the short term and over the long period, which is really an exciting area of research that’s going on right now.

SOPHIE BUSHWICK: And what about heat stroke? When does the body’s reaction to heat sort of cross that line and become heat stroke?

CHRIS UEJIO: Yeah. So while the symptoms between heat exhaustion and heat stroke are fairly similar, our sort of gold standard is when your core body temperature is rising above 103 degrees Fahrenheit on its way to 104 degrees Fahrenheit. And that’s going to be accompanied by some of the same symptoms as heat exhaustion, such as some mental health and confusion, dizziness, nausea. It can be accompanied by either excess sweating or, if one is getting dehydrated, losing the ability to sweat, and potentially blacking out or losing consciousness.

SOPHIE BUSHWICK: And how fatal is heat stroke?

CHRIS UEJIO: Sure. So heat stroke, if not treated in a rapid fashion, can be quite fatal. It is essentially overwhelming multiple organelles– the cardiovascular, respiratory, renal systems. But that being said, sports medicine and a variety of other medical professions have some pretty tried and true techniques to cool the body down rapidly.

For example, the Korey Stringer Institute in the United States has pioneered some techniques to cool the body down. Essentially, put someone in an ice bath, or barring having an ice bath, filling a bag and putting someone in a bag full of ice until their core body temperature is lowered to a safe level before transporting them to a health care facility for further care.

SOPHIE BUSHWICK: So it sounds like that’s essentially just a very, very cold bath.

CHRIS UEJIO: It is. It’s the type of thing that would be great for a polar bear, but can be life saving.

SOPHIE BUSHWICK: And who is most at risk for adverse health effects in the heat?

CHRIS UEJIO: So everyone faces some risks from extreme heat, particularly during the hot prolonged and humid periods that you had mentioned. But we are most concerned about some groups. That includes older adults and people with pre-existing health conditions, since heat affects many of those body systems that we discussed. Older adults also store heat for a longer period of time and are less capable of dissipating it. They also have a lower ability to detect when they’re thirsty.

There are some other key risk groups as well for heat. Those include low-income households, who essentially have difficulty paying for electricity. Some of the poorest households spend about 16% of their income on electricity, which is comparable to the amount spent on food or transportation. We’re also worried about people who are outdoors, whether that’s outdoor workers or people who exercise outdoors during these hot or humid periods, people who are unhoused and do not have the ability to access safer, cooler spaces, and finally, pregnant people and younger children.

SOPHIE BUSHWICK: And you mentioned a couple things the body does to try to cool itself down– sweating and having blood flow to the skin. But can you go into a little more detail about how that works? How does an uncomfortable layer of sweat help my body stay cool?

CHRIS UEJIO: Yeah, great question. So when you’re essentially drenched with sweat, perhaps one way to think about it would be to compare if you’ve ever visited more of a dry, desert heat versus a hotter, humid more heat. Let’s just say it’s the same temperature, roughly, say something like 100 degrees Fahrenheit. In a dry desert heat, you would start to become sticky because the sweat is evaporating almost instantaneously off your body. And then you are cooling down fairly effectively, but your next concern, then, would be replacing those fluids and avoiding dehydration and some of the challenges that that may bring.

In contrast, when you’re in a hot and humid climate, and your body is sweating, and you’re drenched with sweat, it will continue to sweat, essentially because it’s not cooling down fast enough. It’s saying, I know this is my best card to play, I’m going to keep playing it. And that’s when your body starts to be drenched with sweat. And depending on the conditions and the difference between the moisture on your skin and in the air– essentially, how humid it is– that will sort of dictate if your body can reach some sort of balance or if you need to go to an air-conditioned space to reach that balance.

SOPHIE BUSHWICK: What happens if your body– if you’re in a humid environment, so your sweat’s not really evaporating as much as it needs to to cool you off, but you don’t have an AC. What happens to your body if it’s unsuccessful in this cooling effort?

CHRIS UEJIO: Great questions. So essentially, the body will continue to gain heat, and that’s going to increase our core body temperature. The body is still going to try to push on these two levers of increasing its sweat rate and increasing blood flow to the skin. But then, essentially, a lot of our key body systems start to not function as well or face some challenges. And those include our cardiovascular system, our respiratory system, and our kidneys. So essentially, our body starts to shut down.

SOPHIE BUSHWICK: I want to talk about other parts of the world outside the United States. There seems to be a misconception out there that traditionally warmer countries like India or Pakistan are better equipped to handle heat waves. But both of those countries have been really struggling with this heat. What’s going on here?

CHRIS UEJIO: So there appears to be a misconception that people in hotter and more humid climates, such as the tropics, are innately more suited to cope with extreme heat. But there’s no evidence based on the human body’s physiology that people in these hotter, more humid climates, tropical climates, are innately more able to cope with heat. So stated another way, it’s much more likely that there is a substantial burden of extreme heat on these communities already and that it’s just not being measured.

SOPHIE BUSHWICK: And only 8% of India’s population has air conditioning. How does AC access affect how countries are equipped to deal with heat waves?

CHRIS UEJIO: Great question. In this area of climate change where climate change is raising average temperatures, it’s making our extreme heat events more frequent, intense, longer lasting, and geographically widespread, air conditioning has transitioned, unfortunately, from being more of a luxury to being absolutely critical for some of these key subgroups in places with hot and/or hot and humid climates. So for better or for worse, air conditioning is our most effective intervention to prevent heat-related illness and death.

SOPHIE BUSHWICK: So you mentioned climate change increasing the need for air conditioners. What are your other big concerns as climate change makes heat waves more and more common?

CHRIS UEJIO: Sure. Extreme heat challenges public health. And that’s what I’m most concerned about. But extreme heat has some really profound implications for our functioning of our economies. We know that at relatively regular or everyday conditions in much of the world, that extreme heat is sufficiently hot to impair productivity, to lead to more accidents and injuries, impair cognitive functioning, limit the ability of our children to learn in schools. This is sort of an all-encompassing challenge that we need to step up to the plate to.

SOPHIE BUSHWICK: You’ve worked with some cities to address this, to make heat resiliency plans. What are some strategies for keeping cities cool?

CHRIS UEJIO: Cities are in the early stages of pioneering some neat strategies to equitably and justly address extreme heat. So for example, New York City, during COVID-19 and its subsequent waves, decided that it wasn’t safe to open their cooling centers or refuges. And these, for context, are historically probably the most common method that cities have used to adapt to extreme heat, would be to open a city-owned space like a library to people to cool down for a few hours. New York City switched to handing out portable air-conditioning units to about 70,000 people, including giving vouchers so that they not only have an air-conditioning unit, but they have the ability to pay for it.

There’s a variety of non-air-conditioning-based techniques and priorities people are looking at. Probably the most popular one is tree-planting initiatives and green infrastructure or cooling infrastructure. And pretty uniformly across the US, people are interested in these, whether it’s a place like Orlando, Florida, that is trying to increase its tree canopy cover up to 40% by the middle of the century, places like Miami-Dade County, which has the world’s first chief heat resilience officer in Jane Gilbert. So there are many innovative strategies, but they’re just starting to get off the ground.

SOPHIE BUSHWICK: This is Science Friday from WNYC Studios. We’re talking to Chris Uejio, who studies climate change and human health at Florida State University in Tallahassee, about how people and cities can deal with extreme heat. And do these strategies apply to all cities, or are there exceptions? For example, do these strategies work just as well in New York as in Los Angeles?

CHRIS UEJIO: Yes, excellent point. So the strategies in general can be somewhat transferable if they’re tailored to a specific location. So running with the issue of tree planting, a place like Phoenix, Arizona, where Dave Hondula and a variety of others are working on adapting to extreme heat, they’re also going to be considering some of the more complex trade-offs with tree planting.

So in an area like Phoenix, which is also seeing challenges due to water availability, they’ll also perhaps prioritize trees that don’t require a lot of extra water, which primarily is going to be native vegetation. But that does provide a lot of shading. In a place like Miami, someone may have to think about which trees are also resilient to storm surge or some saltwater exposure, too, when you’re planning some of these efforts.

SOPHIE BUSHWICK: And what if someone’s in a situation where the cities are super hot, but they don’t have trees or even AC. Are there other methods that they can use to keep themselves cool?

CHRIS UEJIO: Great question. Unfortunately, the sort of last-resort strategy that we have at the moment– and even this is still under development– we know the pace of climate change is outpacing our ability to build solid evidence to adapt to it. So one of these strategies would be partially immersing part of your body, whether that’s putting your leg or an arm into, say, a room-temperature body of water. It doesn’t have to be particularly cold, but just turning on the cold water or room temperature for a certain number of minutes, say 20 minutes, to provide some heat relief.

That being said, one of the challenges is that a lot of people who suffer from extreme heat do not necessarily know or are as cognizant that they’re experiencing those symptoms. Maybe they just feel a little off that day. So it will still be one of the challenges for them to recognize that it could be extreme heat and to take some action.

SOPHIE BUSHWICK: And in that case, how do you even know that you have heat stroke?

CHRIS UEJIO: Great point. Somewhat like COVID, we have to look at multiple converging lines of symptoms. So for example, if one has dizziness, thirst, heavy sweating, or recently were heavy sweating and it stopped, nausea, or weakness, it’s best to err on the side of caution and then start to call for help, whether that’s from a neighbor who’s checking in on you or calling 911, particularly as you move to more confusion or more of the severe symptoms of heat stroke. If one has the ability to take their temperature, that also could help. But looking collectively at the symptoms and erring on the side of caution can make a lot of sense.

SOPHIE BUSHWICK: That’s all the time we have for now. I’d like to thank my guest, Chris Uejio, associate professor of public health at Florida State University in Tallahassee, Florida. Thanks for joining us, Chris.

CHRIS UEJIO: Thanks, Sophie.

SOPHIE BUSHWICK: Speaking of how our warming climate changes the world around us, we’ve got a book recommendation. This one comes from Science Friday Book Club member Tom in Duluth, Minnesota.

TOM: The book I’m looking forward to reading this summer is by Erica Gies, and it’s called Water Always Wins– Going With the Flow to Thrive in the Age of Droughts, Floods, and Climate Change. These days, in the face of climate change, as we build more and more areas and lay down more pavement, we need to think about how we can slow the flow of water through our landscapes and reduce impacts on our infrastructure. I’m hoping this book will be a very interesting read. Thanks.

SOPHIE BUSHWICK: If you’d like to join Tom in our SciFri Book Club, head to sciencefriday.com/bookclub. Our book clubbers are currently reading Upgrade by Blake Crouch. You can join the conversation and see what we’re reading next. That’s all at sciencefriday.com/bookclub.

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