Spotlight on Health & Climate Change: Extreme heat and health

Dr Patricia Fabian and Professor Ollie Jay join Lancet editors Saleha Hassan and Pierre Nauleau to discuss the current and potential future impacts of climate-change induced extreme heat on health - from the mechanisms that link temperature and health to potential adaptation strategies to build resilience in a heating world.

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Transcript

This transcript was automatically generated using speech recognition technology and may differ from the original audio. In citing or otherwise referring to the contents of this podcast, please ensure that you are quoting the recorded audio rather than this transcript.

Saleha: Hello and welcome to the Lancet Voice Podcast. I am Saleha Hassan, Senior Editor of the Lancet Infectious Diseases. And I'm joined by my colleague, Pierre Nowlow, who is a US based editor for eBiomedicine. This marks the 200th year of the Lancet, and we have been shining a light on multiple areas of health throughout the year.

This podcast is focused on extreme heat and health, and is part of a larger spotlight called Health and Climate Change. In the past 20 years, there has been a 54 percent increase in heat related mortality among people aged 65 years and over. The most recent Lancet Climate Change and Health Countdown reported that extreme heat was associated with a plethora of human diseases, ranging from cardiovascular and respiratory diseases to suicide, injuries, and diabetes.

Today, we will be discussing the mechanisms by which heat affects the human body. So what is known and what is unknown, and also the adaptation strategies, both microcosmic and macrocosmic, that can reduce the burden of extreme heat on health and build resilience in a heating world. I will pass on to Pierre now to introduce our speakers for today.

Pierre: Thank you, Celia. So today we are really pleased to have Olijay, who is Professor of Fetal Health at the University of Sydney, and we also have Patricia Fabian, who is an Associate Professor on Environmental Health at the Boston University School of Public Health, and Associate Director at the Boston University Institute of Global Sustainability.

Thank you for being with us today. Would you like to start, maybe to introduce you a little less formally, to tell us what you're currently working on? 

Patricia: Sure. Thank you for the invitation. Thank you for the introduction. As I said, my name is Patricia Fabian. I'm an associate professor at Boston University and a lot of my work straddles climate and health and sustainability.

My expertise is around indoor air, built environment, and trade offs. It's decisions that we make around things like weatherization and heat and health. Specifically related to heat, I co lead a project with a colleague, Dr. Madeline Skamal, that's a community engaged project in environmental justice communities, and it's about building resilience to extreme heat in vulnerable communities, which I know we'll be talking about a lot today.

That really involves working with the city, working with the communities, working with the residents. And my role, also, in the CC run, which is a Know the kind of network of climate researchers. It's also bringing health into a lot of the climate conversations. And then my other project related to heat is looking at heat in schools.

Schools fall through the cracks in terms of funding and research and impacts of climate and environmental health. And so working with Boston Public Schools to understand exposures to temperature and evaluate things like interventions around classrooms. 

Ollie: Thank you, Pierre, and thank you for the introduction and the opportunity to speak with you today.

Yeah, my name is Ollie Jay. I'm a professor of heat and health at the University of Sydney in Australia. And I'm director of a new research center. It's called the Heat and Health Research Incubator. And what we're seeking to do with the incubator is establish a multidisciplinary platform to enable researchers, stakeholders, people from a variety of different backgrounds to come together to generate a truly multidisciplinary approach to solving these very complex problems that we face in the world.

In the context of climate change with respect to extreme heat and hot weather on human health being across the human lifespan. So the specific work that I focus on myself and within my own research group, I'm a physiologist. So I really focus on the way in which the human interacts with the thermal environment.

And really trying to get a better understanding of the way in which It's not just temperature that impacts human health. It's a variety of different environmental characteristics that define a thermal environment. I try to understand how we can utilize that, that balance between the environment and the human body to develop evidence based, low resource, Cooling strategies to help the most vulnerable navigate their way through extreme heat events.

Pierre: Thank you. Thank you for this brief summary. Yeah, we have lots of questions for you because it sounds super interesting. So maybe to start with Patricia, maybe you can explain what is considered extreme heat by the research and the clinical communities. 

Patricia: So maybe I'll start. So one term that everybody is familiar with, I think around the world is That makes the news mostly because it's Usually results in a number of deaths, and some examples are, for example, in the United States, more recently, the heat dome of the Pacific Northwest, so it happened in Northwest United States in June 2021.

Temperatures reached 47 degrees centigrade and over 120 people died, many of hyperthermia. That is one recent example that got a lot of press and news. But obviously there's a lot more examples in history and a really big one would be the 2003 heat wave of Europe, which killed more than 50, 000 people.

However, I think what's challenging is that there's lots of definitions of heat waves. In general, it means a period of abnormally and uncomfortably hot and humid weather. So that, I think, is a pretty general definition that we can all agree on. It's hotter than usual. But then if you want to do research or look at what the association is of a heat wave on health, you have to be way more precise than that.

There's another definition from the Intergovernmental Panel on Climate Change that says a heat wave is in reference to a specific temperature threshold. It varies depending on where you are in the world, and it can last anything from two days, two months. Some more precision, but still not quite enough for us to know what is a heat wave.

World Meteorological Organization defines it as the daily maximum temperature of more than five consecutive days exceeding five degrees centigrade, the normal period, and it takes a reference of 40 years to compare that. And in research, what we do is we pick other types of ways to define heat wave, and one example is two or more consecutive days where the daily 99th percentile of the collected data.

So pretty complicated, actually, what seems a really Simple concept of saying it's hotter than usual, those definitions actually take into account humidity. The way that bodies cool off is that you perspire, right? You evapotranspire. So when it gets hot, you start sweating, that cools your body off. And when the humidity is high around you, then your body can't evaporate.

And so it can't cool off quite enough. And so when it's really humid, It actually feels hotter. Just an example, if it's 90 degrees Fahrenheit, I should have converted that to centigrade, and 40 percent humidity, it feels like it's 90 degrees. But if it's 90 percent humidity, then it feels like it's 120 degrees.

And so the capacity for bodies to cool down goes down. 

Saleha: Thank you so much, Patricia. Olly, what are the main effects of extreme heat on the human body? And how are these mechanisms investigated? 

Ollie: I think this is a really important question to get a grips with on this particular topic. As Patricia alluded to in her previous response is, Hyperthermia is the condition that most people associate with extreme heat exposure.

And by definition, from a physiological perspective, hyper, or from a clinical perspective, hyperthermia is a critical rise in internal body temperature, beyond what is normal to the point where it becomes dangerous. High body temperatures or high core temperatures are actually not necessarily the responsible for the majority of heat related hospitalizations.

And we can really break it down to three predominant parts and through underlying cause for them are ultimately heat exposure, but the pathophysiological pathways are different. So the first one's the standard one, which is heat stroke, which that's the the end point of a continuum of Heat illnesses which start off with mild heat exhaustion to severe heat extortion all the way up to heat stroke.

What happens with heat stroke is that it's allied to the fact that the way in which we try to physiologically defend body temperature, we do two things. We sweat, and it's the evaporation of that sweat that cools us down, not the production of sweat. But we also have this early response, which is called a cutaneous vasodilation.

So this is basically where we're redirecting or redistributing a lot of our blood from deep inside the body core towards the skin surface to support skin surface. Thanks. heat transfer. Now, what we know is that through animal studies that, that various physiologists have done, is that this effectively deprives the gut of heat.

of oxygen delivery via the bloodstream because of this redistribution of blood. And when you have this low level of oxygen delivery to the gut accompanied by high tissue temperatures, this causes the guts to start to have an increase in permeability. And then endotoxins that normally reside within the gut and start leaking out, they enter the circulation, and then they set off a cascade of effects, which results in mass coagulation, multiple organ failure, and death.

And that's why heat stroke is a medical emergency and treatment of people demonstrating with the signs and symptoms of heat stroke. It's really important that they're treated rapidly and aggressively. But that's, from an epidemiological perspective, that's predominant in most cases, that's the minority of cases that turn up in hospital or in the mortality statistics.

People with cardiovascular disease are often at a much greater risk during extreme heat events. And this now comes down to the way in which the body tries to defend. Body temperature. So the thermoregulation response of this vasodilation, again, it's the redistribution of blood towards the skin. What the body has to do is not only are we trying to support body cooling, but we also have to defend blood pressure.

And in order, when you're redistributing all that blood towards the skin and you want to maintain central blood pressure, you've got to increase something called cardiac output. And cardiac output is a product of heart rate and stroke volume. So the amount of blood that is shifted with every contraction of the heart.

That goes, if anything, goes down when we're very hot because we have low venous filling pressure. So this requires the heart to do a lot more work. It needs to beat a lot, many more times per minute. And the oxygen delivery and oxygen requirements to support that, those contractions goes up. Now, if you have an underlying cardiovascular infirmity, such as coronary artery disease, it's quite obvious that is a bit of a recipe for disaster.

And then finally, we've got the pathway of dehydration. The other way in which we defend body temperatures by sweating and If we don't replenish those lost fluids, particularly over the course of a prolonged heat wave, Patricia was mentioning definitions of heat waves, as short as two days, but as long as, several days, even weeks.

Those sustained heat exposures in settings where maybe we don't have access to a lot of cooling, it means that we have to drink a lot of water. If we don't replenish those lost body fluids, then we have a decrease in heat. in our blood volume, and that will then place extra strain on the kidneys, but it also compromises the risk of, or increases the risk of, heat stroke and also cardiovascular collapse as well.

Just as a bit of an idea, so when we're sitting passively, so resting in the heat, it wouldn't be unusual for us to sweat around about half a litre of sweat per hour. So you can imagine if that happens over the course of several days. Without adequately replenishing those body fluids, eventually we get to a body water deficit that becomes quite dangerous.

Pierre: Excellent. And you already started to trailer to it, but maybe we can discuss a little bit more in detail which population was vulnerable to extreme heat and maybe why. 

Patricia: I think I will leave the vulnerability due to sociology causes to Ali to talk about, because we know, for example, age, comorbidities, taking medications.

Those are physiological reasons why someone might be more vulnerable to heat. My work deals with thinking more about social determinants of health and other reasons why people might be vulnerable to heat. And those are a huge range. Some of them are socio demographics, so characteristics about how people live.

I'll talk a little bit more about that. Some of it is around urban cities, so the fact that people maybe live in cities and so the place where they are is hotter. And others are more social, so related to things like social isolation or language. So we have done studies looking, again, working with environmental justice communities, looking around Massachusetts, across the nation, building heat vulnerability indices.

And this is something that other researchers have also done all over the world. And it's thinking about why would someone be vulnerable to heat? If you think about, let's talk about the urbanicity piece. So people live in urban heat islands. An urban heat island is an area that's hotter than the surrounding rural areas.

It can be a city or a community. And there's heat islets within cities. So if you live in an area that's hotter, maybe 10 degrees hotter than someone who lives in an area with green space, you're more vulnerable to heat because your exposure is higher. You could live in multifamily housing and be a renter where you don't actually have the capacity to change things about your home.

So that makes you vulnerable because you have a little power to make changes. Income, obviously, is always something that makes populations vulnerable to disease all over the world for all sorts of reasons. In the case of heat, it could do, be related to housing quality, or ability to buy an air conditioner, or ability to pay for electric bills, for example.

Social isolation is important. We did a study, for example, looking at older adults and affordable housing, finding that, obviously, older adults are more vulnerable to heat for physiological reasons. The adults could pay for cooling, they could pay for electricity, they could pay for air, they had air conditioners, but they couldn't lift the air conditioners into the windows because they lived in an old building that didn't have central air.

So that sort of speaks to network connections, to sort of social connections. And that was the solution, actually, was to do a buddy program to, to help. And then on the sociodemographic side as well, things like English language learners. I'm in the United States, so I say English, but really it's whatever the native language might be.

The ability to know that there's heat warning, that there's a heat wave coming. What are the resources, things like cooling centers. So people are vulnerable who maybe don't have native language as a first language, people who might be unemployed. Where do you go? Our study when we started, it was during covid cooling centers were pretty much non-existent.

So people were going to go to a library or to a grocery store, no access to cooling centers. So that's just this really wide suite of examples of why people might be vulnerable to heat. 

Pierre: Or do you want to develop a little bit on the physiological side? 

Ollie: Yeah, absolutely. And I think one thing that's really important to understand is that it's when this physiological vulnerability that I'm about to describe coincides with the low behavioral adaptive capacity because of the circumstances that people find themselves in.

Having these physiological vulnerabilities in and of themselves are not necessarily critical if they're not exposed to the stressor. So if the limit. In a setting where there's air conditioning, where it's well insulated, where they're not exposed to the heat, you can have this physiological vulnerability, but it won't matter as much.

So it's this coincidence. between the physiological vulnerability and the low behavioral adaptive capacity. But just to summarize what the physiological features, so one of the things that we know is that we, so we, in the heat and health research incubator at the University of Sydney, we look at vulnerability across the human lifespan.

The way in which heat is a risk is different depending on where you are in the lifespan. Some excellent work that's demonstrated the negative health impacts associated with excess heat exposure during pregnancy, for example, The underlying causes are a bit of a mystery. We, ourselves, and just some other research groups around the world have received some funding to try to help get to the bottom of that.

When we're in the early stages of life, children have see infants have a very high surface area to mass ratio, which means the amount of surface area they have for gaining heat from the environment is great, is greater relative to their body mass, which is what determines temperature. Therefore they can heat up really quickly.

And then as we then get to adulthood, we can be. Exposed because of the type of occupational environment that we work in, if we work in agriculture, if we work in, in, in the manufacturing industry or something like that, that might result in, in, in excess heat exposure, despite a, not necessarily a physiological vulnerability, then we get to old age.

And this is where we start seeing age related reductions in the ability to sweat when we go back to that. Key point that sweating in the evaporation of sweat is the key mechanism for physiologically cooling ourself, we're exposed to it. If we have age related decrements in the ability to sweat, they're observed above 60 years old, they're particularly pronounced above 75 years old.

That is one of the reasons, probably, why we see older adults being at a much greater risk during extreme heat events. Now, if that primary aging. Is then accompanied by the presence of other chronic diseases, such as cardiovascular disease. renal disease, type two diabetes, things like this then that aggravates the heat stress risk.

Now, if we go back to my pre the answer to the previous question about the pathways of vulnerability, you can understand why those particular disorders might then aggravate heat health risk. Won't necessarily mean that you'll be at a greater risk of heat stroke, even though primary aging will. probably do that, but it will also, at the same time, present you as being at a greater risk of these cardiovascular effects or kidney effects and things like that.

One thing I just want to also comment on, which I think is really important, is the kind of the information that's available around medication. So it's quite often quoted in the public health literature That prescription medications, particularly anticholinergic medications and things like this, have a distinct impact on our ability to keep cool.

Now, again, if we go back to the epidemiological literature, there's some pretty good evidence that certain types of medication might increase risk or do increase risk, but the physiological evidence that Certain types of medication actually impair the ability to physiologically keep cool. It's actually really weak and that's an area that really needs a lot of investigation because at the same time particularly given that a lot of the medications That are often quoted are often used for the management of mental health challenges is that, and we know that extreme heat impacts people with mental health disorders in a greater way, if we then potentially suggesting that more advising that medications should be modified, or the regime should be modified during extreme heat that could potentially be a problem.

maybe a big problem. So I think generating more evidence, supporting the impact of different types of medication on the ability to physiologically keep cool is an absolute urgent matter that needs to be addressed. 

Saleha: Usually when we think about the effects of extreme heat on health, we think about direct effects, which you have alluded to so far.

But Ali, I'd also like to know if there are any other indirect ways that excessive heat can affect health and society at a population level? 

Ollie: Yeah, absolutely. And this is why the negative health effects of extreme heat and hot weather On human health being a so complex and this question now gives a bit of insight that I think so if I'll just give three examples, and there are many more examples, of course, but if we think about people in the workplace, some great work that was done in Australia back in 2015.

Try to quantify the economic impact of heat on the Australian economy. And they estimated that annually it costs the Australian economy 6 billion a year. And that was back in 2015. And since then, I think we've had five of the six hottest summers on rec since records began in 1893. So if anything, that number likely have gone up.

If we then look at workplaces in lower middle income countries, For example, the challenges that we see there are really tied to the nature in which people are employed. So we do some work with ready made garment factories in Bangladesh, for example. And what we know in those types of settings is that employees are paid based on their output, not on the amount of time they spend at work.

Now, the number one way in which we autonomically Behaviorally protect ourselves against the heat is through reduced physical activity. So if we're in the workplace, one of the things that would see if the activity is, it requires some elevated level of the physical activity. Sorry, the job requires an elevated levels of physical activity.

We all slow down. I will be more prone to make errors. And so the output in those settings will be poorer in these types of settings. It wouldn't be unusual for. People have to stay at work for an hour, an extra hour and a half per day in order to get paid the same amount because it's particularly hot.

And so this kind of gives us an idea of the impacts of extreme heat on people are very diverse, and it also depends on a variety of other factors. Other couple of examples I'll give, which is associated with some of the work that we're doing here in the Heat and Health Research Incubator at the University of Sydney right now, is looking at heat as a secondary aggravator.

Of the risk of mosquito borne diseases and waterborne diseases. So just to drill that into that a little deeper In areas of the world that have high prevalence of malaria, for example, the number one way in which we try to defend against it is overnight mosquito net use. And the number one barrier to mosquito net use compliance overnight is feeling too hot.

So trying to find ways in which we can. Keep people cool in a sustainable and passive fashion while improving this, improving their sleep quality, improving their net use compliance could have a very large impact on the secondary effects from waterborne disease perspective. Parts of the world that have limited amounts of clean, drinkable water, yet the number one thing that we tell people to do when there's a heat wave, drink more water.

Obviously, that's going to increase now the risk of acquiring waterborne diseases, and there's some quite interesting ways in which you can actually use water that's not clean enough to drink to maybe cool the body, which then reduces the rate of dehydration, which we're investigating. And then from.

Just an incidental physical activity perspective worldwide, people using physical activity of the means to manage diseases or protect themselves against acquiring certain types of diseases. Heat exposure is going to reduce the levels of incidental physical activity that people engage in. And as that gets worse with climate change, we need to think about those types of pathways as well.

Pierre: Maybe we can move to a slightly different aspect of the conversation. Patricia, you're involved, as you said, in developing and evaluating H resilience strategies. Can you please explain how you design those strategies and what kind of evidence you have to design them and if there are any gaps that are still in this field?

Patricia: Oh, thank you. Patricia. I think, in one word, the way to design strategies is partnership. Heat is complex, solutions are complex, I'm a scientist, I have expertise in certain areas, but needs to be sitting at the table are the communities that are impacted by heat, the city governments that are investing in cooling solutions around the city.

Physicians like Oleg who can talk about what the impact is on health. Everyone needs to be sitting at the table. And so that is how we work to design heat resilience adaptation strategies. And I will say it doesn't come all from us and it shouldn't come all from us scientists. The example, for example, in Chelsea, there, that project actually came together really nicely because sitting at the table was the city had a municipal vulnerabilities planning grant and they were planning all these different cooling strategies.

White roofs, green space, reflective pavement, the community was sitting at the table, their input was around where do more vulnerable populations exist, areas where youth hung out, where there was high density of population, a lot of households with low income. And then we were the scientists sitting at the table with the physicians and the data and the maps and all the urban planning knowledge, et cetera.

So I think that is how, so I can't say that we designed the strategies, so it was a team effort to design the strategies based on what worked for the city, what is there funding for, what is the community interested in. So I think that sort of partnership, listening and collaborating and coordinating is really key for anybody who was going to do this work.

In terms of what evidence do we have about types of adaptation interventions. So there's plenty of work. There's a lot of work supporting the impact of things like nature based solutions, water and trees, again, things like white roofs, refractive pavements. Are. The change in temperature, there is very little actually on the impacts on health, and that is because it's hard to know if you paint a sidewalk, or you repave a road, or you paint a road, what that actually does to ambient temperature exposure for people, like all I referred to, it really will only impact people who outside or inside without the ability to cool.

And so there's actually very little in all these climate adaptation solutions, very little out there on what the impact is on health. We're doing research on that. Things like cooling centers are another very popular adaptation strategy. We actually have very little evidence on who uses them and what the impact is on health.

We did a review on this and there's a lot of accessibility studies who can get there walking and thinking about who lives where and where to place them in neighborhoods that have populations that are more vulnerable. But then the evidence kind of stops there. Nothing on numbers, people's experience of heat and when they go to cooling centers, what their health impacts might be.

And cooling centers are interested because we love talking about them as I and as solutions, but if you think about it, who wants to be at a cooling center for eight hours a day to cool down, people want to be home or at work, or wherever they choose to be. And so I think all the cooling centers are popular.

That is a gap, I would say, and does do they really work on the indoor side. Similarly, I think that there's gaps of knowledge, for example, for cooling in place, things like use of window shades, adding shades outside. What the impact of the trees are on the indoor temperature, there's gaps in that knowledge.

It's hard to measure temperature indoors if you think about having to send temperature sensors to large population that collect data about their behavior at home, etc. So there's gaps, but this is why I think the research is focused on adaptation strategies on the outdoors, like the trees and the white ropes.

But there's a huge gap on what the climate adaptation is indoors. And maybe the last thing I'll say is that's also really community specific. So again, if the solution is cooling and ability to pay bills, there is a really large population in this world that doesn't have that ability. And so we have to be creative about those solutions.

And they include things at a city level, at a house level, and at an individual level. 

Saleha: What building upon that, Holly, what can you say can be done to increase heat resilience, both in the immediate short term, but also in the longer term? 

Ollie: Sure, yeah. So I think it's, really important just to re emphasize some of the things that Patricia was saying there.

The interventions that we can introduce at the landscape level of the heat cascade they can be very effective. The trouble is that those are long term solutions. The heat wave's coming tomorrow. We can't plant trees to help people. There's things that we can do to the built environment. Again, that takes, that's a slower burner, if you will.

A lot of the work that we do is looking at. And it's not just ourselves, it's our colleagues in the thermal physiology community is we look at what people can do at the individual level to help navigate their way through extreme heat events. And one of the things that we really focus on. Is that it's understanding that the health risk actually comes by virtue of the hot person in the hot environment as opposed to just the hot environment and the reason and that sounds a bit odd when I say that but I think it's important to keep in mind because there are ways in which we can cool a person without necessarily cooling the air at least as much.

And there's a lot of focus on reducing air temperature. And of course, that's an effective way of reducing heat exposure. One thing we could do is fill the air a little less and move the air a little more. So Patricia turned up to talk about fans. I'm so glad you mentioned that. One of the side of things that we've been looking at is this notion of a fan first cooling strategy, which accepts that.

If we think about the way in which we exchange heat between the skin surface and the environment is that dry heat transfer is driven by a temperature difference between the skin and the air. And so that's predominantly why we cool down when we drop the air temperature with air conditioning. But what we could do is if we move a little more, we increase something called the convective heat transfer coefficient and it accelerates convective heat loss.

That means you get more heat loss for a given ambient temperature. So if you move air more than you say, 26 degrees Celsius, if you're using residential fans at 26 degrees Celsius, you feel the same. From a thermal comfort perspective, as you do at 22 degrees Celsius with a still air. If we then say, all right, the primary driver of air conditioning use is thermal discomfort, people can move air more, increase the thermostat set point from 22 degrees Celsius to 26 or 27 degrees Celsius, feel exactly the same.

And in a study that we published in Lancet Planetary Health last year, we estimate that at least in an Australian context, people will save about 70 percent on their electricity bills for cooling and the greenhouse gas abatement. Benefit is the equivalent to when everybody switched from incandescent lighting to led lighting from a cost benefit analysis.

That's a very attractive solution that could be scaled up a lot. But this is of course, the people who have air conditioning and we're trying to incentivize people who have air conditioning to use it less because I think we do need to focus on the fact that. It is environmentally damaging, particularly at the moment where a lot of electricity is still generated by coal fired power plants.

But for those who don't have air conditioning, we need to think about the most vulnerable, and think about what types of strategies they can use in these settings where they don't have access to air conditioning. They might not even have access to a lot of clean drinking water. I had the privilege of co leading a Lancet series on heat and health back in 2021, alongside my colleague, Professor Chris Ebye from University of Washington, Professor Tony Capon from Monash University in Melbourne.

And so through that process, we did a deep dive into the physiological evidence of different low resource, sustainable cooling strategies that people can use if they don't have access to air conditioning. And we boiled them down to around about eight strategies. But I'll share with you just a couple of them because I can't remember all eight of them.

It's in a really nice infographic that's published on the Lancet website. But this idea of skin wetting, keeping in mind that the key way in which we physiologically keep cool is that we create sweat and the sweat needs to evaporate and that keeps us cool. But if you take water, you apply it to the skin surface, That evaporates, that then keeps you cool, and it saves you from sweating as well.

That's a, and that's also a strategy that people can use without any electricity. It's also a strategy that people can use in the case of disruptions to electricity supply, which is not spoken about all that much. What do we, what do people do in a heat wave when the power goes out? This is a type of strategy that is a potential solution, or at least an option in those types of circumstances.

And then this is the idea of moving air, if you don't have air conditioning, so just using an electric fan during a heat wave. And there's been guidance from Census Seas Control in the United States, the NHS in the UK, the World Health Organization for many years, that stated that people shouldn't be using fans when the air temperature goes above 35 degrees Celsius, so about low 90 degrees Fahrenheit.

And I think the origin of that idea is that's where the air becomes hotter than your skin. And so if you're moving air, you're adding more heat to the body, but that works for a turkey in a convective oven. But unlike a convective oven, of course, it's like human sweat, or we can at least apply water to the skin surface.

And the extra airflow encourages the evaporation of that sweat, particularly in humid conditions. And that actually ends up being a net benefit. However, there are limits to which fans actually become detrimental. We just completed an RCT in a lab setting where we've had elderly participants and people with coronary artery disease exposed to these simulated heat waves in a climate chamber, and we systematically assess the efficacy of these different low resource cooling strategies on their physiological heat strains, or how much higher does their core temperature go, how much more dehydrated they become, and how much extra work does the heart has to do.

And But ideally, we want these interventions to improve those markers. But what we find in very hot, dry heatwaves, so 45 degrees Celsius and say 15 percent relative humidity, fan use greatly aggravates the rate of body heating. So it doubles the rate of which your core temperature increases. It doubles the rate of which.

You dehydrate, and it more than doubles the amount of work your heart has to do. So in those types of settings, it's clear that there are environmental limits at which fans should not be used. And then the question is, then, how do we get this information into the hands of people that need this information at the right time as well?

This is where working with Public policy organizations is really important. We're working a lot of tech solutions as well through the global heat and health information network co convened by the WMO. We had a a collaboration also with Red Cross. We had a collaboration with Google recently where we're using their new excess heat warning package.

That's on every phone to help deliver some of this information in a simple way as possible. It's translation. But actually this is an entirely different level of expertise, and I'm not an expert in that kind of structural imagination. That's why it's important that we work with people that do have an expertise in it.

Pierre: We talk about two, two different scales, almost like two different types of adaptation strategies. Maybe Patricia can tell us if we know which one is the most effective. Is it more at the personal, individual level or more at the city or country level? 

Patricia: Yeah, that's a good question. I don't know that we know the answer for which one is more effective.

I do know we need all of them. Obviously, things like country policies or state policies have a big impact. They provide carrots or sticks for landlords to, for example, upgrade homes, or things like material hardship, so things like food insecurity and energy insecurity and housing insecurity. So we do need the policies.

They take a lot of time and takes a while to get people to vote for them. At the city level. There's a lot of independent decisions that cities can make. And actually, for example, we've worked with C40. These are cities that decided, you know what, we need to tackle climate change. We need to have policies and solutions in our cities.

We can't wait for countries to catch up. And so at a city level, there's a lot of cooling solutions that can get implemented, a lot of investments that can be made for the city, for the individual, for the house. People have to vote for policies. And I think that, Be obsessed. The role that Olly really well described of what can you do individually to tackle heat in your home, your individual behavior, with your neighbor, with your older sort of family members, et cetera.

The residents have to know that heat impacts health. Even in hot countries, that's not actually common knowledge. I grew up in Mexico. It's 106 degrees in May, and it's just a fact of life. It isn't anything that anybody thinks is hazardous or is connected to health. And I think that's true for a lot of hot countries in the world.

So there's that also raised awareness and education around what is heat, what is extreme heat, what is, what are the impacts on health. It is not just heat waves. Ali also talked about this earlier. There's a whole spectrum of impacts of heat on health. And it's a spectrum. It's a continuous spectrum that increases as heat increases.

It depends on how hot it is where you grew up and what your sort of how your body is used to heat. 45 degrees to someone is different depending on what part of the world you, you live in. But again, it's a continuum. It's not that only when the temperature is high for two days above 90 percentile or however we define it, that's not, that's really the smallest part of the impacts of TDON health.

So I think maybe returning to your question is we really need them solutions at all the scales, whether it's country policy, city policy, individual behavior, individual awareness. I think we need it all. And it's different in every region of the world and for H2O. 

Saleha: Thank you, Patricia, for that, because I'm from a hot country as well.

I'm from Pakistan originally, so I understand exactly what you're talking about. I'd like to close this really insightful discussion with a sort of forward thinking question. So what should be the top priorities for heat research going forward? And how do you both envision the future of this field? 

Patricia: So I think for me, there's three areas of research of where we should be thinking.

So interventions, implementation, and policy. I guess they're the three. So I'll talk a little bit short briefly about each. So on the interventions, there's a lot of solutions, and we've talked about a lot of them here. So nature based solutions like trees, water, cooler construction materials, reflective pavements, cooling centers, heat warning systems, misting stations, air conditioning, energy subsidies.

And as we were talking about earlier, we actually have not done a good job of evaluating the impact of these on, and there's lots of researchers around the world that are working on this, but we still have very little evidence. Part of the problem is that heat impacts on health aren't captured necessarily in medical records.

There's more categories now being added to say ICD codes to be able to say, okay, this person came into the ER to the hospital for something that's heat related, but historically, we really haven't captured too much around heat and the second that, as we alluded to earlier, It's hard to actually design these studies if you put a missing station into a community like at a bus stop or in a park, how do you follow people and then find out whether that actually had an impact on reducing their core body temperature or preventing dehydration or preventing an emergency room visit.

So researchers use big, huge databases like insurance claims or medical records, look at epidemiology studies at a population level. How But these kind of, they're smaller community interventions, right? Putting misting stations at a park, for example. Those are harder to actually capture what the impacts are on health.

I think intervention research. But implementation research is really about like, how do you actually implement this in a community? Every community is unique. That means cooling solutions are not one size fits all. They have to have a voice in suggesting solutions, communities do, and then how the solutions are rolled out.

An example I can give are trees, which we all love as part of cooling strategies, and communities love planting trees, city governments love planting trees. But one big challenge is tree survival, and so by partnering with communities, an example I can give is a community organization got a grant so that in a neighborhood that had low income households, the community neighbors adopted trees.

That may sound like a trivial solution for a neighborhood where the city has resources to water trees or the residents have resources to water trees, but in a community where people are choosing to pay rent or to eat or to cool, having a subsidy that says, Hey, I'm really hot days. Can you go and put some pails of water on trees can be a really good solution to how to implement the cooling is the trees, but then keeping them alive through these community engaged solutions.

I talked about the air conditioning example with older adults and how the solution there was having a buddy program. So the older adults have someone that can help put in the air conditioner in the summer and then take it down in the winter. Because if you don't take it down, now you are stuck with really high energy bills in the winter from leaking your windows.

And then the third one is policy, which again, each community is unique, but there's lots of similarities and a lot of solutions work in vulnerable communities where maybe sometimes 80 percent of the households are rentals. You need policy to get landlords to actually invest in homes or upgrade homes as we learn about what works in communities, which are short term solutions or can be quicker answers.

Policy needs to keep up. And the last thing I'll say about policy is that we need to expand our use of up. What policies can reduce impacts on heat and health? There's a lot of focus right now on decarbonization, climate mitigation, reducing greenhouse gas emissions, and the residential building sector.

What that means is having every pool weatherized, so insulated and air sealed. And that reduces greenhouse gas emissions, it reduces energy bills, and it means that you don't have to spend so much money heating your home, also, and cooling your home both seasons. Again, in vulnerable households where the decision is about heating, or eating, or renting, that results in more money, save on utility bills, that can also then impact, for example, if you have more family members.

A household income because you didn't have to pay such a high energy bill that has an impact on health as well. So there's other policies related to food insecurity, to housing insecurity, to decarbonization and weatherization that I think we need to expand our umbrella of options that can also tackle heat and health.

So anyway, bottom line, I would say interventions, implementation, and policy is where we should head. Would you like to add to that, Olly? 

Ollie: Yeah, so I think, and this has been touched on already, is that one of the big challenges is that, I think it's why they recognize that people underestimate their own heat health risk and the heat health risk of others, and coming up with tools that are easy to understand that enable people to grasp what their risk is and how it's modified by individual level factors.

And how that then can then inform the way in which they can build their own resilience. I think that's a real area that requires further research. I touched earlier on about what is essentially the black box of the understanding of the way in which medications impact the ability to thermoregulate.

During extreme heat exposure. I think overall, I think we've just got to think about how we build resilience to extreme heat without contributing to the problem further down the line. And I think that's a really important take home message for everyone, really, is air conditioning is exceptionally protective.

But I think there is a risk of viewing it as being a silver bullet because it brings with it quite a lot of other challenges that will then ultimately be difficult to overcome. To contend with in the future, I think adopting a human centric approach in the way in which we try to build individual level.

He's resilience is really important because then it enables us to start thinking about the way in which people keep cool from a physiological and physical perspective and harnessing that in the types of interventions that we're developing. And then subsequently testing their efficacy in the long term.

And then finally, I think just want to comment on it really is a philosophical thing more than anything is this notion that people really need to figure out how to work together better. I think we absolutely need to appreciate and embrace what unique perspectives that people from other disciplines bring.

And I think this is going to be absolutely essential if we're going to develop the most comprehensive solution for these complex heat health problems that we're going to face in the future. 

Saleha: Thank you so much, Patricia and Ollie for a really insightful conversation. What I really liked about it is that not have you just highlighted The severity of the situation, but how we can all be proactive and optimistic, because I think sometimes when there are conversations about heat, it can all be like, oh, what can we do?

But it's really nice to have an optimistic, proactive conversation about this. So thank you very much. 

Ollie: Thank you.

Gavin: Thanks so much for joining us for this episode of the Lancet Voice. This podcast will be marking the Lancet's 200th anniversary throughout 2023 by focusing on the spotlights with lots of different guest hosts from across the Lancet group. Remember to subscribe if you haven't already and we'll see you back here soon.

Thanks so much for listening.