Who’s vulnerable to extreme heat and how can we protect them?

In Conversation With Dr Ana Bonell And Dr Matthew Chersich

According to the World Meteorological Organization (WMO), heatwave events have increased sixfold since the 1980s, driven by the naturally occurring El Nino and exacerbated by human-induced warming from greenhouse gases. Current projections say we’re 1.2oC warmer than pre-industrial levels, and global warming is likely to reach 1.5°C between 2030 and 2052. These extreme heat events are having a disproportionate impact on already vulnerable populations – including pregnant women, newborns, and children. 

I spoke with two climate and health experts, Dr Ana Bonell and Dr Matthew Chersich to discuss this further.  

Matthew and Ana, you’re both working in the field of climate change and health. Can you each start by telling me a little bit more about your background? And what led you to this field?  

Ana: My background is as a medical doctor, and I’ve taken a rather meandering career. I was interested in all sorts of medical specialties. But always with this clear indication that I was very interested in the environment from a very early age. I did my training in anaesthetics and intensive care, which gave me a very strong grounding in physiology and understanding our responses to the environment and completed a master’s in epidemiology. I went on to do my PhD looking at the impact of heat on maternal and foetal physiology, combining all my interests together and working in an area which is particularly hit by the climate crisis. 

Matthew: Like Ana, I was a medical doctor, but haven’t practised for some decades. I’m from South Africa, and initially, I worked on HIV, particularly HIV transmission in pregnant women. And then some work on maternal health and newborn health. But around seven years ago, while I was living in rural areas of Italy, I moved to study climate change and health with an emphasis on heat. And like Ana, focused on exposure of pregnant woman to high temperatures, initially looking at the impact of how heat effect affects the pregnant woman, the foetus, and the newborn. But increasingly moving towards asking, what are the solutions? How do we, how do we try and solve some of these problems and protect this really vulnerable population? 

So, Matthew, as we’ve been discussing, we’re specifically focusing on the intersection between extreme heat events and maternal and newborn health. Why are these populations particularly vulnerable to compared to others? 

Matthew: That’s a good question. And I think we should emphasise that the vulnerability of pregnant women and foetuses/newborns to heat is particularly relevant to low- and middle-income countries. In high-income countries, there’s a focus on the elderly or homeless people. We’re really talking about pregnant women in countries where there’s high levels of vulnerability, and often you have increased social vulnerability during pregnancy and diminished ability to work and to gather resources. You’re compounding some biological vulnerability as well, where during pregnancy women are much less able to dissipate heat. And often they have to continue with the current physical labour such as collecting wood or collecting water.  

I think one of the key questions is: what happens to women during labour and childbirth where there’s a very large amount of heat generated by the physical exertion of labour? And many of the facilities offer very little that protection against heat. The environment is not suitable to protect these women, and, in some places, there isn’t even water, let alone cold water. So you’re having a ten-hour ‘marathon’ with extremely high temperatures.  

To conclude, the foetus is around half a degree warmer than the mother throughout pregnancy. The foetus has no ability to regulate. And that’s a highly vulnerable period as we all know, so I think the foetal exposure is also really, really important. 

And then over to Ana, you firstly, do you have anything else to add? And secondly, to play devil’s advocate, Matthew’s just said that heat is a problem for LMICs. Is this true? Or is there any evidence to say that there is a universal global problem or will be in future? 

Ana: Yeah, to add to Matthew’s points, which I completely agree with, I think, ultimately, there is this biological vulnerability that comes with pregnancy, and specifically in terms of foetal development, but it’s very much a cultural-societal problem as well. And the intersectionality of this means that there isn’t going to be one simple solution moving forward, to take away the heat and then everything is going to be fine. As with so many other things in terms of health and the social determinants of health; poverty, the inequalities within the societies, and gender inequality plays a massive role in the vulnerabilities to the impacts of heat and the impacts of climate change.  

Ultimately, I agree with Matthew completely that the majority of women who are exposed and are extremely vulnerable to the impacts of heat are in LMICs and live in this sort of tropical/subtropical region. However, we do know that most of the large-scale environmental EPI studies, and Matthew’s done a very thorough systematic review and meta-analysis, have come from high income countries. Pretty much, I think we can now say that the evidence is very strong to show that globally, in high-income countries, as well as in low-income countries, we see this effect on pregnant women where you have an increased risk of adverse birth outcomes from being exposed to high levels of heat. I think because of the ubiquity of the exposure in certain regions, and the vulnerabilities due to other factors, yes, the most at risk women are from LMIC’s, but that doesn’t mean that the high-income women are not at risk also. 

Matthew: To pick up on that point, briefly. I think and it’s completely right, there are now, around 200 studies to show that that heat exposure, or high temperatures, or heat waves, in pregnancy are harmful to maternal and newborn health. And most of those are certainly from high-income countries. Because that’s where the large the large databases exist. And even in some countries that you consider temperate, like Sweden or Canada, which people think are traditionally cooler, they also have heatwaves which are dangerous during pregnancy. So, I think that’s a good point. 

Until recently, and maybe not even now, you might argue, and maternal and newborn health has been missing from the climate change agenda. Do you have any opinions on why you think that is?  

Ana: Because we live in a patriarchy? 

Matthew: I think that a lot of climate change has so far been focused on the Global North. And a lot of the evidence on heat vulnerability, like I said earlier, was around the elderly, or people with chronic diseases, or people who are obese etc. And even the global indicators are often around heat impacts in people above 65 years old. In Africa, the life expectancy is 65 years old. It’s clearly not a good indicator.  

So I think it’s largely because of the absence of evidence on pregnant women in low- and middle-income countries. And the fact that so much of the research has been done in the Global North. And until recently, there were only a handful of people working on heat and health in low- and middle-income countries in climate change. Whereas you had several thousands of researchers in on this topic in the Global North. And knowledge follows researchers and money, sadly. 

Ana I do want to pick up on what you said about patriarchy. I think there is something to be said for women’s health generally missing from agendas. So, did you want to say anything more about that?  

Ana: I agree with Matthew, I think probably there is a lot to do with where the research is being led. And obviously, the Global North is where the money is, and they’re the ones that get to set the agenda. But women’s health and women’s issues have been lacking for many, many years. I mean, there’s so many stark examples of this. And it’s only really coming to light that you can’t take what is found to work or be a risk factors for men and apply it to women. And so I think there is an element of that. And pregnant women are notoriously difficult to study because you have complex ethical dilemmas around any kind of interventions. People just don’t want to go there, and so with this, I think that has also happened to an extent. 

Matthew: Ana shows very clearly in her in her work in the Gambia that often, there’s this patriarchy or this totally gendered outdoor work, particularly in rural areas, where work such as agricultural, collection of firewood or of water and indoor cooking, is often really warm. Those are seen as women’s activities, and all are associated with generation of heat or heat exposure outdoors. And childcare, for example, is quite a laborious and takes a lot of energy and so on. And men often will not get involved in any of those tasks. So there’s certainly some gendered aspects around work. 

Back to Ana, you were just talking about how it can be difficult to study these populations, particularly pregnant women, and yet you have been doing a lot of work to quantify and highlight the scale of the problem. Can you talk me through the evidence you’ve generated? Both recent work that you’ve done on stillbirth and anything else that you think is pertinent today? 

Ana: Sure. This was an expert review, where we took Matthew’s previous work, and then looked at any more recent studies that have been published. And what was interesting is that there’s been a bit of a growth in studies covering this, especially studies coming from low- and middle-income countries. Now we can say that there is quite clear evidence from both high-income countries and low- and middle-income countries that there is an adverse effect of heat on the risk of stillbirth. In 19 of 20 studies we found this increased risk of stillbirth with heat exposure. The heat exposure is something that has been defined differently in different studies, so it becomes very difficult to try to get a single measure that you can say, ‘this is the threshold above which women are at risk’ and apply that to a global population. And that’s something that’s Matthew and I have struggled with in our in our work .

But the evidence base is coming together to show that it doesn’t really matter where you are, if you’re exposed to very high temperatures, wherever you are, you are at increased risk. And so that’s bringing together the global epidemiological literature showing these large-scale impacts on big databases. And our work in the Gambia is really much more small scale at the moment because we’ve been looking at the physiological response of pregnant farmers to the heat exposure; how they physiologically respond, how their foetuses respond, and exploring that in more detail to understand the lived experience of the women and what techniques they use to try and avoid the heat. We’re on the pathway to try and explore this in more detail, but we have quite a lot of extensive work coming up, which hopefully will shed some light on it. 

And this is where I’ll come to you, Matthew, because obviously, part of HIGH Horizons is trying to understand these thresholds and measuring mitigation on this global scale. But you’re also a co-lead on CHAMNHA and the work that’s going on there, which has actually built some of the foundations for the HIGH Horizons work. Can you talk through what evidence has been coming out of your work that demonstrate the risk of high heat to mothers and babies? 

Matthew: In CHAMNHA, we’ve done quite a few things, and all with interesting findings. Quantitatively, we looked at questions of heat exposure, on breastfeeding duration, for example. And we showed quite considerable decrease in duration of breastfeeding as temperature rises, and also quite interesting findings around the impacts of heat on things like pregnancy induced hypertension. So those were on LMIC databases and some of the first analysis showing that.  

In the qualitative work in Kenya and Burkina Faso, we try to really understand, like Ana was saying, woman’s lived experiences. What is it really? What does it mean to be living in very warm environments and be pregnant? And taking account of all the social determinants and other parts of their lives. And that’s really rich data.  

So that’s trying to understand the impact, but of course, as researchers, we are far more interested in: how does one intervene to lower those impacts?  

And there were two quite interesting interventional studies. In the rural area of Kenya, the Khost Province, we intervened with a small group of pregnant women who were doing a lot of outdoor labour. We tried to shift some of the cultural norms around that to change that the kind of work they were doing, or the times of day that work was being done, but also to get other women involved or men to assist with outdoor labour. So then, especially in the third trimester of pregnancy, that kind of really intense heat exposure was diminished. And those findings seem very promising.  

I think those are useful steps in CHAMNHA. They they’re single interventions, and I’m sure Ana will agree that such a complicated set of exposures and outcomes requires more intense interventions than these single simple interventions. But what CHAMNHA showed is that there’s a lot of the scope for changing practices, behaviours and protecting women. But that probably does need to be taken further with much more intensive intervention. 

It’s interesting listening to both of you about specific challenges that exist in specific communities that maybe I would never even think about, pregnant farmers, for instance. And obviously, with the interventions you bring into place, they’re going to be so different, depending on someone’s context.
So, I’d love to hear more about these interventions from both of you. What existing solutions are there? Both in terms of behaviour changes you’ve just discussed, but also what can hospitals do? Or infrastructure, those sorts of things? What do we know that already works? 

Ana:  I think actually, we don’t know very much. And that is why Wellcome made one of their priority calls last year all about heat interventions. Because the evidence base behind a lot of the things that we think of as ‘common sense’ haven’t yet been studied to have a look at whether they actually have a long-term health outcome. So although some places have put in early warning systems, for example, linking that to a maternal health outcome has not happened as yet.  

There’s some evidence from Pakistan and India, of community health workers doing some educational and behavioural interventions a bit like what Matthew’s been talking about, in terms of awareness around heat, changing work patterns, perhaps changing the timing that you do the cooking, moving from indoor cooking to an outdoor shaded area of cooking. And that has been effective in terms of like reducing the heat exposure. But to then take that a step further and link it to a hard health outcome, as far as I’m aware, is still lacking, which is why our new projects about intervention studies are so exciting. Because really, at the moment, it’s quite an unknown area. 

Matthew: And I’m a bit surprised, because there is a very simple answer to this question. ‘Air conditioning’, is the way that the Global North has answered that question. So if you asked someone who lives in Canada, America, they would have given you a one-line answer to say, ‘No, we just turn the air conditioning on’. And of course, that’s problematic. LMICs don’t have access to that. So you’re ending up with these large thermal inequities where the pregnant women are having to rely on quite simple interventions. That might be things like white reflective paint on the roof, some of these behavioural changes, perhaps we can have cool water in health facilities during labour, or perhaps a church hall that has air conditioning, so some rational use of air conditioning.  

And the built environment, of course, with nature-based solutions. So I think I might disagree with – we probably don’t have the evidence, but we have sufficient knowledge. Even though there isn’t evidence, I think there won’t be for years, or decades. We don’t have the luxury of waiting for that evidence, we really just need to move at this point. Otherwise, those thermal inequities will just increase further and further. As the temperature rises, and as the Global North just installs billions of air conditioners, you’ll just get this massive gap. And that’s just not sustainable ethically. And from a human-rights perspective and the mass migrations which will inevitably happen, no one wins by us not acting at the moment and vigorously. 

Ana: Yeah, I agree with you, Matthew, totally. I found it quite shocking. There was a paper out a couple of years ago showing millions at birth outcomes in the states linked to heat and showing an increased risk of preterm birth and the answer was that people need to use more air conditioning units. And, to me, that’s completely insane when you think about the people who are at risk. I guess my answer to that was that realistic, pragmatic, sustainable solutions maybe have not yet been completely developed. But I think, definitely, the time to act is now and ultimately we know that people need to be cooled. So how you go about doing that is what’s not known, but that is what needs to happen. 

Thinking of what you’re currently working on, is there anything that you’d like to speak about in terms of interventions? And you say about air conditioning units, but obviously, they come with a carbon cost in themselves. How important is it that the solutions are also carbon neutral? 

Matthew: One thing to highlight is that the new work is to try and look at more complex interventions, where you have multi-levels, so you might have an intervention for individual, the household, the community, and some policy intervention. So multi-level, but also multi component, trying to intervene behaviourally and in both environments, nature-based solutions and some societal solutions. And the one that I’m particularly fascinated by at the moment is some financing or cash transfer during the heatwave, and perhaps even just during the warm season. You know, some of the more interesting interventions and the more intensive interventions.  
We have what we might call ‘first-level’ interventions that that will probably manage to maintain a relatively thermal neutral environment for pregnant women at the current temperature exposures. Implemented at scale, that will probably help to reduce heat health morbidities given current temperatures, but what we need is second level interventions to cope with the temperatures that are coming in the next five to 10 years. At the moment, none of what I’m calling ‘first level interventions’ will have nearly sufficient level of effectiveness to cope with the temperatures we will shortly experience. And that’s a that’s a major problem. A sentence like that means mass mortality or major numbers of foetal and maternal morbidity and stillbirth. And that’s something I think the world hasn’t really thought through. We don’t know what to do the current levels of heat, like Ana pointed out, and we certainly have no idea what to do when it’s 55 degrees in in an urban slum in Nairobi. 

Ana: As Matthew said, our work is a little bit similar. We’re all sort of part of this new cohort from Wellcome. So we are going to be using co-design to decide on what the interventions should be. We’re planning on a cluster randomised controlled trial based in Pakistan, in both urban slum settings and rural settings, anticipating the interventions in the two areas will be quite different. But at the moment, and there will be a component, which will be structural, and hopefully, some may be nature based. But obviously, with the constraints within grants, you have only four years, so you can’t wait until the trees have grown! So we’ll do some behavioural and some community level interventions, it’s quite exciting to take it to the people who are there to get buy in from the whole community, and then see what see what comes out. 

And actually we’ve only got a couple of minutes left, and it’s a perfect time to kind of end on the question around how important is it to have co-design with the communities involved? And how are you both doing that in your work? I’ll start with you Ana. And then on to Matthew for final word. 

Ana: This study very much is co-designed (the one in Pakistan), it’s going to be completely and utterly led by community participatory engagement. During the work in the Gambia we’ve done a lot of different aspects to our community engagement. So we lead some schools’ engagement projects, where we give them the opportunity to come up with solutions for the environmental and climate related problems that they identify are important to them. And so we would like to take some of these findings forward into thinking about what sort of interventions we try out in the future. 

Matthew: You know, I think you’re asked to end on a note that perhaps is quite challenging. I understand the need for co-design, and I’m not diminishing that. But I think it comes with a lot of drawbacks, it takes a really long time. And, there’s a balance between what we know about the science and what the community feels is often going to be most effective. I think the field is all really advancing with the co-design idea. And I understand why and I’m sure that it has been effective in many fields, but equally I think there’s not enough people saying let’s go into a community, let’s do some rapid quick tests of diverse interventions at scale, and with high quality outcome measures.

So while I agree with Ana, I think this is still an unanswered question. Maybe the best approach is, given them the amount of evidence and the speed with which we need to act, to do some rapid rapid interventions and novel tests. So I’m sure what the correct way forward is.  

And maybe that’s a perfect way for us to end, with a further challenge for the research community. Thank you to both Matthew and Ana for your time today.  

You can read more about Ana’s work via her profile.