Heat and health - a role for genomics?

Some of us are more vulnerable than others to heat stress, particularly the long terms effects. We have been investigating evidence for taking a genomic approach

Chantal Babb de Villiers

4 December 2023


Climate change is happening now. Global average temperatures are steadily increasing and heatwaves are increasing in their frequency, intensity and duration. Worldwide, more and more of us are being exposed to extreme heat and experiencing heat stress as a result - and this is having an impact on the health of individuals and populations.

Deaths, directly and indirectly related to extreme heat, are on the rise. Evidence is also emerging of long-term consequences to our health, particularly heart health, as a result of exposure to increased temperatures and this includes even moderate increases. Researchers are only just starting to understand these long-term health consequences.

UNICEF’s aptly named report, “The coldest year of the rest of their lives: Protecting children from the escalating impacts of heatwaves”, states that 559 million children – 24% of the world’s total – are currently exposed to high heatwave frequency. Predictions are that this could rise to 2.02 billion children, over 99% globally, by 2050. The consequences for the health of this generation, and the next, make a compelling case for new investigations across the many areas of research to investigate and understand the problem – and solutions to this growing problem.    

Heat and health – a complex relationship                                                

Investigating the impact of heat on health is complex. The level of heat someone is exposed to is constantly changing. There are numerous variables that can influence a person’s heat exposure, from the clothing they are wearing, the building they live or work in, access to water and air conditioning as well as previous exposure to heat. These factors affect how someone can adapt to hot weather. Biological differences - including genetic variations - between groups and individuals also have a role.

Of course, the genetic component is only one element contributing to health  – as it is in most conditions – and agreeing ways to slow climate change, as well as the impact on health is imperative. But the consequences of climate change on our health are being felt now, and some of us are more vulnerable than others. Could a better understanding of the role of genetics help save lives and improve care in the short and longer term?

At PHG Foundation we were curious about the current landscape of genetics research related to heat exposure resulting from the climate change crisis. Having looked at other genetic research on environmental exposure such as drug response (pharmacogenomics), nutrition (nutritional genomics), and infectious disease (host genomics), we expected to find genetic research activity in the field of heat exposure. But what we actually found is that most research activity has been in animals and agricultural settings. Research looking at the genetics of heat response in humans has focused on three main areas: species adaptation to extreme temperatures or evolutionary adaptation, rare conditions linked to thermoregulation and exertional heat illness studies in military or athlete populations.

There are also studies exploring the physiological processes, such as thermoregulation -- how the body controls heat in order to maintain an optimal temperature. However, the underlying molecular basis for these responses, for example why do some adapt to temperature increases less well than others - is poorly understood. It is also worth noting that what studies there are in this area have been done on small numbers of subjects with few being repeated, a critical step in proving a scientific theory. This mainly relates to the complexity of doing heat related research.

What is a heatwave?  

To be able to investigate the genetic aspects of heat response, we need to have data on the exposures that people experience so that we can investigate what they are responding to. To successfully do research on the effect of heat on the health of populations will require integration of data from other perspectives. For example, somewhat surprisingly, there is no universal definition of heatwaves, a measure that is used by multiple disciplines pursuing heat and health related research.

The are characteristics common to most definitions, such as intensity, frequency, duration, timing, and spatial extent. Climate researchers will use specific thresholds for different locations and times to define heatwaves and thresholds are typically calculated relative to a “baseline period” or “reference period” for the specific area and these can vary according to national or institutional norms.

A more commonly used definition of a heatwave is the local 15-day average for that time of year is exceeded and is in or above the top 10% for a period of three days or more.

Another measure to consider - and one that is particularly useful when considering health is wet bulb temperatures, usually abbreviated to TW. This heat measure takes into account humidity, making it a useful way to assess the risk to human health. Humans sweat allows for cooling but sweat will evaporate more slowly in more humid conditions, which in turn slows down cooling. The use of wet bulb temperatures from a climatology and meteorology perspective has only begun recently but the importance of this measurement for human health has become clear.

Where to start?

This truly is a multidisciplinary area of research that can integrate novel technologies, learning from various disciplines, and the latest advances in data science. Longitudinal health studies are becoming more common, and these could lend themselves well to studies of long term or delayed effects from heat exposure.

As we share our new report Heat, health and human genetics there are many intersections - between climate change, physiology, the built environment and clinical monitoring - waiting to be explored by researchers concerned with the impact of heat on human health. With PHG Foundation colleagues, I expect to be pursuing our interest in this emerging field, perhaps bringing our genomics and ‘omics lens to wider exploration into this multifaceted field. 

Colleagues from across climate change, physiology, healthcare, public health, built environment, technology development and of course genomics are invited to contact us at PHG Foundation for a discussion about any of the ideas related to this blog and the report Heat, health and human genetics.

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