Expert Comment: The hidden mental health impacts of heatwaves
Ahead of the forecast high temperatures over the UK’s Spring Bank Holiday weekend, Dr Laurence Wainwright, Senior Departmental Lecturer at the Smith School of Enterprise & Environment and Senior Researcher in the Department of Psychiatry, outlines the unexpected risks.
After a dreary grey 6 months, the heat and sunshine are here at last. Temperatures over the Bank Holiday long weekend will be warm - peaking at up to 34°C in southeast England on Sunday and Monday - and likely breaking the 1922 record for the hottest-ever day in May. Because temperatures will be well above the highest normal ranges for multiple consecutive days, it is classified as a heatwave. Such temperatures are highly unusual for May – and based on everything we know the most likely culprit is human-induced climate change.
The relationship between heat and human health is complex: while overall, we are resilient and tolerant of a fairly wide range of climatic conditions, overwhelming scientific evidence indicates that extreme levels of heat, coupled with a lack of appropriate support structures to manage it, can be highly problematic for health – especially in certain subsets of the population (such as the elderly, very young, and those working in an outdoor occupation).
“While most people typically understand that heat can cause physical health problems (things like dehydration-related health risks are fairly well understood by much of the public), far fewer are aware of the mental health impacts of extreme heat and heatwaves. For the 16% of the UK population living with a mental health condition (the most common being anxiety disorders, depression, bipolar disorder, and schizophrenia), heat can pose a range of challenges – some of which can be quite serious.”
What extreme heat means for people with mental health conditions
While most people typically understand that heat can cause physical health problems (things like dehydration-related health risks are fairly well understood by much of the public), far fewer are aware of the mental health impacts of extreme heat and heatwaves. For the 16% of the UK population living with a mental health condition (the most common being anxiety disorders, depression, bipolar disorder, and schizophrenia), heat can pose a range of challenges – some of which can be quite serious.
A worsening of side effects of many commonly prescribed psychiatric medications (including some antidepressants and anti-anxiety medications, antipsychotics, and mood stabilisers) is the first problem during heatwaves. More than 10 million Britons take one or more of these medications on a daily basis. There is also a small body of evidence suggesting that heat can even slightly reduce the efficacy of a few of these medications.
Second, heat can worsen existing mental health symptoms, manifest new symptoms, and in some conditions like bipolar disorder, act as a trigger to switch into a certain phase of a condition – such as mania. While there is still much we don’t know about this impact on symptoms, heat-induced sleep problems seem to be a big factor.
Hospital admissions for mental health reasons go up during hot periods. Research shows a 10% increase in mental health-related A&E admissions during periods of sustained heat.
Sadly, there is also strong evidence that hotter periods mean an increase in suicide attempts and completions among those with a mental health condition. One study from 2018 (in US and Mexico) found a 1-2% increase in suicide rates in association with a 1°C increase in mean monthly temperature. Another study found that suicide risk doubles at 32°C versus 22°C.
Effects on the wider population
For the remaining 84% of the British population who don’t live with a mental health condition, heat can pose a range of minor to moderate challenges. Heat can cause increased levels of irritability, anxiety and stress. We all know what it’s like when we are hot and bothered: small things can trigger a disproportionate reaction, and we are sometimes quick to lose our temper.
Heat can also cause a significant decline in cognitive function (things like mental processing speed, attention, memory, and concentration) and associated productivity. For example, a 2018 study found that students in a hot room performed 13% worse than their peers in an air-conditioned room in cognitive tests and had 13% slower reaction time. Given that 35% of office space in the UK doesn’t have air conditioning or sustainable cooling alternatives, we may have a significant problem on our hands in the future.
Finally, heat can make sleeping difficult - particularly when coupled with poor quality housing. Less sleep and broken sleep are strongly linked with an exacerbation of existing mental health symptoms – or the emergence of new symptoms. The overall economic costs of sleep issues experienced by many across the UK’s population of 70 million is substantial: the UK loses approximately £40 billion each year – equivalent to two-thirds of our annual 2025/26 spend on defence.
What needs to happen next
The relationship between heat and mental health is complex, nuanced and involves intricate feedback loops between a collection of bio-psycho-social factors. We still don’t fully understand exactly what causes what, why, and how. As periods of extreme heat become more common as a result of climate change, a multi-faceted approach that brings together the scientific community, healthcare systems, governmental agencies, and importantly, those with lived experience of mental health conditions, will be required.
There is still much for us to learn. At the University of Oxford Precision Psychiatry Lab, we are currently conducting a large study to better understand the interplay between heat exposure and depression, anxiety, psychosis, and suicidality. The GALENOS project, led by Professor Andrea Cipriani, is a major international collaboration to create a continuously updated, comprehensive and trustworthy catalogue of the best scientific literature on mental health. Follow our research by clicking here.
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