Rising temperatures may be associated with poorer mental health, review suggests

Increasing global temperatures and heatwaves may be associated with poorer mental health, according to a first of its kind review.

The new research from Imperial College London suggests that increased ambient temperature, temperature variability (compared to the average temperature) and heatwaves, linked to climate change, may be associated with an increase in hospital attendance or admission for mental health disorders, poorer non-clinical mental health and wellbeing in the community, as well as an increase in suicides.

Published today in The Lancet Planetary Health, the study consolidates the previously fragmented body of research on the impacts of ambient outdoor temperature on mental health and wellbeing.

However, the researchers note that more high-quality, standardised research is required to improve our understanding of these effects, as not all the evidence was strong enough to give firm conclusions.

Led by researchers at Imperial’s School of Public Health and Climate Cares, a collaboration between Imperial’s Institute of Global Health Institute and the Grantham Institute, the study highlights the urgent need for climate action and preventive strategies.

Given climate change is likely to result in rising temperatures and more frequent heatwaves, the association the new study suggests could be concerning. Mental health disorders are already a leading cause of disease burden globally.

The study authors call for urgent evidence-based action from health system leaders and policy makers to prepare for these increased impacts, ensuring adaptation strategies are in place. The researchers note this is most crucial for individuals and communities most vulnerable to extreme heat, such as individuals with pre-existing mental health disorders.  

It's important to raise awareness of these links so that healthcare and public health systems and professionals can respond and be prepared during hot weather. Dr Rhiannon Thompson School of Public Health

Lead co-author Dr Rhiannon Thompson, Research Associate at Imperial’s School of Public Health, said, “Many people don't realise that there are mental health risks associated with heat, in addition to physical health risks. Although, when you consider some of the possible ways this could happen, like sleep disruption and increased stress, it makes a lot of sense.

Physiological changes, such as alterations in blood flow or serotonin levels, can also be impacted by high temperatures, which may disproportionately affect individuals with pre-existing mental illnesses, who, for example, may already struggle with temperature regulation due to psychiatric medication. 

It's important to raise awareness of these links so that healthcare and public health systems and professionals can respond and be prepared during hot weather, and so that we can look out for ourselves and each other during these increasingly common periods.”

The study also revealed limitations within the existing literature, such as high variability between analysed studies in the way temperature and mental health outcomes were measured, the analysis techniques used and what other variables were controlled for. These inconsistencies across the literature led to low certainty in the precise effect size, though taken as a whole, the studies still strongly indicate that rising and extreme temperatures are a grave risk to mental health outcomes.

The researchers mapped the different methodologies and metrics used across the literature, which can help guide standardised research across different global contexts in the future. The researchers also call for a comprehensive understanding of the impacts across different contexts and for vulnerable groups, including low-resource settings and regions such as South America that have been overlooked thus far.

This is yet another way that burning fossil fuels - which is raising global temperatures and the frequency of heatwaves – can be toxic for human health. Dr Emma Lawrance Climate Cares

Lead co-author Dr Emma Lawrance, Mental Health Lead at Imperial’s Climate Cares, said,

“This is yet another way that burning fossil fuels - which is raising global temperatures and the frequency of heatwaves – can be toxic for human health. Climate action can be mental health action. The mental health of communities will benefit from action to rapidly phase out fossil fuels and support resilience to ongoing climate change, including measures such as increasing tree cover in cities, improving building standards and strengthening mental health systems.

There is sufficient evidence for policymakers to act. However, the true extent of the impacts are unaccounted for due to missing information in many global settings, such as the whole of South America, and large variation in current methods and metrics. By mapping this variation, we hope this paper will help researchers create and use more standardised approaches and encourage funders to support research in the many settings missed to date. In doing so we can better understand, monitor, and respond to the true ways that temperature affects mental health.” 

Without action to mitigate climate change and build resilience in infrastructures, health systems and communities, the researchers worry that the anticipated rise in ambient temperatures could intensify negative impacts on mental health outcomes.

Dr Friederike Otto, Senior Lecturer at the Grantham Institute – Climate Change and the Environment at Imperial College London, said, “This research has shone a spotlight on the lesser-known mental health impacts of heatwaves, highlighting why it is so important that governments take steps to prepare for heatwaves. These include preparing heatwave management plans, ensuring and testing they are implemented, informing the public about imminent heatwaves, and protecting people who are vulnerable to the impacts of heatwaves.

Heatwaves and other extreme weather events will only become more intense as the world continues to burn fossil fuels. Phasing out fossil fuels as quickly as possible will reduce the severity of future heatwaves and save lives.”

‘Ambient temperature and mental health: a systematic review and meta-analysis' by Thompson & Lawrance et al. can be read in The Lancet Planetary Health.