How heat disrupts our mental health (also)

• Visits to hospital emergency rooms increase by at least 10% on days when temperatures reach or exceed 5% above normal, according to our partner The Conversation.

• This rise in temperatures can aggravate the symptoms of people with mental disorders, and there is a link between high temperature and suicide attempts.

• This analysis was conducted by Laurence Wainwright, interdisciplinary lecturer and Eileen Neumann, associate researcher in Neuroscience.

Heat waves have a huge impact on our physical and mental health.

Doctors usually dread them, as emergency rooms quickly fill up with patients suffering from dehydration, delirium and fainting…

Recent studies indicate an increase of at least 10% in hospital emergency room visits on days when temperatures reach or exceed the upper 5% of the normal temperature range.

And some people are more vulnerable than others.

Impacts in case of mental disorders

Heat waves, as well as other weather events such as floods and fires, have thus been associated with an increase in their symptoms in people with depression and in those affected by generalized anxiety disorder – a disorder in which people feel anxious most of the time.

There is also a link between daily high temperature and suicide and suicide attempts.

It can be said that, in general, for every 1°C increase in average monthly temperature, mental health-related deaths increase by 2.2%.

Relative humidity spikes also lead to an increase in suicides.

Humidity and temperature – both of which are increasing due to human-induced climate change – have both been linked to an increase in manic episodes in people with bipolar disorder.

This phase of the disease is particularly damaging and can lead to hospitalization for psychosis as well as suicidal thoughts.

Consequences on processing

Other problems are posed by the fact that, in the event of strong heat, certain treatments can have several types of dramatic side effects:

• The effectiveness of important drugs used to treat psychiatric illnesses may be reduced;

• Many medications increase the risk of heat-related death.

  This is for example the case of antipsychotics, which can suppress the feeling of thirst and lead to dehydration;

• Others act differently depending on the person's body temperature and degree of dehydration.

  This is the case with lithium, a very powerful and widely used mood stabilizer frequently prescribed to people with bipolar disorder.

​Consequences even in the absence of previous mental disorders

Heat can also affect mental health and the ability to think and reason in non-mentally ill people.

Research clearly shows that areas of the brain responsible for processing and solving complex cognitive tasks are impaired by heat stress.

A study of Boston college students found that those who were in rooms without air conditioning during a heatwave scored 13% lower than their peers on cognitive tests.

They also had a 13% slower reaction time.

Being cloudy in the heat can have other consequences.

This is then more likely to lead to frustration, which, in turn, can lead to more aggressive behaviors.

There is strong evidence linking extreme heat to an increase in violent crime: a mere one or two degree increase in ambient temperature can result in a 3-5% increase in assaults.

The consequences are not anecdotal.

By 2090, it is estimated that climate change could cause a 5% increase in all categories of crime globally.

The reasons for this rise involve a complex interplay of psychological, social and biological factors.

For example, a brain chemical called serotonin which, among other things, helps control levels of aggression, is affected by high temperatures.

Hot days can also exacerbate eco-anxiety.

In the UK 60% of young people surveyed said they were very worried or extremely worried about climate change.

Over 45% of respondents said their feelings about the weather affected their daily lives.

Our "HEAT" file

There's still a lot we don't understand about the complex interplay and feedback loops between climate change and mental health – especially the effects of heat waves.

But what we do know is that we are playing a dangerous game with ourselves and the planet… Heatwaves and their effects on mental health remind us that the best thing we can do, for ourselves and future generations, is to act on climate change.

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This analysis was written by Laurence Wainwright, interdisciplinary lecturer at the University of Oxford (England) and Eileen Neumann, associate researcher in Neuroscience at the University of Zurich (Switzerland).

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• Health

• Climate change

• Mental Health

• Suicide

• attempted suicide

• Heat

• Heat wave

• Emergency room