Feeling foggy headed? Confused? Exhausted? As temperatures soar, many of us find we’re suddenly inept at tasks we normally find easy.
And with the UK hotter than the Caribbean this weekend, scientists are saying it is time we started to take the effect of heat on our brains more seriously.
‘Heatwaves have a significant impact on mental health,’ Dr Laurence Wainwright, an expert in environmental health from the University of Oxford, says.
‘Key areas of the brain – especially those responsible for cognitive tasks – are impaired by heat stress.’
With the UK hotter than the Caribbean this weekend, scientists are saying it is time we started to take the effect of heat on our brains more seriously. (Above, people on Brighton beach in East Sussex on Friday)
Dr Wainwright also warns of the increased risk of depressive symptoms, anxiety and, disturbingly, violent attacks during periods of extreme heat.
And Professor Trevor Harley, a psychologist from the University of Dundee, who is an expert on the behavioural effects of weather, says: ‘When the external temperature rises above 25C, the brain struggles to compute complex tasks. More worrying is the increased risk of suicide and self-harm.’
So what about is it about the hot weather that sends our brains into meltdown?
WHY CONCENTRATION GOES OUT OF THE WINDOW
A wealth of research shows that key brain functions – including those involved in memory, learning and concentration – perform less well in the heat.
In the summer of 2018, researchers at Harvard University in Cambridge, Massachusetts – where temperatures hit highs of more than 36C – carried out tests on two groups of students, one studying in an air-conditioned building, the other not.
Those without air conditioning performed ten to 15 per cent worse in measures of attention, working memory and the speed they could process information.
Other studies, looking at work productivity in American and Japanese offices, have found that concentration lags when the outdoor temperature peaks.
‘The core body temperature is regulated strictly by the hypothalamus in the centre of the brain,’ explains Dr Eileen Neumann, a neuroscientist from the University of Zurich.
A wealth of research shows that key brain functions – including those involved in memory, learning and concentration – perform less well in the heat. (Pictured: Families enjoy cooling down in the sea at Bournemouth Beach on Saturday)
‘If it detects a rise in skin temperature, it sends signals to other systems in the body to take action to keep core temperature stable.
‘This includes triggering feelings of thirst and directing blood flow towards the skin surface, to stop the organs from overheating.
‘These processes use up a lot of energy, nutrients and blood flow – reserving far less for complex brain functions, such as memory and concentration.’
She adds: ‘The brain is also particularly sensitive to dehydration – even the slightest lack of fluid can affect the quality of signals sent between brain cells.’
One Israeli study found that when temperatures are above 30C, just one morning without adequate water can affect performance on a host of cognitive tests.
In extreme cases, heatstroke occurs. This is a medical emergency that happens when the hypothalamus fails to stop the body overheating and brain cells can begin to die.
‘This can happen after about 30 minutes in temperatures from 30C to 40C without adequate hydration – particularly in those who have underlying health conditions,’ says Dr Neumann. ‘Roughly one fifth of people who have suffered heatstroke have some form of long-term neurological damage.’
THE HEAT CAN TRIGGER FEARS AND DEPRESSION
What of the claims that heatwaves may trigger mental health conditions, or make existing ones much worse?
In 2020, a large-scale analysis of more than 50 studies, involving 1.9 million mental health patients across the globe, concluded that for every 1C rise in temperature, the risk of developing psychiatric illness, such as depression and anxiety, increases by 0.9 per cent.
The scientists did not only compare climates across nations, but also examined the effect of mini-heatwaves in colder European climates, including the UK.
What’s more, doctors in the US have reported seeing a significant increase in visits to emergency departments for anxiety, stress disorders and mood problems on days when the temperature is higher than average.
And in Mexico, a monthly rise of less than 1C has been linked to a 2.1 per cent rise in suicides, according to research by scientists at Stanford University.
So what’s going on?
Some scientists say it is all down to irritability caused by problems sleeping: increased sunlight in the summer months disrupts our sleep-wake cycle, increasing the risk of insomnia.
Experts are keen to warn those taking psychiatric medication of potentially dangerous risks to physical health in hot climates. (Above, a matrix sign over the A19 road towards Teesside displays an extreme weather advisory as the UK braces for the heatwave)
But far more intriguing is the idea that hot weather has a direct effect on the brain itself.
Hot weather disrupts levels of the compound serotonin, which is integral to stabilising mood and regulating sleep.
While studies show that levels of the hormone tend to be higher when the weather is very warm, this doesn’t mean that it makes us happier.
Brain scans carried out by researchers at the University of Copenhagen identified a rise in proteins that collect excess serotonin, and deactivate it.
This results in a reduction in active serotonin, creating a risk of low or unstable moods.
‘We know that even the smallest fluctuation in active levels can have a significant effect on mood,’ says Prof Harley.
SPARKS CAN FLY WHEN TEMPERATURES SOAR
Psychologists have long pondered why the number of violent crimes committed appears to rocket during heatwaves.
‘Evidence shows us that even just an increase of 1C to 2C in average monthly temperatures can lead to a five to ten per cent spike in assaults,’ says Dr Wainwright.
There are some obvious theories: people are more likely to drink alcohol in hot weather, or get easily angered by others because they feel uncomfortable in the heat.
But Prof Harley says the answer also lies with a change in our brain chemistry.
He explains that extreme heat sparks a surge in cortisol – the stress hormone released as part of the hypothalamus’s attempt to control body temperature.
Its surge triggers the ‘fight or flight response’ – the body’s natural reaction to threats that causes a racing heartbeat and increased blood flow to the legs and arms, to prepare us for an attack.
But studies show a flood of cortisol makes us more likely to engage in impulsive and aggressive behaviours.
This may also interact with disrupted serotonin to increase the risk of other symptoms, such as anxious thoughts and low mood, says Dr Harley.
One Israeli study found that when temperatures are above 30C, just one morning without adequate water can affect performance on a host of cognitive tests. (Above, Bournemouth Beach on Saturday)
THOSE ON MENTAL HEALTH MEDS SHOULD TAKE CARE
Experts are keen to warn those taking psychiatric medication of potentially dangerous risks to physical health in hot climates.
Some medications, such as clozapine and olanzapine, which are given to treat symptoms of schizophrenia and psychosis, as well as bipolar and dementia, have a direct effect on the hypothalamus.
As a result they can stop the brain being able to effectively tell when we’re too hot.
Those taking these drugs may be less able to tell when they are thirsty, putting patients at greater risk of dehydration.
Prof Harley says: ‘We should think of sun safety not just as essential for protecting the skin, but also our mental health.
‘The same rules apply for the brain: drink plenty of water, and stay out of the midday sun.’