It was a shock when Michael Mosley, a doctor and well-known TV presenter in Britain, was found dead earlier this month after walking in scorching temperatures on the Greek island of Symi.
But it is now one of a series of deaths and disappearances among tourists in Greece as the country experiences a powerful heatwave in early summer, with temperatures soaring above 40 degrees Celsius (104 degrees Fahrenheit).
A Dutch tourist was found dead on the island of Samos on Saturday. The next day, the body of an American tourist was found on Mathraki, a small island west of Corfu. Albert Calibet, another American tourist, has been missing since he took a walk in Amorgos on June 11. And two French women disappeared on Sikinos after a walk.
The bodies of the deceased still need to be examined to determine the exact cause of death, but authorities are warning people not to underestimate the effects of the high temperatures.
“There is a common pattern,” South Aegean police spokesman Petros Vassilakis told Reuters, “they all went for a walk amid high temperatures.”
Some scientists say what is happening in Greece is a warning sign about the impact of extreme heat on the body, and in particular on the brain, which can cause confusion, affect people’s decision-making ability and even their perception of risk.
As climate change causes longer and more intense heat waves, scientists are trying to unravel how our brains will cope.
The brain is ‘the main switch’
Research has traditionally focused on the impact of extreme heat on the muscles, skin, lungs and heart, but “the brain for me is the key to all of this,” says Damian Bailey, professor of physiology and biochemistry at the University of New York. South Wales. It is the “master switch” for the body, he told CNN.
Body temperature is regulated in the brain. The hypothalamus, a small diamond-shaped structure, acts as a thermostat. It performs a delicate dance to keep the body’s internal temperature at or near 37 degrees Celsius (98.6 Fahrenheit). When it is hot, the hypothalamus activates the sweat glands and dilates blood vessels to cool the body.
But the brain functions well over a narrow temperature range and even small changes can affect it. Many people will be familiar with a feeling of sluggishness and laziness on a hot summer day.
But as the heat increases, it can have serious consequences, including lowering fluids in the body and reducing blood flow to the brain, Bailey said. He compares the brain to a Hummer: it requires enormous resources to function.
Tests he conducted on research participants in a climate chamber, where he increased the temperature from 21 to 40 degrees Celsius (about 70 to 104 Fahrenheit), showed a decrease in blood flow to the brain of about 9% to 10%.
“That’s a big problem when you consider that there’s not enough fuel getting into an engine that’s running at top speed all the time,” Bailey said.
And it has an impact. Extreme heat can disrupt typical brain activity, says Kim Meidenbauer, a neuroscientist at Washington State University. The brain networks that normally allow people to think clearly, reason, remember and construct and formulate ideas can “go haywire,” she told CNN.
It becomes more difficult to make complex decisions, such as which path to take on a hike – a decision that sounds simple, but requires weighing several different factors.
There is also evidence that people are more likely to make risky decisions and exhibit impulsive behavior when exposed to heat, she added.
An altered perception of risk in combination with reduced cognitive function can have very serious consequences. “You’re not just talking about the fact that you might get a little too hot and you might get sunburned,” she said. “You’re talking about potentially life-threatening (situations), like making bad decisions, clouding your judgment.”
Scientists are only just beginning to unravel the range of effects heat has on the brain, not just in terms of decision-making, but also in terms of mood, emotions and mental health.
“Our understanding is actually quite minimal,” says Meidenbauer. “It’s a big unknown at this point.”
Who is vulnerable?
Some people are more vulnerable to heat than others. Older people, especially those over 65, are at greater risk because their bodies do not always thermoregulate properly. The people missing in Greece were all in their mid-50s and older.
Very young children and pregnant women are also at increased risk, as are those with pre-existing conditions, including mental health problems.
But heat can be dangerous for anyone.
In 2016, a team of scientists followed 44 students during a heat wave in Boston and found that those without air conditioning experienced a significant decline in cognitive performance.
“No one is immune to the health effects of heat,” said Jose Guillermo Cedeño Laurent, one of the study authors and an assistant professor at Rutgers School of Public Health. “Our brain is an extremely sensitive organ,” he said.
Someone who is very fit, understands the dangers and carries plenty of water is still gambling if they decide to take a walk in very high temperatures, Bailey said.
“You make bad decisions and it could cost you your life.”
How to protect yourself
There are behavioral things people can do to protect themselves and lower risk, experts say.
These include not exercising during the hottest parts of the day, but instead going during the coolest parts of the day and seeking shade where possible. Wearing loose clothing and applying ice packs to the head and neck can also help.
Drinking water is essential and not just when you’re very thirsty, Bailey said. It is important not to get to a point where the body is losing fluid faster than it can absorb it. Experts also recommend electrolyte drinks, which can help replace some of the fluids lost through sweating.
Use location-sharing apps, Meidenbauer said. “Make sure someone knows where you are.”
In the long term, regular exercise is important – provided it is not done outdoors during the hottest parts of the day – as it can help the body with thermoregulation. “The fitter you are, the more resilient you are to these climatic environmental stresses,” says Bailey.
It will take time to unravel the exact causes of death of those killed in Greece, but there is a lesson that can still be learned from the tragedies, Bailey said.
“It doesn’t matter how intelligent or how fit you think you are… if you go outside in 40 degree Celsius plus temperatures, even if you’re well prepared, you’re going to run the gauntlet.”
CNN’s Stephanie Halasz and Issy Ronald contributed to this report.
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