The science of hydration and why eight glasses of water a day is a myth

The guidance says eight glasses of water a day is important for optimum health – but experts say the science is flawed (Getty)

Last year was the hottest year on record and all the signs are that 2024 will be even hotter. Swathes of Southern Europe are battling unseasonably hot temperatures and the Midwest and East Coast of America are seeing the mercury soar past 37C.

And with this comes new health concerns. Earlier this month the popular TV presenter and author Michael Mosley died from heat exhaustion while walking back to his accommodation on the Greek island of Symi. Four other holidaymakers have lost their lives in similar circumstances in Greece in recent weeks, several others have been reported missing while hiking or walking, and this week Sicily has been turning away tourists due to the country’s brutal heat wave.

“Generally, humans die after a few days without fluid intake,” says Alex Ruani, a researcher in nutrition science at University College London (UCL) and chief science educator at the Health Sciences Academy. “But in extreme heat where fluids and electrolytes [essential minerals, like sodium, calcium, and potassium, that are vital to many key functions in the body such as balancing blood pressure, regulating nerve and muscle function, and hydrating the body] losses are greater, death from dehydration comes a lot sooner.”