Hydration myth is enough to drive everyone to drink

As temperatures rise across the globe, so do heat-related illnesses. But do you know how much water you need for optimum health? Maria Lally talks to the experts to find out

- Maria Lally

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.”

At the less extreme end, Ruani says that chronic or severe dehydration can lead to urinary tract infections, kidney stones and a decrease in physical and mental performance. Add in constipation, delirium, seizures, and a drop in blood pressure (fluid loss leads to low blood pressure, which can lead to lightheadedness and fainting) and you can see why staying hydrated can not only help avoid heat exhaustion and heat stroke but is key to staying healthy.