Heat Stress and Dehydration: A Growing Health Concern

As temperatures soar in the UK, heat-related illnesses are on the rise. But how much water do we really need to stay healthy? A recent analysis showed that heat-related deaths in Europe have increased by about 30% over the past 20 years, with nearly 48,000 people dying from heat-related causes in 2023 alone.

According to Alex Ruani, a researcher in nutrition science at University College London, humans can die from dehydration in extreme heat within a few days without fluid intake. In less extreme cases, chronic or severe dehydration can lead to urinary tract infections, kidney stones, and a decrease in physical and mental performance.

Despite official NHS guidelines advising six to eight glasses of water a day, a 2023 study from the water bottle brand AirUp found that 45% of British people drink the equivalent of just one glass of water per day. This needs to be increased in hot climates, during exercise, or when you’re pregnant and breastfeeding.

“The benefits of staying properly hydrated include enabling your brain to work properly, regulating your body temperature, keeping a steady and rhythmic hormone production, fomenting cell longevity, aiding proper digestion, and helping to eliminate toxins,” says Ruani.

A 2023 study from the National Institutes of Health found that people who drink more water live longer and develop fewer chronic illnesses. However, the amount of water needed varies considerably, and the body will tell you if you need to drink more and when.

“The science has never supported the eight glasses thing, if only because it confused total water turnover with water from beverages and a lot of your water comes from the food you eat,” said Dale Schoeller, an emeritus professor of nutritional sciences.

Professor Tim Noakes, emeritus professor in the Division of Exercise Science and Sports Medicine at the University of Cape Town, says there is only one rule when it comes to fluid intake: if you’re thirsty, drink. “Men are generally larger so they will need to replace more fluid on a daily basis than smaller women. Any cause of fluid loss from the body, including menstruation, will increase the fluid requirements.”

However, some elderly people may have an impaired thirst mechanism and need to be encouraged to drink more than their thirst directs. “As we get older, our sense of thirst is reduced, putting us at a higher risk of dehydration,” adds Alex Ruani.

Nutritionist Sam Rice suggests that tea, coffee, and milk all count towards your daily fluid intake, but advises against shop-bought soft drinks as they can be high in sugar. Rice also recommends drinking a glass of water with every meal in addition to what you usually drink, and checking that your urine looks light and clear throughout the day.

Another indicator of dehydration is the skin turgor test. “If you pinch a bit of skin on the back of your hand, does the skin go back down immediately after you release it, or does it stay up a bit?” says Ruani. “It may be a sign of dehydration if the skin stays up after you let it go.”