Margaret McCartney, a Glasgow-based general practitioner and a medical columnist for Financial Times, has poured cold water over the popular advice that we should drink more water.
Official advice issued by the NHS says that people should "try to drink about six to eight glasses of water (or other fluids) a day to prevent dehydration". And many UK schools also require pupils to bring a water bottle to school. But Dr McCartney said there is no high-quality evidence to support these claims, which are repeated by bottled-water companies to boost their sales.
The idea that we are all short of water is thought to derive from a 1945 recommendation that adults should consume 2.5 liters of water daily, 1 ml for every calorie consumed, though this advice has only caught on in the last decade. But the crucial part of the recommendation is usually ignored – that "most of this quantity is contained in prepared foods".
To support this "thoroughly debunked nonsense" (to use Dr McCarthy's words), campaigns such as Hydration for Health – an initiative aimed at medics to promote the drinking of water and sponsored by Danone, the French maker of Evian, Volvic and Badoit bottled waters – says "many people, including children, are not drinking enough". It recommends "1.5 to 2 liters of water daily is the simplest and healthiest hydration advice you can give".
It’s not just Dr McCartney’s opinion but according to a review in the American Journal of Physiology - as reported in UK's The Independent, dated July 13, 2011 - there is no evidence that people need to drink that much and it could be harmful by causing hyponatraemia (low salt levels), water intoxication and even death. Long-distance runners who become so worried about drinking enough that they overdo it are at particular risk.
This injunction has become so exaggerated that people who follow the above official advice to drink more water may even do themselves harm, insists Dr McCartney. She has harsh words for the Water is Cool in School campaign; their aim to persuade children to replace sugary drinks with water is commendable but it goes too far when they claim mild dehydration – the sort people experience when they are thirsty – can result in a decline in mental performance.
I definitely don’t drink more than three glasses of water a day! [Beer doesn't count, does it?]. And I seem to be okay so far!!