"Drink at least eight glasses of water daily
This is one of the most deeply entrenched of beliefs among the public ? especially the young, who often walk about with a bottle of water to avert the ever-present danger of dehydration.
But finding an authority for the claim is impossible. It is usually bolstered by a secondary claim, which is that tea, coffee or the fluid in food does not count. This is equally baseless.
The two US experts found possible sources for this claim, often repeated by bottled water companies to increase their sales. One, a recommendation from 1945, said that 2.5 litres a day was a suitable water allowance for adults. But it went on to say: ?Most of this quantity is contained in prepared foods.?
If this last, crucial sentence is ignored, say the authors, ?the statement could be interpreteed as instruction to drink eight glasses of water a day?.
In fact, they add, studies suggest that an adequate fluid intake is usually met through typical daily consumption of juice, milk and caffeinated drinks such as tea, coffee or colas.
?But drinking excess amounts of water can be dangerous, resulting in water intoxication, hyponatraemia [low salt levels] and even death.?
One academic, Heinz Valtin, of Dartmouth Medical School, New Hampshire, has tried to scotch the myth, without success. In the American Journal of Physiology he concluded that it had no basis at all. Nor is it true, he says, that caffeinated drinks do not count. They do, and so do weak alcoholic drinks such as beer, in moderation. For healthy adults living in a temperate climate leading sedentary lives ? just the kind of people never seen without a plastic bottle ? the injunction to drink more water is nonsense.
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