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- It's the myth that just won 't go away. Almost
- everyone thinks they don't drink enough
- water, but the idea that we all should drink
- lots of it — eight glasses per day — is based on no
- scientific data whatsoever.
- No one really knows where the eight-glasses
- idea comes from. Some blame the bottled
- water industry but plenty of doctors and
- health organisations have also promoted it
- over the decades. The source might be a 1945
- recommendation by the US National Research
- Council (NRC) that adults should consume
- 1 millilitre of water for each calorie of food,
- which adds up to about 2.5 litres per day for
- men and 2 litres for women.
- According to Barbara Rolls, a nutrition
- researcher at Penn State University and author
- of the 1984 book Thirst, this amount is about
- right for people in a temperate climate who
- aren't exercising vigorously. And 1.9 litres is
- what you 'Il get from drinking eight 8-ounce
- glasses of water — the 8 x 8 rule — as per the US
- version of the myth.
- What most people don't realise, though, is
- that we get a lot of that water from our food, as
- the NRC pointed out at the time. Foods contain
- water and are broken down chemically into
- carbon dioxide and more water. So if you are
- not sweating buckets you need only about a
- litre a day — and 1.2 litres is what you will get
- from the eight 150-millilitre glasses
- recommended by the UK's health service.
- But any talk of glasses is misleading because
- there is no need to drink pure water. The fluids
- that people drink anyway, including tea and
- coffee, can provide all the water we need, says
- Heinz Valtin, a kidney specialist at Dartmouth
- Medical School in Lebanon, New Hampshire,
- who has reviewed the evidence (Regulatory
- Integrative and Comparative Physiology,
- vol 283, p R993).
- According to the myth, however, caffeinated
- drinks don't count because they are diuretic,
- stimulating the body to lose more water than
- it gets from the drink. Not true. A comparison
- of healthy adults in 2000 found no difference
- in hydration whether they got their water
- from caffeinated drinks or not (Journal of the
- American College of Nutrition, vol 19, p 591).
- Even one or two mildly alcoholic drinks will
- hydrate you rather than dehydrating you.
- Hydrophilics respond by saying that pure
- water is better than other drinks. Even this
- claim is arguable, but the crucial point is that
- if you are a healthy individual already
- drinking enough tea, milk, juice or whatever,
- there is no evidence that swigging down water
- as well will achieve anything other than
- making you go to the bathroom all the time.
- The final aspect of this myth is that we
- need to force ourselves to drink because by the
- time we are thirsty we are already seriously
- dehydrated. Not so. Rolls showed nearly
- 30 years ago that we get thirsty long before
- there is any significant loss of bodily fluids.
- It takes less than a 2 per cent rise in the
- concentration of the blood to make us want to
- drink, while the body isn't officially regarded
- as dehydrated until a rise of 5 per cent or more.
- so relax and trust your body. Don't force
- yourself to gulp down gallons of water if you
- don't want to— that can be dangerous —just
- drink the beverage Of your choice whenever
- you're thirsty.
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