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51379.  Wed Feb 15, 2006 5:41 am Reply with quote

Here's an FT column I did on some dehydration myths.

<<MYTHCONCEPTIONS: Eight Glasses of Water by Mat Coward

THE MYTH: Most people in the West are chronically dehydrated. For the sake of health and beauty, we should all drink eight glasses of water every day. Only pure water will do; all other drinks are dehydrating.

THE "TRUTH": We do need to take in a certain amount of water daily - although no-one seems to know where the 8 glasses figure comes from - but we get most of it from our food. Drink lots of water, and you’ll just urinate a lot. People sometimes overdose on water, with serious and occasionally fatal consequences; even Ecstasy users have died from excess water (and not from the drug itself). There’s no scientific basis for the curious idea that fluids other than water cause dehydration. Clearly, the bottled water industry has benefited immensely from the water craze, but its origins may lie in a (US) National Academy of Sciences report of 1945 (or, in some accounts, a US Food and Nutrition Board report of the 1980s) which recommended 1ml of water per calorie of food. The Board’s conclusion that “most of this is contained in prepared foods” was largely overlooked in media reports. But why did this fad become an international obsession in the 2000s?

SOURCES: _The Independent on Sunday_, 20 July 2003, quoting Dr David Martin of Georgia State University, and others; _The Guardian_, 27 January 2003, quoting Professor Heinz Valtin of Dartmouth Medical School;;

DISCLAIMER: Some experts (such as researchers at the University of Utah, reporting in April 2003) continue to support 8-ism. FT would be glad to hear readers’ dry data or soppy ideas; you’ll find us in the pub.


63864.  Wed Apr 05, 2006 11:19 am Reply with quote

Mat, the UK Food Standards Agency, the British Dietetic Association and The World Health Organization seem pretty unanimous that we need around 3 litres of water a day.

Also, the above website (which admittedly is run by the water industry) claims that 81% of daily water intake is obtained from drinks - not mostly from food.

63869.  Wed Apr 05, 2006 11:31 am Reply with quote

I stopped drinking water altogether when I first read Mat's column, and I'm OK.

63887.  Wed Apr 05, 2006 2:04 pm Reply with quote

Also, the above website (which admittedly is run by the water industry) claims that 81% of daily water intake is obtained from drinks - not mostly from food.

That's the key, clearly - I don't think anyone disputes the approx. amoungt of water needed, but most opinion seems to be that we get it from food. Also, I think the idea that we have to get water from plain water (not beer,or tea, say) is interesting; more puritanism than science, it seems.

63910.  Wed Apr 05, 2006 5:26 pm Reply with quote

There’s no scientific basis for the curious idea that fluids other than water cause dehydration.

Fluids with caffeine in them are pretty good at dehydrating you because the caffeine acts as a diuretic, making you expel more water than your body naturally would.

63967.  Thu Apr 06, 2006 4:22 am Reply with quote

So if you drank a pint of coffee, you’d have less fluid in you afterwards than you had before? If you drank ten pints of instant coffee a day, and nothing else, would you die of thirst?

64039.  Thu Apr 06, 2006 10:06 am Reply with quote

Yes: if your body had the optimal amount of water in it to start with, then drinking a cup of coffee and urinating would remove all the water originating from the coffee, plus a little more, leaving you dehydrated.

At least, that's my understanding of the way diuretics work.

64045.  Thu Apr 06, 2006 10:25 am Reply with quote

Is the reason why you mustn't drink seawater the same as that or more maddening still?

64052.  Thu Apr 06, 2006 10:35 am Reply with quote

That raises a tricky question, then, Gray: you’re trapped on a (rather unusual) desert island; you have nothing to drink but (already mixed) instant coffee; given that the coffee consists almost entirely of water, will you die faster by drinking the coffee, or by not drinking at all?

Hey - it could happen ...

64062.  Thu Apr 06, 2006 11:18 am Reply with quote

That is a good question.

It'll certainly seem quicker because you'll be so wired that the days will just flicker by.

But I expect that the body will have some kind of lower limit beyond which it won't get rid of water in your urine, and that limit is bound to be somewhere above the level at which you start to seriously suffer in a permanent way from dehydration.

I'm willing to undergo such a test, however. Tahiti is nice, I hear.

As for seawater, it's an emetic, so you'll just throw up a lot very soon. If you manage to keep any of it down, then all the water in your body's cells will migrate to the salty concentrations by osmosis 'in an attempt' to dilute them. This will leave your cells dehydrated, and they'll basically pack up.

All sorts of nasty things start happening when your cells don't have the water they need to support the billions of chemical reactions that go on inside them - spasms, brain function impairment, liver and kidney failure...

64414.  Sat Apr 08, 2006 10:56 am Reply with quote

The “coffee dehydrates you” theory is clearly not universally accepted, to put it mildly...

“What people need to remember is that fluid is a general term and doesn't refer solely to water. Tea, coffee, squash and milk for children are all equally good fluid replacers. A lot of nonsense is spoken about water being the best way to hydrate, but it simply isn't true.”
- Catherine Collins, chief dietician at St George's Hospital, London; Independent on Sunday 20 July 2003.

“Any evidence that caffeine promotes the loss of water from the body has been greatly overplayed in recent years. It is not based on scientific fact. If you are already dehydrated and consume heavily caffeinated drinks, then there might be a very mild risk of it getting worse. But generally it makes no difference if people drink coffee, tea, cola or water.”
- Ron Maughan, professor of human physiology, University of Aberdeen Medical School; same source as above.

“Maughan and his colleagues have also looked at the effects of alcohol, considered to be another diuretic, and found that, in moderation, it too has little impact on the average person’s state of fluid balance. His results, published in the Journal of Applied Physiology, showed that alcoholic drinks with an alcohol content of less than 4 per cent such as light beer and lager can be used to stave off dehydration.” - same source.

“Though doctors don't recommend it, many of us could cover our bare-minimum daily water needs without drinking anything during the day.
"Whenever I go to the airport I see all these people carrying around bottles of water, and I wonder, 'What's behind this?' " says Jurgen Schnermann, a kidney physiologist at the National Institutes of Health. "Certainly not science."
The way it's almost always stated, in books, magazines and newspapers, the 8-by-8 rule specifically discounts caffeinated beverages, such as coffee. This is flat wrong. Caffeine does cause a loss of water, but only a fraction of what you're adding by drinking the beverage. In people who don't regularly consume caffeine, for example, researchers say that a cup of java actually adds about two-thirds the amount of hydrating fluid that's in a cup of water. That is to say, one cup of coffee equals about two-thirds a cup of water--if you're not a regular caffeine drinker.
Regular coffee and tea drinkers become accustomed to caffeine and lose little, if any, fluid. In a study published in the October issue of the Journal of the American College of Nutrition, researchers at the Center for Human Nutrition in Omaha measured how different combinations of water, coffee and caffeinated sodas affected the hydration status of 18 healthy adults who drink caffeinated beverages routinely.
"We found no significant differences at all," says nutritionist Ann Grandjean, the study's lead author. "The purpose of the study was to find out if caffeine is dehydrating in healthy people who are drinking normal amounts of it. It is not."
The same goes for tea, juice, milk and caffeinated sodas: One glass provides about the same amount of hydrating fluid as a glass of water. The only common drinks that produce a net loss of fluids are those containing alcohol--and usually it takes more than one of those to cause noticeable dehydration, doctors say.”

“surveys of fluid intake on healthy adults of both genders, published as peer-reviewed documents, strongly suggest that such large amounts are not needed. His conclusion is supported by published studies showing that caffeinated drinks, such as most coffee, tea and soft drinks, may indeed be counted toward the daily total.”
- miniurl

“ recent study in the Journal of the American College Of Nutrition revealed coffee-drinkers had the same level of hydration as those who stuck to water. ‘Caffeine does cause a loss of water but only a fraction of what you gaining by drinking the beverage,’ says nutritionist Patrick Holdord.”
- Daily Mirror, 14 October 2004.

64419.  Sat Apr 08, 2006 11:42 am Reply with quote

Well that'll be good, if we can boil it down to a statement that we're happy with - I think this does contradict a widely-held belief.

Now, Mat, if you can just produce evidence that drinking seawater is in fact good for you, I think we'll be home and dry.

71444.  Thu May 25, 2006 4:00 pm Reply with quote

“Chris Kelly, the ECB’s umpires manager, has asked all the counties to provide his men with fruit and sodium sports drinks during the tea interval. Tea and coffee are so last season. ‘We are trying to make the umpires aware that tea and coffee increase dehydration,’ Kelly said. ‘When you are dehydrated one of the first things that goes is your concentration, the next thing is your vision.’”
- Daily Telegraph, 18 May 2006.

... and thus are the Superstitions of Health built upon the Tales of the Wives of Old.

gerontius grumpus
153616.  Sun Mar 04, 2007 7:37 pm Reply with quote

Most of the effects of a hangover are the result of dehydration and hangovers are generally caused by imbibing a lot of alcoholic drinks.
But hey, alcohol doesn't dehydrate you so we'd better brush this fact under the carpet.
Pure water is not the best hydrater because the addition of small quantities of salt and glucose to water aid absorption.

Oh and why does coffee make me thirsty?

153666.  Mon Mar 05, 2007 5:24 am Reply with quote

Tea is good for hangovers (with a spoon of sugar). There does not seem to be enough caffeine to act as a diuretic, but enough to give a small jolt to get me moving. The sugar aids absorption too. Oh, and a couple of painkillers for the balsted headache!




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