Do you really need to drink 8 cups of water a day.

[tommy.irene]

10 October 2013 Last updated at 08:25 GMT

Do you really need to drink eight cups of water a day?

Drinking eight cups or two litres of water a day is longstanding advice. But is there any scientific basis for it, asks Dr Chris van Tulleken.

You know those ads that remind us that even a small drop in hydration levels can massively affect performance so you need to keep hydrated with whatever brand of isotonic super drink they're selling?

They seem pretty scientific don't they? Man in white coat, athlete with electrodes attached and so on. And it's not a hard sell because drinking feels right - you're hot and sweating so surely replacing that fluid must be beneficial.

Well earlier this year sports scientists in Australia did an extraordinary experiment that had never been done before (British Journal of Sports Medicine, September 2013, Current hydration guidelines are erroneous: dehydration does not impair exercise performance in the heat, Wall BA).

This group wanted to find out what happened to performance after dehydration. So they took a group of cyclists and exercised them until they lost 3% of their total body weight in sweat.

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Then their performance was assessed after rehydration with either 1) nothing, 2) enough water to bring them back to 2% dehydration or 3) after full rehydration.

So far nothing unusual, but the difference between this and almost every other study that's ever been done on hydration was that the cyclists were blind to how much water they got. The fluid was given intravenously without them knowing the volume.

[bankhaunter]

Nobody has ever discovered exactly where the idea that 8 glasses of water a day was necessary came from, whilst encouraged by those selling bottled water, gradually the myth is being exposed.

All anyone in normal health need to do is drink if they feel thirsty.

I normally fish through a hot summer's day probably drinking no more than 250ml without any detrimental effect.

[cee-dee]

It's like many other things, repeat something often enough and it becomes a "fact".

[loveabargainido]

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@cee-dee wrote:

It's like many other things, repeat something often enough and it becomes a "fact".

---

as well practised by Joseph Goebbels......

“If you tell a lie big enough and keep repeating it, people will eventually come to believe it. The lie can be maintained only for such time as the State can shield the people from the political, economic and/or military consequences of the lie. It thus becomes vitally important for the State to use all of its powers to repress dissent, for the truth is the mortal enemy of the lie, and thus by extension, the truth is the greatest enemy of the State.”

[al**bear]

The idea of 2L , came from adding up all the liquid coming out of the body daily, by sweat, P, breath & the other stuff

But they never took into accout that nearly everything you eat contains water

[rose2008-2008]

If you drink too much water it can be bad for your heart..... Just thought id put that gem as i heard it somewhere. Some water is good for flushing out toxins though from our bodies!!!.

[tommy.irene]

Drinking water plus physical activity where you breathe at a higher heart rate (ie aerobic activity like walking, jogging, swimming, biking, resistance training etc.) will ultimately lead to weight loss. Not only will you release retained water - ending the bloated and puffy feeling, but your metabolism will burn fat at a higher rate than before you started adding sufficient water intake to your diet. If you are significantly overweight (50-100lbs), you need to add more water to your diet than the minimum recommended daily amount. Some experts agree that the intake should be another 6-8 oz. of water for every 10-20 lbs overweight.

The bad news is that coffee, tea, diet drinks, alcohol, and nicotine are diuretics meaning they actually will dehydrate you. These drinks should not count as your 1-2 quarts a day of daily water consumption. If you think you maybe retaining water, try adding up to a gallon of water a day and you could lose about five to ten pounds of retained water in a few short days. I have seen people lose up to twenty in a week by ONLY adding water to their diet.

[bankhaunter]

Some water is good for flushing out toxins though from our bodies!!!.

I'm glad you said 'some water', another myth is that copious amounts of water flush out the kidneys as though they were like a U bend where a whoosh of water pushes out an accumalation of gunk.

They just don't work that way.

[bankhaunter]

The bad news is that coffee, tea, diet drinks, alcohol, and nicotine are diuretics meaning they actually will dehydrate you.

The only way that caffeine acts as a diueretic is if, after a long period of abtsinence, a large dose is consumed.

Other than that the water in the drink far outweighs any diueretic effect and that has been proven.

Personally I can't stand water and it is very rare I drink any so according to many 'experts' I should be dead by now or at least stumbling around in an advanced state of ill health.

[loveabargainido]

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@bankhaunter wrote:

The bad news is that coffee, tea, diet drinks, alcohol, and nicotine are diuretics meaning they actually will dehydrate you.

The only way that caffeine acts as a diueretic is if, after a long period of abtsinence, a large dose is consumed.

Other than that the water in the drink far outweighs any diueretic effect and that has been proven.

Personally I can't stand water and it is very rare I drink any so according to many 'experts' I should be dead by now or at least stumbling around in an advanced state of ill health.

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( with bank's permission)

The only way that  beer acts as a diueretic is if, after a long period of imbibence, an even larger dose is consumed and it gives you the gites.

Other than that the water in the drink far outweighs any diueretic effect and that has been proven in town centres up and down the country on any Friday or Saturday night

Personally I can't stand water and it is very rare I drink any so according to many 'experts' I should be dead by now or at least stumbling around in an advanced state comatoseness

(amended for personal factuals)

[jesse--l]

I prefer a drink with alcohol in it. 

[right-then-petal]

rum

[bankhaunter]

[right-then-petal]

http://yoursmiles.org/t-emb.php

[al**bear]

Banks

The amount of water in Tea, Coffee etc, dwarfs the diuretic effect of any caffeine

[**caution**opinion_ahead]

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@al**bear wrote:

The idea of 2L , came from adding up all the liquid coming out of the body daily, by sweat, P, breath & the other stuff

But they never took into accout that nearly everything you eat contains water

---

Exactly.

The idea of drinking 2L a day of water got taken up by alternative therapists and gradually spread from there. 

Some recent experiments have shown milk hydrates much better than either water or sugared drinks.  Not that you'll see that mentioned in the bottled water and sports drinks aisle of any supermarket.