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For the long time I am trying to find out if the following is truth: They say that some beverages dehydrates. I heard that about tea (sometimes green, sometimes black, sometimes both), coffee, beer and more (for example coke).

How does hydration from these sorts of drinks compare to others (e.g. water)? Why do these drinks less efficiently hydrate?

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Diuretics

These drinks contain minor diuretics. Caffeine is the diuretic found in tea and coffee. Alcohol is the diuretic in beer. Diuretic substances increase the amount of urine produced i.e causes dehydration. This is often offset by the water content of mild diuretics like tea, coffee, and alcoholic drinks.

Tea, coffee, and coke

Caffeine belongs to the xanthines, and inhibits re-absorption of Na+ by cells, and increases flow rate of filtered fluid through the kidneys. This reduces water content in your body. In other words diuretics do dehydrate you, specifically caffeine will. Coffee, coke, and tea (very low doses of caffeine) are mild diuretics.

Beer

On the other hand alcohol is an anti-diuretic hormone inhibitor that inhibits arginine vasopressin.

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    $\begingroup$ OK, thanks. I wonder if the benefit from amount of fluid we get from them is bigger or smaller then the handicap of dehydration.In other words it is worth to dink them if we want to have a good drinking regime? $\endgroup$
    – TGar
    Jan 27, 2015 at 18:06
  • $\begingroup$ @TedGar That's a great separate question I guess! $\endgroup$
    – AliceD ♦
    Jan 27, 2015 at 18:59
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    $\begingroup$ As a quick guess: there isn't enough caffeine in a mug of tea to dehydrate you in any noticeable way, you would have heart complications if all you drank was coffee, and the alcohol would wipe out your liver. But I imagine there is still enough liquid retained to hydrate you, but you would be drinking much more than the equivalent water. $\endgroup$
    – James
    Jan 27, 2015 at 20:32
  • $\begingroup$ Thank you, it seems logically. And I'll try open a new question, who knows… $\endgroup$
    – TGar
    Jan 27, 2015 at 22:43
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    $\begingroup$ There's some data to show moderate caffeine intake doesn't necessarily dehydrate you, but the parameters are undoubtedly obscured by what you're doing, and what you're drinking. In terms of alcohol, i believe it was approx 10mL urinated for every 1g ethanol, though i cant substantiate that claim with a source. $\endgroup$
    – CKM
    Jan 27, 2015 at 22:49

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