This question stems from a debate a friend and I are having on the dehydrating effects of caffeine. Whilst I have got him to accept (by way of several peer-reviewed studies) that the idea your average coffee leaves you less hydrated than before you drunk it is a myth, he maintains that if you were to drink nothing but double espressos you would die from dehydration.
Is he right? They might not have a very high fluid:caffeine ratio, but I still find that hard to believe. Obviously, the amount you would have to drink to keep your fluid levels up would leave your heart racing and the other nasty stimulant effects of all that caffeine, but we’re talking specifically dehydration here.
Nope. Although a double espresso is super-concentrated narsty-ass caffeine sludge, the vast majority of it is still water. In order for a diuretic to reliably dehydrate you, you need to reduce or eliminate your water consumption at the same time.
While I agree with the first part of that statement, I don’t know that I’d go so far as to agree with the second. It’s probably more accurate to say that a “natural” (that is, not artificially concentrated through preparation) diuretic found in liquid form *probably *can’t dehydrate you past the point of its own water volume, there are some freaky ass plants out there than can kill you, and I’m not prepared to go on record saying it could never happen. Coffee, no, not even espresso. Some exotic rain forest moss? Who knows. Weirder effects have been reported.
I would expect that you could take a whole bunch of diuretic *pills *and dehydrate while drinking only moderate amounts of water. I’ve done the water-pill thing. You pee a LOT, and they provide no water of their own to replace that.
Seawater also contains a rather large amount of salt. Your kidneys simply can’t filter that much salt out of what you drink. You dehydrate rapidly as your body tries to get rid of more water than you actually drank in order to reduce the salt level.
Sure, but a diuretic pill contains more concentrated diuretic than you’ll find in a beverage. (That’s the point of putting it in pill form. )
I thought so, but that’s what confused me about your statement “In order for a diuretic to reliably dehydrate you, you need to reduce or eliminate your water consumption at the same time.” If I’m drinking more water in absolute terms, but even more salt, then I would still get dehydrated, would I not?
Nitpick: “Double espresso” is simply another way of saying “two espressos” so the question is, will consuming water with 60mg of caffeine/oz result in lethal dehydration.
Caffeine is a fairly weak diuretic, and tolerance to the diuretic effect builds with exposure. There is no way to give you an absolute answer without an actual study, but if your friend and I are in a raft with nothing but espresso, I’ll be delighted if he leaves it for me. Unlike the solute load of seawater, which requires some absolute minimum of free water to clear, I’m guessing the diuretic effect of caffeine is not large enough at that concentration to overwhelm the kidney’s abililty to conserve water.
Isn’t the vast majority of seawater also water? Or is it not dehydration that’s the risk in drinking seawater?
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