I read that caffeine dehydrates you. (Yes, I’m just learning this. 
) Can this be adjusted for by drinking more water? Or does caffeine somehow prevent the body from taking in water, such that simply drinking more water won’t have the expected hydrating effect?
Caffeine is a diuretic, which means it makes you pee more. Peeing a lot without drinking a lot of fluids can have a dehydrating effect. Fortunately, coffee is 98% water. Wrt dehydration, you should be okay taking in the amount of caffeine present in coffee that is dissolved in water. Drink water or some other type of liquid with your chocolate, though, and don’t worry about it.
There is certainly a finite amount of caffeine you should have in your system. It contracts your cells, reducing their water capacity - forcing them into a dehydrated state - meaning they won’t rehydrate until the caffeine disperses. So it doesn’t matter how much water you drink if you have too much caffeine in your system. It will just pass right through.
Pan1, I’d imagine that level has to be pretty high. If you’re so caffeinated that you’re in an irreversible dehydration state, you’d be wired near to explosion levels.
**Frylock, **Drink the water, you’ll be fine. Everyone needs to drink a bit more water anyway. And if you don’t need it, your body will get rid of it.
Or…you could not worry about it, since it’s a myth, anyway:
http://www.beverageinstitute.org/healthcare_professionals/caffeine_qa.shtml
http://www.divinecaroline.com/22178/46361-coffee-makes-dehydrated--say-what-
To call it a myth is a bit blaise.
Caffeine does dehydrate, but no one really drinks enough to have a noticable effect. Of course, with all the energy shots/red bull type drinks out there now, it might be possible to do so.
I don’t know how much that top cite is worth since it’s sponsored by CocaCola. The information seems valid, but the source of the information should be looked upon with skepticism.
What’s enough? Warning: anecdote time.
When I worked at Starbuck I’d have upwards of 12 shots of fully caffeinated espresso pretty much daily (or at least every day I worked). I never found myself dehydrated. The thing to note is that my caffeine was always suspended in fluid. On rare occasions, however, I have over-caffeinated myself to the point suffering from the shakes and getting hot flashes, but that’s abuse of a stimulant, not dehydration.
What’s interesting is that most people were so fearful of my intake, I asked my doctor about it. What he told me, after asking numerous questions about my health, is that I’ve likely built up a tolerance to the drug and that I’d likely suffer ill-effects if I adjusted my regular dosage of caffeine, but that it wasn’t causing me any problems at the moment. Long term, I believe he indicated I might want to reevaluate my caffeine intake and then he told me to watch my (normal) blood pressure for cues.
The second link of TimeWinder’s list mentions caffeine tolerance with regard to electrolyte/fluid balance:
Now, my intake is considerably less, my BP is still normal, and I’m still just an anecdote, but at least Divine Caroline backs me up. 
Which is why I gave you four cites, including two (indirectly referenced) scientific studies and Snopes. If you’d like a couple hundred more, you can enter “caffeine dehydrate” into Bing or Google. If drinking a caffeinated beverage does not result in a net water loss, it’s not dehydrating. And the actual studies don’t even detect a difference in water output from caffienated beverages, much less a difference that would overcome the quantity of the liquid carrying the caffeine.
It’s a myth. Really. If you still don’t believe me, drink eight glasses of water today and measure your urine output. Drink eight glasses of caffeinated pop tomorrow and measure. It’s not the most pleasant experiment in the world, but it’s trivially easy to show that the supposed effect is false.
Don’t want to do that? Just drink purely caffeinated beverages (no water or other beverages) for a week and notice that you aren’t dead (3 days without water would be enough to seriously injure or kill you). You won’t sleep much, but your water level will be fine.
Years ago I took a flu-having friend to urgent care, and the nurse asked her if she’d been drinking liquids, then asked what kind. When she answered “tea” the nurse said that it doesn’t count because it’s caffeinated, that the caffeine completely negated the water, and she needed 8-10 glasses of water on top of the tea.
This woman was adamant that caffeinated beverages provided no hydration whatsoever. My friend replied all she drank was tea, and if that was the case she hadn’t had anything to drink in months and should be dead.
Timewinder, I kind of despise plain water and there’s too much sugar in juice. Like my friend I drink tea (iced or hot), and the occasional diet coke. I sleep fine, as I’m accustomed.
I drink nothing but Coke Zero. Plain water - rarely, not daily.
I’m not disagreeing with the fact that normal caffeine intake and even above normal caffeine intake will not dehydrate you. But it’s not a myth that caffeine dehydrates. It just doesn’t do so at a level we’d notice at usual and unusual consumption levels.
The flaw here, I think, is that what you are saying is a myth is not what I am saying is not. It’s not a myth that caffeine dehydrates. It is a myth that coffee/coke dehydrates more than it hydrates. Honestly by the time you intake enough caffeine to cause hydration problems, other problems will be more prominent.
For what it matters, when engaging in a factual argument, don’t even mention a questionable source of facts - right or wrong, the integrity of the potential biased source hinders the integrity of all of your arguments.
On a bit of a tangent here, but, anything that dehydrates you, whether a medicine, alcohol, caffeine, or whatever, always causes you to pee out salt and water, not just water. It is physiologically impossible for a person to pee out salt-free water, no matter if you’re referring to normal peeing or peeing in disease states. So, by definition, water alone is never adequate to replace urine losses.
Notwithstanding the above, in most cases, you’ll do just fine by drinking pure, salt-free water to replace urinary losses since the amount of salt lost is small. However, in cases of large and ongoing diuresis (excessive peeing), there is signicant salt loss accompanying the water loss in the urine. In such instances, taking in salt-free water alone is inadequate - you must also take some salt. If you don’t, hyponatremia, a potentially serious state can result.
The same rationale applies to extreme sweating as well. That’s why Gatorade is so popular among athletes - it contains salt.
(in this post, salt = sodium)
Here are two studies [warning: PDF] that disagree with you.
From the first link:
I bolded the relevant part. How about you pony up some cites for your assertion? I can’t find anything that indicates dehydration at the cellular level due to caffeine other than a bunch of natural health sites. Here’s something else I found out about “chronic cellular dehydration.” It’s a marketing term.
That interview may be hosted on a potentially biased site, but the article is fully cited. The interviewee is the author of one of the studies that is cited by the snopes article.
In fairness, I think pan1 is agreeing with you (and me) that there’s no net loss of water. We’re quibbling over the definition of “dehydration.”
I’d claim that if you drink something, and you end up with more total water in your system than before, that it did not “dehydrate” you.
pan1 is using the definition that drinking water + caffeine will result in you retaining less water than if you’d just drunk the water alone, and calling that “dehydration.” These are not the same use of “dehydration,” and both arguments could be correct given their respective definitions.
That said, the studies I looked at indicated they couldn’t find any effect at all, not even by pan1’s much looser standard of dehydration.
If so, it was unclear when he said:
The studies linked to indicate that it is most certainly *is *a myth.
Well, where does the fluid go then? If you take in something, you have to expel it if you aren’t going to retain it. That’s what a diuretic does. The studies are clear on this. Once again from the first study:
Caffeine is a mild diuretic in moderate to large doses for those who have not had caffeine in their system for awhile. Not so for regular coffee drinkers and those who drink caffeinated soda, tea, and a single cup of coffee.
What pan1 is claiming: that caffeine causes “cellular dehydration” is also a myth, as well.
I’m pretty sure that the SOP around here is provide cites. Especially if you’re going to criticize those cites and then contradict them. I hope pan1 is so inclined.
The problem with knowing everything I know off the top of my head is that citation becomes problematic - especially when what I know is actually incorrect.
Now I have to go lay the smackdown on my old friends who used the cellular dehydration theory when explaining why its bad that the only water I intake comes in my foods and my Coca-Cola.