I know there was a recent case of a “water-drinking contest” where one of the contestants died. How exactly does ingesting too much water kill you? Exactly how much did she drink? If you are drinking too much water, let’s say enough to be bad for you, but not enough to kill you outright, what would your symptoms be?
Do a search on “hyponatremia.” Several marathoners - fearing dehydration - have died from drinking too much water during races, too.
I’ve actually had hangovers the next day from drinking too much water too fast immediately after running (as in more than a litre), which is why that’s not recommended.
Hyponatremia obviously means low sodium. Basically, you die from diluting the blood too much. It happens in raves and races. I assume that sport drinks are an attempt to overcome that. I think twelve glasses of water in a short span of time is dangerous.
Water tends to move from areas of lower sodium concentration to areas of higher sodium concentration. When you hit the critical dilution point from drinking to much of a hypotonic fluid (a solution with lower salt concetration than you find in regular cells of the body and blood) and your blood plasma gets all watery… the free water moves into your cells!
Wheee! So your organs start to swell up like thirsty sponges and don’t work right. When your brain starts too swell inside its hard case (your skull), bad things happen.
That’s why Gatorade and other sports drinks have sodium.
As for the amount of water that will do this… It depends. It depends on your size, whether you’re retaining water, whether you’ve been eating lots of salty foods, how often you pee, etc. I can probably safely put away a litre in a short period of time, but two might kill me. (Actually, I wouldn’t drink 1.5 litres --too risky!)
What happens if you drink the amount of water that would kill you with hyponatremia but in Gatorade?
I don’t know. There’s another thread that asks about over-diluting potassium and other stuff. So if your sodium levels don’t get thrown out of whack, possibly something else might get messed up instead.
This Straight Dope column by Cecil Adams may be of interest: Can water be too pure? Is too much water bad for you?
Wouldn’t drinking water in moderate quantities only when you are thirsty be a safe bet for laymen?
Yes, but this is how marathon runners can get into trouble. They are rehydrating out of physical necessity, but still losing sodium to sweat etc.
I often have a baggie of salted peanuts and a banana in my racing kit if I’m only drinking water. At a certain point I switch to a sports drink like Gatorade.
For most people there really isn’t that much of a reason to drink too much water (why would you?) It just doesn’t come up in any normal circumstances.
I’m going to apologize in advance, but I don’t see a good way to answer this without getting into a bit of jargon and minutiae.
Point #1: You cannot pee out pure water. Your urine must contain some salt (or other osmole (e.g. urea)).
Point #2: The minimum concentration of salt or urea, etc., in your urine is about 50 mmol/L. This represents the most maximally dilute urine you’re capable of making.
Point #3: On average, over one day, the most milliosmoles (of all types) you have available to add to urine is about 600 mOsm.
Hence, the most urine you can make in a day is about 600/50 = 12 L.
So, any intake of water beyond 12 L will at least temporarily be held onto. If a person consumes, say, 20 L of water in a day, the excess 8 L of water will be used to dilute the sodium (and other solute) concentration throught the water compartment of the body (with the water compartment being about 50% of a woman’s body weight).
So, a 60 kg woman has 30 L of water in her body. If she holds on to an extra 8 L, that will dilute everything in her body’s water compartment by 8/30, i.e. just over 25 percent. If the usual concentration of her blood sodium is 140 mmol/L, she’ll wind up with a level of 105 mmol/L (25% lower than normal). A level of 105 if suddenly acheived could well be fatal.
So…what’s the subjective experience of hyponatremia? Slow lapse in unconsciousness? Blinding headaches from the brain swelling? Hacking cough from lung fluid? How do you know it’s coming on?
To a great extent, the degree of the manifestations of hyponatremia is contingent upon the acuity of its development. So, someone who has gradually become hyponatremic over a week or two may have very little, if any, in the way of symptoms. Conversely, hyponatremia that develops rapidly, over a day or two, is likely to be associated with prominent symptoms.
The symptoms of hyponatremia are non-specific - lethargy, mild confusion, and nausea are fairly typical. More extreme symptoms might include seizures, coma, and even death.
Despite what’s been said earlier in this thread about the mechanism of hyponatremia-induced symptoms, I am not at all sure they’re due to brain swelling. By and large, the brain has ways to maintain it’s appropriate osmolality and thus water content. What is more likely to result in symptoms, and which can be permanent, is the too rapid correction of hyponatremia. This is called central pontine myelinolysis. Despite the name, any part of the brain may be affected by this process which is sometimes referred to as osmotic demyelination. See here for more details.
Marathon runners and those into heavy exercise aren’t included in my category of “laymen.” They should be aware of how much water they are drinking and what their proper amount is.
If they aren’t, well, the world has too many people anyway. 
Well, as the king of bets, I’m here to answer that one for you: Having drunk five litres in little over 20 minutes (I’m 75 kg and 193 cm), The first thing i noticed (except of course feeling quite filled) was an oncoming headache, then I got slightly dizzy. I thought it would be a gould idea to have a pinch of salt. However, the worst about it was the panic after we got the splendid idea to call poison control, and the woman in the other end just went “Oh. Oh. Ehrm… Is this your number? Can I call you back?” She also said that eating salt might not be such a good idea as it would further upset my balance (Although the main thing about drinking too much water is that it dilutes the NaCl, there are some other salts or minerals or somesuch to be careful about, too)
We rushed to the hospital, and after a blood sample and the scariest wait I’ve ever had, the doctor told me I was ok, but should have some soup before I went to bed and some more in the morning.
The hospital took more than I won from the bet, too.
Cellular edema is indeed a major factor when the drop in sodium is rapid. If the drop in sodium is gradual, the brain can adapt. Here is a link to a paper on the subject. It does not take much to cause major problems - the skull leaves no room for expansion, so even a small degree of generalized edema can cause rapid increase in intracranial pressure.
And weight gain. They had a special about this on Bryant Gumbel’s HBO show Real Sports. The doctor said they should have scales and some of the water stations during a marathon. http://www.newsobserver.com/105/story/372885.htm
Thanks for the link . . . it’s a nice one.
But, you know, I think it actually vindicates what I posted, i.e.
Indeed, the article states:
In other words, for all but acute hyponatremia, there is NO significant brain swelling. Any stmptoms are due to the hyponatremia per se.
As an aside, and with reference to a post I made in one of the many threads regarding the poor woman who tried to win the Wii by drinking lots of water, let me recap: I asserted that young women are at the highest risk, certainly more than men, and even at higher risk than those you might intuitively think are at high risk such as old people with associated heart, brain, and kidney disease, etc. Quoting from the Epilepsia article again, we find:
(emphasis added)