How does water toxicity occur in extreme situations?

[CausativeAgent]

My teacher used a couple examples of real life water intoxication and his description of these evensts left me a little confused.

One event he mentioned was a marathon on a cloudy, cold day where the runners were drinking despite the fact that they weren't sweating. My understanding was that sweating actually increases your chances of water toxicity because you lose electrolytes, thus lowering your body fluids' osmolarity.

Another event was the recent death of a women who entered a contest where the participants have to drink a ton of water and not urinate (dumb, I know). In this case he mentioned that it had to do with the fact that she was holding her bladder, wherease I would've thought that part of the story would not affect her risk of water toxicity.

Am I missing something here or do these examples actually kind of miss the point when explaining this condition?

 

[dmoravec]

Well, in both cases the water intoxication stems from the dilution of the electrolytes in the body. In the first case water was added to the system and some of the electrolytes were removed, thus diluting the electrolytes.

In the second case (the recent holding wee for Wii contest) I would imagine it was just much more of a straight dilution problem than a full bladder. By having a full bladder the contestant's body was not able to dump any of the water in there, which would make it stay in the body and dilute the electrolytes.

 

[Moonbear]

My teacher used a couple examples of real life water intoxication and his description of these evensts left me a little confused.

One event he mentioned was a marathon on a cloudy, cold day where the runners were drinking despite the fact that they weren't sweating. My understanding was that sweating actually increases your chances of water toxicity because you lose electrolytes, thus lowering your body fluids' osmolarity.

Another event was the recent death of a women who entered a contest where the participants have to drink a ton of water and not urinate (dumb, I know). In this case he mentioned that it had to do with the fact that she was holding her bladder, wherease I would've thought that part of the story would not affect her risk of water toxicity.

Am I missing something here or do these examples actually kind of miss the point when explaining this condition?

This was recently discussed in a thread in General Discussion (I'll look and see if I can find it again...it was brought up because of that latter contest you mention). I posted references to some studies on triathlon competitors that provide more insight into what is going on.

In those studies, they determined that sweating makes no difference in loss of electrolytes. In athletes without "water toxicity," the amount of electrolytes lost was minimal, especially relative to the water loss, so they actually have an increase overall in electrolyte concentrations. The athletes with the greatest loss in weight (i.e., water loss) were among those with the best finishing times, so that didn't adversely affect performance.

The problem is actually not at the level of bladder function, but at renal (kidney) function. In one of the studies, an athlete who did not heed advice to drink sparingly during the race and who overconsumed water was unable to void until diuretics were administered in spite of having actually gained weight during the race (due to excessive water consumption). The athlete was also reported to appear "puffy" at the end of the race, indicative of excessive fluid in the tissues, so the excess fluid was not all in the bladder.

In the latter case, based on the studies in athletes, I would suspect the problem wasn't that she was holding her bladder, but more the other way around...she was able to win the contest because, unlike those with normal physiological functioning of the kidneys, when she overconsumed water, her kidneys stopped producing urine, so her bladder never filled as fast as the other competitors.

What none of the studies I've come across have addressed is whether cases of water intoxication are really due to the rate of water consumption (in the latter example, she was consuming water at the same rate as the other contestants), or if it is due to an underlying renal dysfunction that only becomes evident/symptomatic under situations of high stress to the body (either the physical stress of running a marathon, or the psychological stress of entering a radio competition), or possibly in reaction to excessive water consumption pushing the kidneys beyond their ability to function. The response appears paradoxical to what you would expect based on normal homeostatic mechanisms.