Interesting study done on the dangerous effects of drinking too much during races/endurance training. A suggestion was given in the article how to monitor yourself.

From the article:
"Bonci and Almond said a good way to prevent problems is for athletes to weigh themselves before and after training sessions. If they gain significant weight, they should cut back on water intake until they find the right balance — long before race day."

I've primarily relied on thirst alone, but ,I think I'm going to focus on the weight suggestion too. After I empty my bladder first, of course

http://www.msnbc.msn.com/id/7491948/

You can get the abstract to the actual article here:

http://content.nejm.org/cgi/content/short/352/15/1550

Of most interest: "0.6 percent had critical hyponatremia (120 mmol per liter or less)"

To get the number saying that 13% had hyponatremia they included anyone with a value of less than 135. While 134 is certainly not normal (135 to 145) it is also nothing to worry about in someone who is capable of running a marathon. 120, on the other hand, is pretty scary, but 0.6% of the population studied is not terribly significant.

If you are using thirst to decide when to drink more, I highly doubt you'd run into any problems. People who get to around 120 are force-feeding water. The study mentions that people with hyponatremia typically took in more than 3 liters of water during the race. Nobody is that thirsty.

Though I do wonder if this will cause Camelback to rethink their ridiculous "hydrate or die" ad campaign and their reccomendation to consume one liter of fluid per hour during exercise.

if you go by thirst alone, you are already in need of water, thirst is an effect of hormonal control of kidney water absorption

Though I do wonder if this will cause Camelback to rethink their ridiculous "hydrate or die" ad campaign and their reccomendation to consume one liter of fluid per hour during exercise.

Sheesh Keith, I expect more from you than this.
Did you sleep thru that class?

but 0.6% of the population studied is not terribly significant.

Exactly. I bet a lot more people die from car accidents or smoking (or maybe even lightning strikes or shark attacks - I'm being facetious).

As CB mentions, if you simply "drink when you are thirstly", you are already somewhat dehydrated, and even a relatively small loss of fluids can negatively impact performance. And last I checked, these people were doing a race.

As long as you are getting some sodium from food, fluids, or supplements (or perhaps all of the above) , then this shouldn't be a concern.

People who get to around 120 are force-feeding water.

Exactly. Somebody like me who sweats a lot (shut up CB ) can blow thru 3 liters in 2 hours on a hot or humid day, and still lose weight due to dehydration.

I've done hikes where my wife and I are both in tanks and shorts, and sweating our asses off - and then we run into other hikers wearing jeans and long-sleeve shirts who aren't sweating at all. If somebody like that took in 3L of just water, they'd have a problem. Some folks just sweat a lot (shut up CB ), and also, some folks just aren't going very hard, and therefore don't sweat much, and therefore don't need to replace fluids they aren't losing.

.

From the study:
Hyponatremia occurs in a substantial fraction of nonelite marathon runners and can be severe. Considerable weight gain while running, a long racing time, and body-mass-index extremes were associated with hyponatremia

If you are "running" a thon in over 4 hrs, then that explains why you might have this problem.

My friend drank too much water while working (digging) in the sun a few years ago.
Drank like 4 liters if I remember correctly in less than 2 hours.
Ended up in the hospital. His wife, an RN, said he came close.
He is very careful now and has had no other problems.
He started drinking more GatorAid like drinks too. Before he was a water only guy.

the problem with just drinking water is its useless to you if don't replace the Na and other electrolytes you lose from sweating