Originally Posted by
MoAlpha
While virtually all heat casualties are hyponatremic to some extent, this kind of "normal" sodium deficiency has to be distinguished from water intoxication, which is what it sounds like your friend had. Drinking too much during hot weather exercise may seem unlikely, but it's a significant danger and can be deadly. Unfortunately, data I've seen suggest no reduction of risk from consumption of sports drinks instead of plain water. I still suspect sodium supplemented drinks help, but the observational data available don't pick up the signal for some reason.
There have been a number of deaths at the L.A. Marathon attributed to hyponatremia. These have typically been people who are relatively untrained and had spent upwards of 5 hours on course, likely guzzling water and nothing else.
I've felt that as long as I continue to eat as well as drink lots of water I should be protected and I am more likely to dehydrate than over-water. I've suffered terrible nausea on a few hot climbing rides and hope to not repeat that.