Hyponatremia: Swimming in a Saltless Sea.

As one can imagine, Nov. 6th being just around the corner, runners everywhere are putting the finishing touches on their pre-marathon conditioning (that is, if they haven’t injured themselves in the process). Those who’ve been lucky, determined, or smart enough to survive this far have yet another obstacle to overcome, albeit on race day.

H 2 Woes.

According to most sport scientists, the thirst mechanism should set the pace for sating of thirst – meaning, if you’re thirsty, you’ve already begun to dehydrate, get some water, fast! Putting limits on the amount of water racers are recommended to consume will probably result in some significant performance impairment, since dehydration severly impairs performance (some 5% for each 1% dehydration). However, this is a marathon, and a marathon situation (particularly on a hot day) is the perfect situation for hyponatremia to occur.

Hyponatremia is a potentially life-threatening condition where the concentration of electrolytes in one’s body fluid is so low, water flows uncontrolled into the cells from the vascular system. In other words, your cells are swimming in water. One minor side effect of this condition is that tissues and organs swell as well. While most of the cells in the body tolerate mild swelling pretty well, the brain does not, since it’s so tightly packed to begin with. The most common cause of death from hyponatremia is cerebral edema (swelling of the brain).

Marathoners and other super-endurance athletes are particularly susceptible to hyponatremia because they sweat a great deal (due to the sheer length of the exercise bout). Human sweat, just like internal body fluid, contains both water and electrolytes (sodium). However, the concentration of electrolytes is far higher in sweat than in body fluid, so as a runner sweats, his internal electrolyte concentration decreases. This is further compounded by replacing the lost fluid by drinking water, but neglecting to replace the lost electrolytes. Given that a marathoner will easily drink a couple of gallons of water throughout the course of a race, it’s not too far of a stretch to see how hyponatremia (extreme electrolyte dilution) can occur.

Glum? Yes, but it’s the reality. Every year there are at least several reports of marathoners dying from hyponatremia, but this usually occurs on hot weather days. In addition, more runners are being educated on the dangers of hyponatremia and volunteers offer salty snacks like pretzels to help the competitors replenish their electrolytes. But while the chances of a hyponatremia case are slim for Sunday, it always seems to happen. So in some ways, it’s good to see the race organizers lookng out for the well-being of the runners. But, instead of restricting water intake, couldn’t they recommend taking in more salt? Or better yet, make Gatorade available as drink of choice (cough cough corporate sponsorship).

So I hope you’ve got that – on race day, replace electrolytes by eating salty snacks, power gels, or the like, and don’t drink 3 gallons of water at a time. Good luck!

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