Exercise-associated hyponatremia

In addition to this personal blog on ultrarunning,  I also maintain a professional blog on the website of the medical journal: Endocrine Today.  Occasionally, my personal and professional interests intersect and I get to write a post about extreme endurance activity from a medical perspective.

I recently wrote a blog post at the Endocrine Today site reviewing the causes and treatment of exercise induced hyponatremia from a physiologic and medical perspective

For many years, at least through the 1960s, runners were advised to not consume any or very much water during runs. As the negative effects of dehyration were realized, the pendulum sung the other way and runners were encouraged to "Hydrate! Hydrate! Hydrate!" without understanding that it might be possible to get too much of a good thing.

It wasn't until the mid-1980s and several deaths during and after marathons and ultramarathons that the potential dangers of too much fluid intake were recognized. Taking in more water than can be excreted results in hyponatremia or lowering of blood sodium (ie salt). In it's mildest form, exercise induced hyponatermia results in bloating, swelling and frequent urination. At it's worst, severe hypontremia can cause confusion, seizure and even death.

At first medical personell were unaware of the dangers of hyponatremia.  When a runner was confused or collapsed, they automatically  gave them intravenous fluids, assuming -incorrectly- that they must be dehydrated. After several deaths, it was realized that the IV fluids actually cause more harm than goodin many cases. Indeed, the IV fluids may have been the direct cause of several deaths by worsening the overhydration and hyponatremia.

Despite how well-informed runners now may be about the dangers of over-hydration and low blood sodium, I am surprised how many medical personel at races do not understand the implications of exercise-induced hyponatremia and how to manage correctly.

We must remember however, that most of the EMTs and other medical staff at races are not runners or endurance athletes themselves.  

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2 responses

  1. Excellent point, about EMT workers etc. We assume someone collasping after excersis has dehydrated onself. Another reason why getting a person to replace fluids by mouth if at all possible is a better plan…
    Nice!

    July 8, 2009 at 6:33 am

  2. Thanks!
    I've gotten into arguments with medical staff at various events about this and other issues. They see me as just another runner, and a slow one at that. Much of the physiology surrounding extreme endurance exercise is complex, even confusing.
    However, reciting a belief such as "Hydrate! Hydrate! Hydrate!" just because it is conventional wisdom does not always mean it is true.

    July 8, 2009 at 5:36 pm

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