There’s never been a case of a runner dying of dehydration on a marathon course

Monday, February 25th, 2019

What to drink during exercise, and how much, is an ongoing debate among athletes and health professionals:

While daily water-intake recommendations vary (the National Institute of Health suggests that men consume three liters per day and women 2.2 liters), athletes are invariably told to drink at every opportunity. This hydration preoccupation — often prompted by science of limited rigor and fueled by marketing from sports-drink companies — has lead to people drinking even when they’re not thirsty, especially when working out. And according to Aschwanden, that could be a big problem. “The body is highly adapted to cope with losing multiple liters of fluid,” she writes.

In fact, the evidence cited in her book shows that drinking too much water poses a much greater risk than drinking too little. Overhydration can lead to blood-sodium levels becoming diluted to dangerous and even fatally low concentrations (a condition known as hyponatremia). This became a recurring problem, for example, at the Comrades Marathon — a famous 90-kilometer race in South Africa — after it added water stations for the first time in 1981. “There’s never been a case of a runner dying of dehydration on a marathon course,” recounts Aschwanden. “But since 1993, at least five marathoners have died from hyponatremia that developed during a race.” Drinking when thirsty, she advises, is the much better approach than wrought water consumption.


  1. I reviewed a book making this argument in 2012, but I first became aware of it nearly ten years before that, when I was talking with the park rangers who work at the Grand Canyon, and they told me the same thing: they almost never needed to treat someone for dehydration in the park, but overconsumption of water was a common occurrence.

  2. Kirk says:

    I’m gonna hold up my hand and say “Wait a minute…”, here.

    Dehydration is a rare cause of death, it is true, but the issue is that what’s actually happening is that the victims are dying of heat-related causes due to their bodies not being able to cope with the heat, which is often related to not being hydrated enough.

    In other words, before dehydration shows up as causative to death, the casualty overheats and that’s what gets recorded as the cause of death, making it look like dehydration had little to do with it. Reality is, the two are closely related–Run an un-acclimatized body out of water in hot weather, and the resultant heat injury isn’t going to manifest as a dehydration problem, but it actually is interrelated.

    Hyponatremia is more common than people realize, but the result of not having enough water in your system is often a heat injury. You would be absolutely astonished at how quickly that can creep up on you in really hot weather, and just how narrow the balance can be. The Mojave Desert or Kuwait, I’ve lived in that crap long enough that my idea of what “hot” is has been forever recalibrated, and I can tell you from having had to observe and treat a bunch of heat injuries over the years that the lack of hydration usually isn’t apparent until well after the heat injury occurs–And, that the causative agent is the lack of water in the victims system. The body will tend to cut down on sweating when it perceives that water isn’t sufficient–Or, so I’ve observed. The balancing act is critical, when you get out to the margins. If you’re out working in the noonday sun when it’s 120 degrees in the shade, you can watch yourself essentially cease to sweat copiously as your hydration level drops, and then once you’ve taken in water, you begin to sweat heavily again. Ignore what’s going on, and a heat injury won’t be far behind. Learning the limits, and acclimatization is key–The neophyte to really hot weather won’t be doing what is necessary, and will ignore the warning signs. Trick is to maintain that balance to where you’re trickling water into your belly at about the same rate you’re sweating it, and that you’re not dumping a liter or two of ice-cold water into your system all at once–That’s a recipe for nausea and trauma.

    The deal about hot tea and other warm beverages in the heat isn’t entirely wrong–I think that your hydration needs should be met by something close to body temperature, and that while you can get some cooling effect with a cold beverage, the impact on your innards ain’t optimal. These are hard lessons to learn–Ice-cold water is something you really have to manage carefully, because too much too quickly can really mess up your day.

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