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The Serious Problem of Overhydration in Endurance Sports….Really?

Too much to drink?


Or, the “serious problem of sensational editorial in sports nutrition?”

The other day a good friend and fellow endurance athlete shared a link on the Rooted Facebook page to an interview in Outside Magazine with a scientist named Tim Noakes.  Noakes is a South African and recently published a book called Waterlogged: The Serious Problem of Overhydration in Endurance Sports.  For context I encourage you to read the interview yourself, but in essence he claims that hyponatremia, a condition caused when sodium concentration in the serum falls below a certain level, is a “serious” problem in endurance sports.

Because his arguments seemed misrepresentative of the situation of overhydration vs. dehydration in endurance sports, I did some basic research to see if I could find facts within the scientific community on exercise-associated hyponatremia.  I was able to pull up a mini literature review published by Rosner in 2007 in the Clinical Journal of the American Society of Nephroloty, as well as a few other studies in the field of EAH.

Below are some of the findings I came across.  The point of this article is not to say that Noakes is right or wrong when it comes to the reality of hyponatremia.  Can drinking too much during exercise, or any time, be problematic?  Absolutely.  Is there some risk of experiencing EAH-induced symptoms when competing in endurance sports?  Absolutely.  Based on the numbers, does this pose a “serious problem.”  Probably not.

Based on the information I was able to find that cited field-studies on hyponatremia in endurance sports, most of the analysis was done on athletes competing in long-distance events – the marathon, ultra marathons, and even long-distance ultra marathons.  Is this group of athletes representative of *most* endurance athletes, let alone most active people?  Not at all.  My concern with the Noakes interview is that the information he is promoting is not necessarily relevant to the vast majority of people who will be reading it, and thus requires a level of understanding and critical thought too few people display when reading these types of sensational health pieces.

If the net result of Noakes publishing his book and subsequently promoting it is that the average active person who reads it, not ultra-distance athletes, adopts the notion that hydration is not an important part of exercising, this is irresponsible of Noakes and anyone who promotes his message.  As a member of the scientific community with a soapbox and loud speaker, it is the responsibility of someone like Noakes to determine when his scientific findings have relevancy to the masses, then package his message in such a way that it is clearly understood by those that read it.  He should be able to discern when his book, no doubt written to be profitable, may actually be detrimental.  It appears to me that his book and promotion of it represent the type of sensational misguided pseudo-science (and sensational editorial) we see all too often today.

Here is a quote taken from a literature review on sodium in the role of hydration conducted by Sharp in the Journal of the American College of Nutrition from 2006 that I believe helps frame up the discussion below:

“Because the cases of exercise-induced hyponatremia are mostly confined to extraordinary physical efforts lasting longer than 4 hr, hyponatremia is not likely to be particularly widespread among the general population who engage in exercise lasting less than 2 hrs per day.”

Some information on drinking during exercise:

1.  The title of the article / interview in Outside contains the words “the serious problem” of over-hydration in endurance sports.  There have been a total of eight (8) recorded deaths from exercise-associated hyponatremia ever. There have been, according to one source, 66 heat-related deaths in sport since 1975. Those eight deaths from hyponatremia, though tragic, out of the thousands upon thousands of participants in endurance sports each year is hardly what I would call a “serious problem.”  Instead they represent an outlying minority with little statistical significance.  Do endurance athletes experience hyponatremia-like symptoms that may impair performance in the short term, and could they pose a risk to health?  Maybe.  Is this risk greater than the risk of dehydration?  Maybe not.

2.  Rosner cites a 2002 study of 488 Boston marathon runners who were assessed for hyponatremia.  First and foremost, he acknowledges the likelihood of tester bias within this group was very high, then goes on to admit that .6% (that’s less than one percent) of people experienced critical hyponatremia.  The rest were considered “mildly symptomatic” or “asymptomatic,” and reported feelings of nausea and lethargy – after running a marathon, mind you.

For comparison sake, in 2012, two-thousand one hundred (2,100) athletes were hospitalized or treated for symptoms of dehydration or heat-related medical conditions at the Boston Marathon.  That was out of a total field-size of 22,000 runners, equating to approximately 10% of all athletes – quite a bit higher than the .6% identified as critically hyponatremic in the 2002 study.   This 10% number was admittedly higher than normal years, due to elevated temps, when approximately 1,000 to 1,500 athletes are treated for dehydration at Boston – but this rise is even more notable.  And based on this information, in the grand scheme of things, it would seem that dehydration is the greater of the two risks. What could this number look like if athletes started entering into training or events believing that taking in fluid is hardly necessary?

3.  Rosner repeatedly cites Noakes himself in the literature review.  This leads me to believe that the study of exercise-associated hyponatremia is not extensive – one of many reasons may be because it does not pose a “serious problem” as far as science is concerned.  Of interest is that in Tim Noakes’ interview with Outside Magazine he repeatedly points to the sports drink industry for perpetuating an over-hyped message of hydration in order to sell more product.  No doubt companies often fund studies they feel will yield results that will support their products, but is Noakes immune from doing research that will help sell a commercial product that directly benefits his bottom line, namely the book he recently published?

4.  Rosner cites the greatest predictor of hyponatremia as weight gain during exercise, meaning a person has drank more fluid than they have lost in sweat.  This makes total sense to me as a risk factor, but I would assume the number of athletes that net a gain in weight during exercise represents an overzealous minority.  In the Outside Magazine interview with Noakes, he admits that he himself wrote an article in 1981 encouraging athletes to “drink as much as possible.”  A piece of advice he now stands counter to.  Go figure.

In all my time as an endurance athlete, I have never once heard such advice – and would be skeptical of anyone in the scientific community that would take such an extreme approach to human physiology.  Rather, it has always been, “try to determine your sweat rate by weighing yourself before and after exercise.  You will not likely be able to tolerate replacing 100% of what you lose during exercise, so experiment and determine how much you have to drink in various conditions.”  Seems a bit more reasonable.

Below are a few additional thoughts I had while reading Noakes’ interview.  These do not necessarily support or refute any stance on hyponatremia, but may be worth considering in the grand scheme of hydration and fueling.

1. Drinking excessively during exercise is probably not good.  But drinking during exercise is not just about fluid intake – sports drinks are designed to fuel the body as well.  Water is poorly absorbed (relative to an isotonic sports drink) in the gut, does not provide the carbohydrate needed to fuel longer or intense aerobic efforts, nor electrolytes needed to support muscle function. An endurance athlete’s performance will most definitely begin to suffer during longer or high intensity efforts (note* longer or high intensity) without fueling and hydration.

2. Keep in mind anyone can complete a workout that lasts less than 1 hour without consuming anything – water, fuel, etc. If you are drinking excess amounts for a short workout, or any workout, you will likely have problems. The average person going to the gym and bouncing on an elliptical for 30 minutes does not NEED to drink anything.  And if they have been told to drink as much as they can, that is bad advice.

3. Lot’s of things affect absorption rate in the gut. A sports drink with the right concentration of carbohydrate, salts, and maybe protein will be absorbed much more effectively than water – which will sit in the gut and could wreak havoc and may increase the risk of hyponatremia.  Worth noting is that the literature is mixed as to whether or not sodium and carbohydrate sports drinks reduce the risk of diluting plasma levels of sodium, though of the literature reviews I read, it seems to be the consensus that they do reduce the risk.

4. Noakes’ anecdote about hunters in Africa is questionable at best. Really?  How do you know these things with certainty? Seems like an opportunity to capitalize on the same “ancestral” trends as McDougall does in Born to Run, or that Paleo diet advocates do. Do you really know that hunters ran for 4 hours in the heat without drinking anything?  Maybe so, maybe not, but it sounds marketable.

5. See a study by Fink in 1995 that worked with elite 10k runners. He measured an added time of 3 minutes to their 10k run with a measured 1.5% decrease in hydration.  This leads me to believe dehydration most definitely has a detrimental effect on performance, though it does not indicate that it is more or less likely to occur than over-hydration.  Anecdotal experience in the endurance community leads me to believe that the former is more likely.

6. “Listen to your body” is pretty good advice when it comes to hydration, as Noakes advocates, but many people don’t listen to their body and forget drink during exercise because they are distracted.  Also, research has shown that you have to drink about 1.5x the amount of fluid you’ve lost during exercise to replace body fluid levels (this has been determined by obtaining data-driven measurements of fluid absorption – not asking people how they “feel”). Endurance athletes regularly lose over 1L / hour during exercise, and up to 3L / hour in heat.  So for a 2 hour hard effort lowing 1 L of fluid per hour, you’d have to drink somewhere around 3 liters to replace what you lost. This is likely impossible to do while working out, and anyone who tries to do so is asking for trouble.  But in order to minimize the amount of time it takes to rehydrate, it’s probably best to start drinking early, then continue drinking after you’re done exercising.  I strongly suspect that the performance of anyone working at or around 80% max heart rate or higher for 2 or so hours will suffer without consuming fluid, carbohydrate and salts.

For me, Noakes’ assertions are very questionable and misguided, particularly considering how they are being presented and who they are being presented to.  What is the greater risk here, that a small number of people may experience mild hyponatremia, or that if the message that “drinking during exercise is not necessary” propagates and significantly more people experience dehydration and heat-related issues than already do?

In the mean time, I offer an open invitation for Noakes to join us on a hot mountain bike ride or run in the Santa Monica Mountains.  We’ll go for four hours and conduct our own experiment.  We’ll drink 1-1.5 liters of carbohydrate-electrolyte drink per hour, he can drink nothing, and we’ll see how the other fares.


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