Drink to thirst? A paradigm shift

Its June 29th, 2013, just after 8pm in Aubern, California; its been a swelteringly hot day with temperatures of 39°c and little shade. We’re waiting at the finish line of the Western States Endurance Run, on the second hottest day in race history. Athletes have battled stiff competition, 40,000ft of elevation change and blistering heat to make it to the finish line.

Timothy Olsen, ultra-marathon running legend, rounds the corner onto the track to win this race for a second year running, in a sensational time of 15hr 17. He looks elated, knackered and dehydrated; he will have likely lost a lot more than the ‘2% dehydration’ fabled to impair performance1. So why do the athletes who lose the most weight tend to finish the fastest?

That was how I wanted this article to start, before I went on to explore the science behind it all. But fast forward to IM Frankfurt last weekend where we saw the tragic death of a British man due to ‘swelling of the brain likely caused by insufficient salt intake’. This is a tragedy, and my heart goes out to the family and friends of this man who succumbed to a condition athletes should not be suffering from in this modern day and age.

But was insufficient salt intake really the problem? We’ve seen several paradigm shifts in hydration advice in the past few decades, starting with industry forcing the idea that we must drink before thirst and drink as much as we can to stop thirst form ever happening.

This advice was closely followed by many endurance athletes becoming very unwell during and after races, and raised concerns about hyponatraemia: below-normal plasma sodium levels. The problem at stake here is that when sodium levels in the blood become very low, water enters brain cells, causing the brain to swell inside it’s rigid box, which can lead to a chain of deadly events.

So the knee-jerk reaction by industry was to tell us all to use sodium supplementation. Makes sense right?

But what have we actually seen is quite different: the most sodium you consume, the more you weight at the end of the race. However, those who are hyponatraemic are the athletes who tend to gain weight (or not lose weight). So there is a disconnect between taking sodium and developing hyponatraemia. In fact, many cases have been seen where symptomatic hyponatraemia has been seen following ‘excessive’ sodium supplementation.

Sodium intake stimulates thirst, for which you drink, and thus exacerbate the problem.

Current research suggests proper hydration can be maintained during exercise when thirst is used to guide fluid intake2, and avoiding overhydration is the most important means for preventing hyponatraemia in hot conditions3.

Perpetuating the myth of the need to beat dehydration by beating thirst is deadly advice, to which we have already lost too many people.


Thirsty? Drink

Craving salt? Eat something salty.

Feeling bloated? Stop drinking.


Will that work?


Bibliography

  1. Barr SI. Effects of dehydration on exercise performance. Can J Appl Physiol 1999;24(2):164-72.
  2. Bennett BL, Hew-Butler T, Hoffman MD, et al. Reply to: Is drinking to thirst a prudent guideline to avoid hyponatremia? Wilderness Environ Med 2014;25(4):493-4.
  3. Hoffman MD, Stuempfle KJ. Sodium Supplementation and Exercise-Associated Hyponatremia during Prolonged Exercise. Med Sci Sports Exerc 2014.

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