Drink Only When Thirsty When Running Or Exercising

Drink Only When Thirsty When Running Or Exercising

Here’s a simple guideline for how much water to drink when you exercise: drink only when you feel thirsty. Science Daily reports that many runners and other athletes may be drinking too much fluids when experts recommend drinking only when thirsty.

Image: lululemon athletica.

A survey found that over a third of runners were drinking according to a preset schedule or for weight maintenance, while nine per cent were drinking as much as possible. Nearly a third incorrectly thought they needed extra salt and more than half were drinking sports drinks for the electrolytes to prevent low blood sodium.

But it’s actually “drinking too much during exercise [that]can dilute the sodium content of blood to abnormally low levels”, which could potentially lead to a fatal condition called exercise-associated hyponatremia, the article say.

“The safest known way to hydrate during endurance exercise” is to only drink when thirsty, Loyola sports medicine doctor James Winger advised.

Nearly Half of Runners May Be Drinking Too Much During Races [Science Daily]


  • I realise this comes from “experts”, but I’m pretty concerned by some of this. For example:
    “And more than half (57.6 percent) say they drink sports drinks because the drinks have electrolytes that prevent low blood sodium. In fact, the main cause of low sodium in runners is drinking too much water or sports drinks.”
    While it’s true you won’t end up with low blood sodium from sweating, the implicit conclusion here that you don’t need electrolytes is clearly wrong. You still need to rehydrate, and there is some electrolyte loss through sweat (just not proportional to blood levels), so drinking straight water will imbalance electrolytes in the other direction. IF you are going to drink water (generally a good idea), it still needs to include electrolytes in proportion to what’s been lost.

    And seeing as thirst often doesn’t kick in until we’ve lost about 1-2% of bodyweight in water, waiting until that stage to begin rehydrating can be dangerous. Thirst is an indicator that your blood sodium levels are already imbalanced and you NEED water, and in the middle of an endurance run (especially if it’s hot) when you’re going to keep running and dehydrating you’re going to increase those fluid demands. What is the likelihood that someone who follows this advice is going to begin rehydrating at a rate that not just matches their continued dehydration demands as they keep running, but at a rate that makes up for the negative water balance they’re already in? Seeing as it’s quite uncomfortable to slam a large drink and keep running, most people won’t rehydrate enough if they wait until they’re thirsty. This appears to be potentially dangerous advice.

    Also, I can’t help but feel the risk of hyponatraemia is much lower than the risk of dehydration. Hell, we have people die of dehydration in their homes during hot summers, and on the whole most people don’t appear to drink enough water during their daily life. Are we sure we can trust people to drink enough water if we start telling them to drink less and that they risk dying from drinking too much? If this became mainstream, I think you’d see dehydration rates far surpass the 12-20 cases of hyponatraemia in “recent years” (whatever that means – is that 3, 5, 10 or how many years?)

    • Fully with you on that one sam. I do long distance running and endurance multi sport races and what I have been taught from coaches as well as all the information I have read is that you want to be constantly taking on fluid. Not shocking the system with a huge amount but you should be sipping fairly frequently so that you don’t feel thirsty. Only time you would consider not taking on much fluid would be a sub 45min race but if fluid is available then go for it.

  • The initial advice is simply incorrect. Just go to the finish line of any long event race or otherwise, where there has been a prolonged period of exertion, and take blood samples. It should be pretty clear that most participants are dehydrated and electrolyte depleted. So yes, this advice if posted in the public domain is harmful and I dare say would litigation in the case of a death or injury sustained by someone applying this advice.

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