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Don’t drink too much or too little when running

Take on water before you feel thirsty. Aim for at least eight glasses of water daily. Sounds like good advice—and you’ve certainly heard those refrains before. But these statements fall short on the truth. And unfortunately, this advice has led to many athletes drinking too much water during exercise—a dangerous practice that can lead to serious health complications.

Last February, a panel of 17 top international experts in sports medicine, exercise physiology, and athletic training held a conference to discuss the issue of fluid imbalance—and how it can be prevented during exercise. When you drink too much water before, during, or after exercise, your blood sodium concentration falls below normal. This overwhelms your kidneys, which can’t remove the excess water. Cells start to absorb the water, leading to swelling in the body and a condition known as Exercise-Associated Hyponatremia (EAH). The symptoms of EAH can be mild (dizziness, nausea) to more dangerous (headache, vomiting, confusion, seizure) and can be life threatening.

Cases of EAH are most often reported during military training exercises, marathons, triathlons, and ultramarathons. The biggest risk factor for EAH is consuming too much fluid (water or sports drinks) for a sustained period in relation to your sweat and urine loss. People who are at greater risk for EAH include those with a smaller build, slower runners, and those drinking more than they are sweating. Athletes competing in long events, like ultramarathons or Ironman triathlons, in hot or humid conditions are also at greater risk. That’s because these athletes sweat for prolonged periods of time, which can make it difficult to replenish sodium with sufficient food or beverages mid-competition.

The most important thing you can do to be safe when exercising is to listen to your body. If you are exercising and start feeling unwell (dizzy and nauseous), stop and seek medical help immediately. When you are thirsty, drink water. Thirst is a good way to avoid dehydration and prevent overconsumption of fluids. The only time you should drink before feeling thirsty is if you are participating in an event where you anticipate excessive and rapid sweat losses. And in those instances, you should work on developing a plan for fluid and electrolyte replacement for during and after the event. All runners can stay properly (and safely) hydrated by following these simple tips:

  • Have a water bottle on-hand and take sips when you feel thirsty.

  • If you are participating in an endurance event (longer than an hour or two), alternate between a sip of water and sports drink at aid stations.

  • Prior to an endurance event, don’t restrict your intake of sodium-containing foods.

  • After a sweaty run (and particularly if you can see white salt streaks on your clothes), don’t hold back on salting your food. In these instances table salt is an important source of sodium.

Adapted from a recent Runner’s World article.

Peter Davis MBE

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