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Water Intoxication

For years, doctors have told long-distance hikers, marathon runners and triathletes to drink as much water as possible during exercise and competition. The logic was simple; the fluid would help athletes avoid dehydration. Now the results of new studies show that drinking too much water when exercising can be as dangerous as drinking too little.

The dramatic shift in public awareness happened during the 2002 Boston Marathon when Cynthia Lucero collapsed and died. She was killed by a condition known as external hyponatremia or water intoxication. Here's what happened.

Athletes who engage in extreme sports often deplete the fuel that powers the body's cells. That causes a hormone called arginine vasopressin to be released. One of the functions of that hormone is to tell the kidneys to hold onto fluids. Under normal conditions, athletes simply pee out any excess fluids, but during extreme sports, their kidneys are being suppressed, leading to a buildup of fluids in the body.

The excess water begins to dilute the athlete's blood. As the sodium levels drop in the blood, there isn't a corresponding sodium drop in the cells.

Since our bodies are always striving for a state of equilibrium, they will attempt to force salt out of the cells by flooding them with fluid. That causes the muscles to swell. This isn't a problem for most muscles because they can bulge out.

The problems happen when the cells in the brain swell as the fluid levels increase. The brain is trapped in our skull, and as its cells take on water, the brain grows in size, but it has nowhere to expand. A swelling brain eventually will cause seizures, respiratory failure and finally, death.

When Cynthia Lucero died this way, doctors realized that even runners who drink sodium-filled sports drinks were at risk.

Since then, two sets of guidelines have been established to help determine how much you should drink to avoid problems of over and under-hydration. The first one is a general rule.

Drink 20 ounces of fluid before exercise. Every hour after, you should take in an additional 28 to 40 ounces more.

For a more specific gauge, you should use a scale.

Drink one pint of fluid for every pound of weight you lose during exercise.

To figure out if you're drinking the right amount, weigh yourself before you begin your exercises. When you finish, weigh yourself again. If you gained weight, you're drinking too much and need to cut back on the fluids. If you're more than a pound less, you didn't drink enough and need to take in more next time.

For you endurance athletes, don't forget to take in salt! If your sweat stings your eyes and you get a white crust of sodium on your skin, you may need more sodium than your body can absorb from sports drinks. Consider increasing your sodium intake from foods 3 to 5 days before a race. (Don't do this if you have high blood pressure or your doctor has restricted your sodium intake.)

Below are a series of recommendations to help determine if someone is experiencing hyponatremia and how to treat them.

Signs and Symptoms:

  • Excessive fluid consumption before, during and after exercising. This results in a net weight gain.
  • Headache and/or disorientation.
  • Nausea and/or repetitive vomiting.
  • Swelling, bloating or puffiness in the face, hands and feet.


  • If blood sodium levels cannot be determined onsite, do not rehydrate athlete as it may worsen the condition. Transport the athlete immediately to a medical facility.
  • Diuretics or intravenous solutions may be necessary to deliver sodium into the body. This should only be attempted by emergency medical personnel.

Please remember, water intoxication is a condition that is primarily a concern of extreme or endurance athletes (such as marathon runners or triathletes). People who gain 4.5 pounds or more from fluids during a competition are the most at risk. Runners who are extremely thin and women are at higher risk. Athletes who drink sports drinks, which contain little salt, are just as likely to develop hyponatremia as athletes who only drink water.

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