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Baltimore Marathon runners should watch out for hyponatremia

Hydration is an important element of training for a big race, such as this weekend's Baltimore Marathon. Runners and other endurance exercisers don't want to drink too little, but they also don't want to drink too much. That can dilute the salt in your body and cause hyponatremia, according to Dr. Matthew D. Sedgley, a sports medicine doctor for MedStar Health and a team physician for area universities. He answers questions about the condition.

What is hyponatremia and who is at the greatest risk?


As many of us train for the Baltimore Running Festival, we practice running and fueling during the race. We may not think about hydration, but it is a very important part of running a safe race. Interestingly, in the early days of distance running, it was thought that drinking any liquids was unwise as it might upset the stomach. Now we know that drinking when thirsty is the right advice.

Unfortunately, some runners will drink excessive fluids. This coupled with sweating out salt can lead to a condition called exercise-associated hyponatremia, where the salt in our blood is diluted by too much fluid intake.


Hyponatremia can present with symptoms as mild as nausea, muscle cramps, swelling or puffiness in extremities, headaches and lightheadedness. Severe forms can show up as mental confusion or seizures. There are even a few severe cases of hyponatremia resulting in coma or even death.

Sports medicine and emergency room physicians have studied hyponatremia. It is known that certain risk factors make it more likely. If you are a slower runner (over 4-hour finish for marathon), take a medicine called NSAIDs (like ibuprofen), have a lower body weight being female, and if it is extremely hot or cold on race day and/or you drink excessively on the course, you may be at increased risk of developing exercise-associated hyponatremia.

How does high-intensity exercise cause the problem?

Distance running can place stress on the body. As you run, the best advice to prevent exercise-associated hyponatremia is to only drink when thirsty. Interestingly, this condition can occur even when drinking sports drinks, which may have some electrolytes but can still dilute the runner's concentration of salt in their blood.

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How is it treated, and does it require medical attention?

Treatment for exercise-associated hyponatremia is based on the runner's symptoms. In critical situations when runners are confused, having a seizure or at risk for a coma, rapid treatment with IV fluids with concentrated salt is recommended. However, in minor cases, drinking salty bullion broth can be enough to assist in correcting the symptoms. It is sometimes the case that the salt level in the blood can be checked to help determine the magnitude of the problem.

What is the right amount of sports drink and/or water to consume during exercise?

Again, if runners remember one thing it would be to drink only when thirsty. It's a simple way to avoid this common running-related problem.


Is there lasting harm from the condition?

If recognized and treated promptly, almost all cases of exercise-associated hyponatremia resolve. Only very rarely is there lasting neurologic damage, and this is seen in severe cases.