Marathon runners consuming large amounts of water to avoid dehydration during their 26-mile run should know that too much of a good thing can lead to illness.
Twenty-one runners out of the 5,082 race finishers of the 2000 Houston Marathon developed hyponatremia, a condition in which the sodium concentration in the blood drops because there is too much water in the bloodstream and an inadequate excretion of water in urine. Fourteen of these runners required hospitalization.
Excessive exercise and drinking large amounts of water can lead to steep falls in blood levels of circulating electrolytes (salts), which are essential for many body processes.
Symptoms of hyponatremia can include fatigue, confusion, dizziness and, in extreme cases, coma.
The investigators found that the longer it took runners to finish the marathon, the more likely they were to experience hyponatremia, especially in slower runners with finish times that exceeded 4 hours and 20 minutes.
Beginner runners are more likely to stop at water stations at each mile along the 26-mile route consuming a cup or two of water because they were told they could get dehydrated running the race. Elite marathon runners on the other hand may consume water only one time during the race.
To strike a healthy balance, researchers suggest that runners should only drink water when they think they need it, or if they are sweating more than usual, for example, on a hot and humid day.
Runners should not consume more than 800 millilitres (about two cups) of water for each hour they are on the course.
In addition, taking nonsteroidal anti-inflammatory pain relievers before or during the race also increases a person's risk for hyponatremia. Runners should only take acetaminophen before or during a race.
Lastly, runners should consume salty food, like pretzels or a salty bagel, as part of their pre-race meal.
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