Tiredness and cramps in athletes can have many causes, but lack of potassium in their diets is not one of them. Many years ago, Dave Costill of Ball State University tried to create potassium deficiency in runners. He couldn’t do it because potassium is found in all foods except refined sugar, and his athletes would not stay on a diet that consisted only of hard candy.

The kidneys and sweat glands conserve potassium so well that you don’t lose much. If an athlete develops potassium deficiency, it is usually caused by drugs, such as diuretics or corticosteroids, or by diarrhea or repeated vomiting. Some athletes try to control their weight by making themselves vomit. This is called bulimia, and the person usually denies vomiting. Their physicians can prove that they are vomiting by ordering blood and urine tests. If blood levels of potassium are low and urine levels are high, vomiting is a likely cause. Ask your daughter’s doctor to do a work-up for other causes of chronic tiredness. If none can be found, she may overtraining and should talk to her coach about changing her workouts.

Don't be misled by advertising for sports drinks that you need to replace potassium during exercise and so need their products. The only mineral you need to replace during exercise is salt. Furthermore, if you did need potassium, it is found in virtually all foods. You don't need to buy special drinks.

Dr. Gabe Mirkin has been a radio talk show host for 25 years and practicing physician for more than 40 years; he is board certified in four specialties, including sports medicine. Read or listen to hundreds of his fitness and health reports at http://www.DrMirkin.com

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