Editor’s Note: Last week, we ran a column by Dr. Gabe Mirkin titled “The One Mineral to Replace During Exercise.” It detailed the need to replace sodium but no other mineral when exercising. Reader Michael G., who is a physician assistant, wrote a follow-up question regarding the article:
It's a pleasure to read RBR and think about how articles may apply to me and my friends who ride. Another interesting nutritional matter is electrolyte levels and which ones do and don't need replenishment. Dr. Mirkin states we only need be concerned with sodium losses and replenishment. I wish he would comment on potassium balance. His article does not mention it at all.
Well, one quick email to Dr. Mirkin, and following is his response. Our thanks to Gabe for being so willing to contribute his expertise.
By Gabe Mirkin, MD
Sports drink promoters have convinced many athletes that they need special drinks to replace potassium during exercise. When body levels of potassium are low, the kidneys and sweat glands conserve potassium so effectively that potassium deficiency rarely occurs in athletes (International Journal of Sports Medicine, June 2009).
Tiredness in healthy athletes can have many causes, but low potassium is not one of them (Women and Exercise. Ed. by Shangold and Mirkin.pub. by F.A.Davis, Phila. 1987. A referenced medical textbook for physicians. Chapter on Eating for Competing by Mirkin, G.B.).
In 1967, Dave Costill brought some of America’s best marathon runners to Ball State University and could not drop their potassium levels by feeding them a low-potassium diet consisting primarily of hard candy. Potassium is the major mineral inside all animal and plant cells.
So all fruits, vegetables, meat, chicken, fish and almost everything else are rich sources of potassium. Even with prolonged exercise in very hot weather, potassium needs can be met by eating virtually any food.
Potassium deficiency CAN be caused by certain drugs, such as diuretics or corticosteroids, or by severe diarrhea or repeated vomiting.
Several years ago, one of the best female long-distance runners in the country came to me to find a cause for her sudden drop in performance. All tests I ordered were normal except for low blood levels of potassium. I knew that hard exercise does not cause potassium deficiency and that the most common cause of potassium deficiency is vomiting (International Journal of Eating Disorders. Jan, 1997;21(1):95-98), but she repeatedly denied doing this.
I then requested that she collect her urine for one day, and the laboratory reported that it contained three times as much potassium as normal. This proved that she was bulemic. To control her weight, she was sticking her finger down her throat to make herself throw up. After she was able to accept the diagnosis, she got help, stopped vomiting and went on to win several national long distance running titles.
With vomiting, you throw up the stomach’s acid (hydrogen) and the blood becomes alkaline. This causes the kidneys to retain hydrogen and consequently lose huge amounts of potassium in the urine. In both athletes and non-athletes, the most common cause of low potassium blood levels and high potassium urine levels is vomiting.
Gabe Mirkin, M.D., is a sports medicine doctor and fitness guru. A practicing physician for more than 50 years and a radio talk show host for 25 years, Dr. Mirkin has run more than 40 marathons and is now a serious tandem bike rider with his wife, Diana, often doing 30-60 miles in an outing. His website is http://drmirkin.com/.