Do you believe that exercisers need to take potassium, magnesium or any other mineral? The only mineral that you need to take during prolonged exercise is sodium, found in salt.

The definitive studies on minerals and exercise were done during World War II. Dr. James Gamble of Harvard Medical School paid medical students to lie on a raft in his swimming pool, taking various amounts of fluids and salt and having blood drawn to measure salt and mineral levels. He showed that you have to take a lot of salt when you exercise for several hours, particularly in hot weather. For many years after that, every student at Harvard Medical School heard Dr. Gamble give his lectures on minerals and exercise, and today, most serious students still read the Gamble lectures published in 1958 by The Harvard University Press. Now, more than sixty years later, nobody has improved on his research.

After Gamble published his studies, people who worked or exercised in the heat were given salt tablets. Then doctors became concerned because they thought that a person could have his blood pressure raised by taking in too much salt and some people vomited because of the high concentration of salt in their stomachs. So they recommended restricting salt, causing many people to suffer heat stroke and dehydration during hot weather exercise. A low-salt diet does not lower high blood pressure for most people. A high-salt diet causes high blood pressure usually only in people with high blood insulin levels. Eating salty foods and drinks when you exercise for more than two hours is unlikely to raise blood pressure. We don't recommend salt tablets because they can cause nausea and vomiting.

If you don't take salt and fluids during extended exercise in hot weather, you will tire earlier and increase your risk for heat stroke, dehydration and cramps. We eat salted peanuts and drink water at least every 15 minutes when we ride in hot weather. Potassium deficiency doesn't occur in healthy athletes. The only mineral that athletes need to take when they exercise is regular table salt.

Gabe Mirkin, M.D.

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 Sports Medicine and three other specialties.

Dr. Mirkin's daily features on fitness have been heard on CBS Radio News stations since the 1970's. He has written 16 books including The Sportsmedicine Book, the best-selling book on the subject that has been translated into many languages. His latest book is The Healthy Heart Miracle, published by HarperCollins.

Dr. Mirkin is a graduate of Harvard University and Baylor University College of Medicine. A Boston native, Dr. Mirkin did his residency at the Massachusetts General Hospital. He has served as a Teaching Fellow at Johns Hopkins Medical School, Assistant Professor at the University of Maryland, and Associate Clinical Professor in Pediatrics at the Georgetown University School of Medicine. He has run more than forty marathons and is now a serious tandem bicycle rider with his wife, nutritionist Diana Mirkin.