Water intoxication--not a runner's high.

If you run for a very long time--racing or training--water may not be your best choice for avoiding dehydration, especially in hot weather. Drinking water without electrolytes can lead to dilution of normal blood sodium concentration. Without the proper amount of sodium, as the blood system absorbs extra water, excess fluid can build up in the brain and lungs. The condition is hyponatremia and the consequences can be fatal (see Running & FitNews, September, 1999). Known fondly as "water intoxication," runners can develop brain swelling and serious amounts of fluid accumulation in the lungs. When this happens, oxygen is not transported into the bloodstream efficiently, and you can become short of breath, nauseated, and disoriented. The problem is more common in female runners.

Researchers from Baylor College of Medicine in Houston studied the development and treatment of marathon and ultradistance runners with pulmonary edema (essentially dry land drowning as the lungs fill with fluid). Seven fit and previously healthy marathoners, ranging in age from 29 to 46, became ill with respiratory distress, coughing pink frothy sputum, low oxygen levels, low serum sodium, and brain swelling. Five were female. The runners received treatment with intravenous fluids containing large amounts of sodium. One woman died. Four additional female runners who competed in the Houston Marathon this year also had the syndrome.

Running shorter distances (an hour or less) does not pose the same risks and water is fine for rehydration. But ultradistance and marathon running in which exertion exceeds four hours can set the stage for hyponatremia. Sweating causes a loss of water and sodium, which reduces the total blood volume. When you drink water it further dilutes the blood. As you begin to feel sick, your natural response may be to drink more water, which can cause your sodium level to become extremely low.

As hyponatremia develops, the symptoms are easy to confuse with other conditions like heart attack or ironically, dehydration or heat stroke. The cruelest irony of all is that the response to these conditions may be to give more water. Making this misdiagnosis, and giving low sodium fluids, can be a fatal mistake. The lesson for each runner--if you are running an hour or more, replace fluids with a sports drink that includes electrolytes. If your exertion lasts longer than four hours, you need to increase your intake of salt beyond that found in most sport drinks. Although your body needs water in order to avoid dehydration, if your exertion is prolonged, water must be balanced with sodium. (Annals of Internal Medicine, 2000, Vol. 132, No. 9, pp. 711-714)

RELATED ARTICLE: SALT SMARTS

* Don't drink more water than you sweat--compulsive water drinkers can start a race with a low sodium level.

* When sweating a lot, choose sport drinks (that contain some sodium) over water (which has none).

* Don't overhydrate in the days before the race. You can't stock up on fluids like a camel.

* Eat a relatively salty diet in the days before the race.

* Eat some pretzels in the last half of the race.

("Running FitNews" Editorial Board Member, Randy Eichner, M.D., Oklahoma City, OK)