August 2003

Current Issue
Past Issues
About Us

Public Affairs
Baylor Home

Public Affairs
Baylor College
of Medicine
One Baylor Plaza,
Room 176B
Houston, TX 77030
Telephone:
  (713) 798-4712
Fax
   (713) 798-3692
Email: pa@bcm.tmc.edu

Comments, Suggestions?

Check out From the Laboratories, an online newsletter that focuses on research.

How much is 'too much' of a good thing?

By Kimberlee Barbour

Ever heard the advice that you should drink eight glasses of water each day?

Is it an “old wives tale” or is it backed by evidence?

John Cianca, MD, an associate professor of physical medicine and rehabilitation at Baylor College of Medicine in Houston, says he isn’t certain where the notion originated, but he knows it is not always true. In fact, he said, it is possible for a person to drink too much water.

Marathoners, triathletes and participants in any physical activity that takes place over a long time are at risk of becoming ill from being overhydrated.

Hyponatremia occurs when the concentration of sodium in the blood in the body falls below normal (measured as 135 millimoles per liter). The body is overwhelmed by increasing fluid levels and may malfunction in its attempt to regulate sodium levels.

Hyponatremia develops slowly and often after exercise has concluded. First, runners complain that they “just don’t feel right,” Cianca said. Then they start to get a headache, become irritable and vomit. Breathing becomes difficult. They may complain of respiratory distress or have seizures. If the person is not treated promptly, he or she could go into a coma or die.

If any of these symptoms occur during or after the race, Cianca recommends seeking medical attention immediately.

John Cianca, MD

“Factors that may increase the incidence of hyponatremia are hot weather, stress, pain, too many fluids and long periods of exercise,” Cianca said. “We are even beginning to think that the menstrual cycle has an effect on the incidence of severe hyponatremia in women.

“The most frustrating thing about hyponatremia is that it is completely preventable,” Cianca said. “People need to be educated on exactly what hyponatremia is and ways it can be prevented. Knowing your body and how much water it needs while exercising is necessary while training.”

Every body is different and loses different amounts of fluids during exercise, Cianca said, and this makes it difficult for physicians to set standard fluid replacement guidelines.

Weighing before and after a workout is the first step to learning how much water the runner’s body needs for exercise. Be sure to towel off sweat before reweighing.

For every pound lost, a person should drink 16 ounces of fluid. If weight gain occurs, too much water was taken in and the runner should cut back on fluid intake next time.

The next step is to design a personalized training program, taking into consideration personalized fluid intake, suggests Cianca.

“The problem with hyponatremia is that runners may not even know they have it until after the race when it could become fatal,” Cianca said. “At the Houston Marathon, the medical tent is set up to test runners who do not feel well. Also there are scales along the course at medical stations so runners can check their weight as they are running.

“More and more participants are running for charities and are not in the most favorable condition to run a marathon,” continued Cianca. “Because many of these participants are walkers or running slowly, they have time to grab a couple of cups of water at each drink stand and are out in the heat for longer periods of time. They believe that they are working harder than they actually are and overcompensate in their hydration thereby increasing their chance of hyponatremia.

“Training is so important for marathon participants," Cianca said. "People need to consider their own capabilities and accept them."

To help prevent hyponatremia, Cianca recommends the following:

• Increase your intake of salt when training in hot weather. This can be done by using more table salt or by consuming foods and beverages with a higher sodium content.
  
• Don’t blindly follow training advice given for groups. Be willing to learn your own fluid needs by checking your weight before and after runs and adjusting to fluid intake accordingly.
  

© Copyright 2002 - 2003 Baylor College of Medicine. All Rights Reserved.