With the arrival of warm summer days, many of us are hitting the roads and trails to train for and participate in endurance events. Hot temperatures + exercise = sweat, and the need to hydrate to maintain performance becomes increasingly important. Gone, however, are the days of worrying only about drinking enough; we now know that athletes must be aware of the risks of overhydration. When it comes to exercise, excessive drinking can be a dangerous thing.
Case in point: Cynthia Lucero and the 2002 Boston Marathon. With finish temperatures forecast in the 70’s—hot for marathoning–Cynthia made sure to hydrate before the race. She consumed large quantities of Gatorade during the first twenty miles and looked strong at the base of Heartbreak Hill before passing out near Cleveland Circle. Transported to a hospital in a coma, Cynthia Lucero died on April 18, 2002 at the age of 28. Doctors determined the cause of death was swelling of her brain, brought on by excessive hydration.
Excessive hydration can lead to a condition called hyponatremia. This occurs when water intake is sufficient to dilute the normal concentration of sodium in extra-cellular fluid within the body. Research with endurance athletes during intense exercise has also demonstrated inappropriate secretion of arginine vasopressin, the body’s main antidiuretic hormone. This combination of dysfunctional hormone release with excessive, voluntary fluid intake can lead to the development of hyponatremia. Early signs of hyponatremia are nausea, vomiting and headache. Later signs include confusion, disorientation, seizures and coma. The most severe effects are pulmonary and cerebral edema, or swelling of the lungs and brain, both potentially fatal conditions.
Although death from hyponatremia is relatively rare, exercise-associated hyponatremia (EAH) has recently emerged as the most common life-threatening complication in endurance sports participants.” To make matters even more worrisome, there is no easy, one-size-fits-all solution for the problem of how much to drink. Each athlete is different, and current research recommends that every athlete develop an individual hydration strategy optimized to their own physiology and activity. Factors to consider include sweat rate and electrolyte losses (which in turn are influenced by, among others, body weight, genetics and metabolism); temperature; humidity; clothing; and the type of activity.
Here are some general guidelines to keep in mind:
• Start your workout at normal body water and electrolyte levels. Consuming food or beverages containing sodium may be helpful in stimulating thirst and helping your body retain fluids.
• Any fluid intake in excess of the amount that the body can naturally excrete through sweat and urine, about 800 to 1000 mL per hour, places you at risk of hyponatremia.
• Beverages containing electrolytes and carbohydrates may be more effective than water alone.
• The consensus recommendation is to drink ad libidum during exercise. In other words, drink when you’re thirsty.
For more tips on managing your fluid intake check out this article at Runners World.
Finally, dehydration is still the more common foe, so do make sure to hydrate adequately during exercise. Get outside and have fun, but remember: Hydration in moderation.
For more tips on safe training for running check out CPMC Running Clinic at the Sports Wellness Center. More articles related to training for running and running injuries can be found on the running tab.
1. Boston Globe
2. Rogers, IR, Hew-Butler, T. 2009. “Exercise-Associated Hyponatremia: Overzealous Fluid Consumption.” Wilderness and Environmental Medicine, 20: 139-143.
3. ACSM press release of February 8, 2007. “Exercise and fluid replacement position stand now available: American College of Sports Medicine releases new, revised hydration recommendations.” Accessed June 17, 2011 at ASCM.com.
4. Rogers and Hew-Butler (2009).
5. ACSM press release (2007).