Expert guidelines recommend runners drink only when thirsty. But the Loyola survey found that 36.5 percent of runners drink according to a preset schedule or to maintain a certain body weight and 8.9 percent drink as much as possible.
Nearly one-third of runners (29.6 percent) incorrectly believe they need to ingest extra salt while running. And more than half (57.6 percent) say they drink sports drinks because the drinks have electrolytes that prevent low blood sodium. In fact, the main cause of low sodium in runners is drinking too much water or sports drinks.
“Many athletes hold unscientific views regarding the benefits of different hydration practices,” researchers concluded. The study was published in the June 2011 issue of the British Journal of Sports Medicine.
Drinking too much fluid while running can cause a potentially fatal condition called exercise-associated hyponatremia. It occurs when runners drink even when they are not thirsty. Drinking too much during exercise can dilute the sodium content of blood to abnormally low levels.
Drinking only when thirsty will prevent overconsumption of fluids. “It’s the safest known way to hydrate during endurance exercise,” said Loyola sports medicine physician Dr. James Winger, first author of the study.
Symptoms of hyponatremia can include nausea, vomiting, headache, confusion, loss of energy, muscle weakness, spasms or cramps. In extreme cases, the condition can lead to seizures, unconsciousness and coma.
In recent years, there have been 12 documented and 8 suspected runners’ deaths from hyponatremia, said Loyola exercise physiologist Lara Dugas, Ph.D., a co-author of the study.
The International Marathon Medical Directors Association recommends that runners drink only when thirsty.
The Loyola researchers surveyed 197 runners who competed in the 2009 Westchester, Ill., Veterans Day 10K and 5K runs and two other runs on Chicago’s lakefront. The 91 male runners, on average, had been running for 13 years and had run an average of 1.9 10K races and 0.9 marathons. The 106 women, on average, had been running 8.3 years and had run an average of 1.3 10K races and 0.7 marathons.
In the survey, the runners generally said advertising by sports drink manufacturers had little or no influence on their beliefs. But the behaviors of many of the runners indicate otherwise.
During the 1980s and 1990s, sports drinks ads warned about the supposed dangers of dehydration and recommended that runners drink as much as 1.2 liters (five cups) per hour. Sports drink manufacturers generally have stopped promoting overdrinking. But the unscientific beliefs persist that runners should drink as much as they can or according to a preset schedule.
“We have been trained to believe that dehydration is a complication of endurance exercise,” Dugas said. “But, in fact, the normal physiological response to exercise is to lose a small amount of fluid. Runners should expect to lose several pounds during runs, and not be alarmed.”
Winger is an assistant professor in the Department of Family Medicine and Dugas is a research assistant professor in the Department of Preventive Medicine and Epidemiology at Loyola University Chicago Stritch School of Medicine. The third co-author is Jonathan Dugas, Ph.D., director of clinical development at The Vitality Group.
Based in the western suburbs of Chicago, Loyola University Health System is a quaternary care system with a 61-acre main medical center campus, the 36-acre Gottlieb Memorial Hospital campus and 22 primary and specialty care facilities in Cook, Will and DuPage counties. The medical center campus is conveniently located in Maywood, 13 miles west of the Chicago Loop and 8 miles east of Oak Brook, Ill. The heart of the medical center campus, Loyola Hospital, is a 569-licensed-bed facility. It houses a Level 1 Trauma Center, a Burn Center and the Ronald McDonald® Children’s Hospital of Loyola University Medical Center. Also on campus are the Cardinal Bernardin Cancer Center, Loyola Outpatient Center, Center for Heart & Vascular Medicine and Loyola Oral Health Center as well as the LUC Stritch School of Medicine, the LUC Marcella Niehoff School of Nursing and the Loyola Center for Fitness. Loyola’s Gottlieb Memorial Hospital campus in Melrose Park includes the 264-bed community hospital, the Gottlieb Center for Fitness and the Marjorie G. Weinberg Cancer Care Center.