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THE PHYSICIAN AND SPORTSMEDICINE - VOL 31 - NO. 7 - JULY 2003


New Hydration Recommendations

Risk of Hyponatremia Plays a Big Role

Concerns about overhydration and hyponatremia among endurance athletes were once discussed only in sports medicine circles. In May, USA Track & Field, the national governing body for track and field and race walking, issued new hydration recommendations1 that urge runners to hydrate based on individual needs, rather than drinking as much as they can tolerate. Since then, the message has trickled down to mainstream medicine and even the lay press.

Hyponatremia is a hot topic among marathon medical experts and military physicians, because the condition is one of several causes of exertion-related collapse. Though experts agree that successful identification and treatment of hyponatremia depends on distinguishing the condition from heat illness and other diagnoses, disagreements flare about what level of hydration is optimal for the health and performance of athletes.

Two recent reports2,3 in the medical literature seem to confirm a trend that marathon medical experts have observed: Hyponatremia has become more common as greater numbers of less competitive athletes participate in endurance events. A postrace blood study2 done on 481 participants who ran the 2002 Boston Marathon found that 13% experienced hyponatremia. Risk factors included female gender, slower finishing times, and excess fluid consumption. An observational, retrospective, case-controlled study3 of medical care at the 2000 Houston Marathon found that 21 runners (0.31% of entrants) presented to the medical area with hyponatremia. Risk factors among participants included slower race times and excess fluid consumption.

What Led to New Recommendations?

Douglas J. Casa, PhD, ATC, assistant professor in the department of kinesiology at the University of Connecticut in Storrs, Connecticut, wrote USA Track & Field's hydration advisory. He says the organization's intent was to acknowledge hyponatremia concerns that were expressed in a hydration advisory issued by the International Marathon Medical Directors Association (IMMDA) in 20024 and to educate athletes about determining their own individualized fluid needs. "Athletes should understand the risks of both hyponatremia and dehydration," Casa says. "This document gets people involved in finding a middle ground between the two."

The IMMDA advisory challenges the conventional wisdom, contained in, for example, the 1996 American College of Sports Medicine hydration recommendations,5 that endurance athletes should drink as much as they can tolerate during exercise. Instead, the IMMDA advisory states that blanket hydration recommendations for athletes are incorrect and unsafe, and that they should drink as needed, but not to exceed 800 mL per hour.

Casa says that some level of dehydration is inevitable in some endurance activities and that USA Track & Field advises participants to at least replace what they are losing during activity. The USA Track & Field advisory teaches athletes how to calculate their individual sweat rates and how to monitor their hydration status with a urine color chart. "The biggest point we want to get across is that athletes have different sweat rates based on environment, exercise intensity, equipment, and body weight," he says.

Practical Considerations

Casa says he worries that the public may misconstrue the hydration recommendations. He points to a recent New York Times headline6 that says "New Advice to Runners: Don't Drink the Water." He's particularly concerned about athletes in other sports getting the wrong information about hydration. "Runners have a longer time to overhydrate. But in soccer or football, dehydration is more common, because activity is more intense and is often performed in the summer," he says.

William O. Roberts, MD, associate professor in the Department of Family Practice and Community Health at the University of Minnesota in St Paul, says hyponatremia is mostly a problem among slower participants in long-distance or duration events and is not usually an issue in sports such as football, as long as players ingest adequate sodium. When patients ask about the new hydration advisories, Roberts, medical director of the Twin Cities Marathon, emphasizes that they should learn how to calculate and replace their sweat losses.

Roberts predicts that marathon groups will educate runners about the new hydration recommendations and that race volunteers will less aggressively push fluids on runners. Hydration stations will likely be fewer. "The Houston Marathon dropped from 30 to 15, and I'm pressing to go back to 12 for the Twin Cities Marathon," he says.

Timothy Noakes, MB ChB, MD, professor of exercise and sport science at the University of Cape Town and the Sports Science Institute of South Africa in Newlands, South Africa, who wrote the IMMDA recommendations and was the first to describe exercise-related hyponatremia along with the role of fluid overload, say he advises his patients to heed their thirst and to employ the same individualized hydration strategies in competition as they do in training. "I think that's where some of the problems have arisen," he notes.

Future Directions, Debate

Though IMMDA and USA Track & Field's hydration recommendations have generally been well received, Roberts says that some in the sports medicine field believe allowing thirst to guide hydration automatically puts athletes behind with fluid replacement—not dangerously, but enough to affect peak performance. "This should make for some heated and healthy debate," Roberts says.

Noakes says confusion still remains about the real dangers of dehydration. He contends that there is no evidence showing that dehydration levels during competition (2% to 8%) impair health or performance. "There is an urgent need to do properly controlled trials of the effects of weight loss (dehydration) during exercise on performance during weight-bearing activities like long-distance running," Noakes says. "Similarly, there is a need to determine what levels of dehydration carry health risks."

More research is also needed to determine the effects of convective cooling on heat balance during exercise, Noakes says, alluding to his belief that earlier lab studies that suggested the need to drink as much as possible did not match environmental conditions that athletes encounter during competition.

Lisa Schnirring
Minneapolis

REFERENCES

  1. Casa DJ: Proper hydration for distance running: identifying individual fluid needs. Available at https://www.usatf.org. Accessed May 22, 2003
  2. Almond CS, Fortescue EB, Shin AY, et al: Risk factors for hyponatremia among runners in the Boston Marathon. Acad Emerg Med 2003;10(5):534-535
  3. Hew TD, Chorley JN, Cianca JC, et al: The incidence, risk factors, and clinical manifestations of hyponatremia in marathon runners. Clin J Sport Med 2003;13(1):41-47
  4. Noakes T: IMMDA-AIMS advisory statement on guidelines for fluid replacement during marathon running. New Studies in Athletics: IAAF Tech Q 2002;17(1):7-11
  5. Convertino VA, Armstrong LE, Coyle EF, et al: American College of Sports Medicine position stand on exercise and fluid replacement. Med Sci Sports Exerc 1996;28(1):i-vii
  6. Kolata G: New advice to runners: don't drink the water. NY Times. May 6, 2003:F5

Field Notes

Researchers Confirm Head Injury, Parkinson's Risk

Because Parkinson's disease and dementia pugilistica resemble each other, head injury experts have long suspected a link between a patient's history of head trauma and Parkinson's disease. Previous studies looking for a link produced conflicting findings; however, Mayo Clinic researchers recently confirmed the association in a study published in the May 20 issue of Neurology.

According to a press release from the Mayo Clinic, researchers reviewed the medical records of 196 patients participating in the Rochester Epidemiology Project. Patients who had Parkinson's disease were age and gender matched to a patient who did not have the disease. Researchers found that severe head injury—longer loss of consciousness with brain bruising visible on computed tomography—was associated with Parkinson's disease. The association did not hold true for mild head injury (no or only brief loss of consciousness). Study results also found an association between head injury severity and Parkinson's disease; those who required hospitalization had the greatest risk.

Researchers said the strength of the study is that it is based on medical records rather than human recall.


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