Surprised and even a little frightened last April by The New England Journal of Medicine. Five days before the Boston Marathon, the NEJM published a major article showing that 13 percent of runners in the 2002 Boston Marathon might have suffered from hyponatremia, a dangerous condition caused by drinking too much fluid. The figure was surprising because Boston draws the best, fittest, and most experienced runners in the world. If Boston has a 13-percent rate of hyponatremia, what is it at other marathons? Frightening because four runners, all women, have died of exercise-associated hyponatremia in the last 12 years after participating in marathons.
This form of hyponatremia, or low sodium, is caused when overhydration while exercising dilutes the sodium level in your body. Possible result, in the most serious cases: Brain swelling that could lead to seizures and other life-threatening complications. This makes hyponatremia arguably the most important marathon-related health risk facing you and your buddies.
The history of exercise-associated hyponatremia revolves closely around Tim Noakes, M.D., the noted South African sports-medicine physician and author of the encyclopedic The Lore of Running. In the 1970s, Dr. Noakes was a devoted marathoner who ultimately completed the 54-mile Comrades Marathon seven times. At the time, he wrote three articles encouraging his fellow runners to drink more fluids.
But a strange thing happened in the early 1980s. Dr. Noakes started getting calls from athletes and emergency-room doctors faced with a condition never seen before at road races: overhydration. The runners actually seemed to have consumed too much fluid. In 1985, Dr. Noakes published the seminal paper in the field, "Water Intoxication: A Possible Complication During Endurance Exercise." In it he wrote that the condition appears to be caused "by voluntary hyperhydration." If anyone read the paper beyond Dr. Noakes' immediate family, there was little indication of it.
But runners and Ironman triathletes kept developing hyponatremia, Noakes and colleagues continued to publish more papers, and other researchers grew interested in the field. By the mid 1990s, a New Zealand physician named Dale Speedy, M.D., was conducting detailed hyponatremia studies at the Ironman Triathlon in Auckland. In one of his most thorough studies, Dr. Speedy found that 18 percent of the Ironman finishers were hyponatremic. In the last five years, hyponatremia studies have been published by American researchers at the San Diego Rock 'N' Roll Marathon, the Houston Marathon, and the Pittsburgh Marathon, as well as Boston.
By late 2001, Dr. Noakes was invited to write an "Advisory Statement on Fluid Replacement During Marathon Running" for the International Marathon Medical Directors Association. In the paper, he recommended that marathoners drink 400 to 800 milliliters/hour (13.5 to 27 fluid ounces). Dr. Noakes's advice touched off a firestorm, as it was basically 50 percent lower than the widely quoted recommendations of the American College of Sports Medicine, the National Association of Athletic Trainers, and other sports medicine groups, which have generally advised endurance athletes to drink 600 to 1200 ml/hour (20 to 40 ounces). This is more or less where things stood before the NEJM publication last spring.
Hyponatremic in Boston: º¸½ºÅÏ¿¡¼ Àú³ªÆ®·ýÇ÷Áõ
After the NEJM article appeared on April 14, I waited a month before contacting the main author, Christopher Almond, M.D. I figured he was probably burned out from the media uproar, but it turned out he was eager to talk. "The running population is the most important one for us to reach," he told me.
Dr. Almond's study was large and meticulous, making it probably the best yet in the field of exercise-associated hyponatremia. He and his colleagues obtained prerace and postrace body weights and blood sodium levels from 488 Boston finishers, 63 of whom were clinically hyponatremic after the race. The researchers also performed a sophisticated "multivariate analysis" to identify what actually caused hyponatremia among the afflicted runners, identifying three primary triggers: 1) weight gain during the marathon from excessive fluid consumption; 2) a finishing time slower than four hours; and 3) very small or very large body size.
Of these, the first was the most important. "The strongest single predictor of hyponatremia was considerable weight gain during the race," the study concluded. Another significant finding: A sports drink doesn't protect you from hyponatremia. "In our subjects, we didn't find that consuming sports drinks was any different than consuming water," Dr. Almond said. "Sports drinks are mostly water themselves, and contain only small amounts of sodium."
I asked Dr. Almond if he was surprised that his results didn't identify female gender as a risk factor for hyponatremia, as other studies have found. "I don't think that gender per se is an issue," he said. "On the other hand, a lot of women are small and might run over four hours, and those are definite risk factors."
Our conversation concluded with Dr. Almond returning to a point he had made several times already. "I don't want runners to stop drinking fluids during their marathons," he said. "They should simply aim for a safe middle-ground in their hydration strategies."
Talk About Consumption: ¼·Ãë¿¡ ´ëÇÑ À̾߱â
Coming just six weeks after the NEJM article, this year's annual meeting of the American College of Sports Medicine in Nashville produced a number of lectures, presentations, and discussions on hyponatremia. The big one was the president's lecture on "Exercise Associated Hyponatremia," by Joe Verbalis, M.D.
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Dr. Verbalis, a one-time marathon finisher, is an endocrinologist at Georgetown University Medical Center, where Hilary Bellamy died from hyponatremia after the 2002 Marine Corps Marathon. In his 50-minute lecture, Dr. Verbalis hammered home the point that hyponatremia is caused by two concurrent events: overdrinking; and an "inappropriate hormone response" that limits normal urination. This inappropriate response may be genetic, and can be exacerbated by medications including NSAIDs, which many marathoners take to relieve pain and inflammation. But it is also triggered by stress and, especially, nausea--like the nausea marathoners often feel when there's too much fluid sloshing around in their stomach.
Two hours later, Bob Murray delivered an 80-minute lecture on the "History of Sports Drinks." It's hard for me to imagine that anyone knows more about sports drinks than Murray, a Ph.D. in exercise physiology, a Hawaii Ironman finisher, and the longtime director of the Gatorade Sports Science Institute. Murray acknowledges that neither Gatorade's new Endurance Formula nor the traditional Thirst Quencher will prevent hyponatremia if a runner consumes too much sports drink during a marathon. "We can't add more sodium because the research clearly shows that too much sodium actually impedes hydration," he says. "But we do believe that Gatorade can blunt the rate of decline of plasma sodium concentration." In other words, it might offer protection against an even-more-serious hyponatremia, at least when compared with consumption of water alone.
At the end of his talk, Murray is asked an always vexatious question: If dehydration is so damn bad for you, why are the marathon winners often the most dehydrated runners on the course? "I can only say that I believe they'd perform even better with more fluids," he answers. "Our advice remains unchanged: Drink to minimize weight loss, but don't overdrink. And favor a good sports drink over water."
The Bushman and the Antelope: ºÎ½Ã¸Ç°ú ¿µ¾ç
The next evening I have dinner with Dr. Noakes, who faults various health and sports medicine groups for failing to educate athletes about hyponatremia. "The groups put out the message that thirst isn't a good indicator of hydration status," he notes. "Everyone seems to know that. But how many people understand that it's dangerous to override their thirst and drink too much?"
Dr. Noakes acknowledges that sports drinks are excellent and effective products. They do what they're intended to do: taste good, enter the bloodstream rapidly, and provide water, energy, and electrolytes. It's the incessant drumroll--drink more, drink more, drink still more--that rankles him.
In Dr. Noakes's view, short-term dehydration isn't an illness or health threat, but a condition of human existence. He reaches under the dinner table for his computer, and then plays a four-minute video clip that he watches with childlike delight. The video shows a bushman pursuing an antelope. The hunt starts at a slow walk-trot while a blazing Equatorial sun beats down on both man and beast. Before long, the bushman's forehead and chest are covered with sweat, but he presses onward. This is slow, hot, arduous stuff--a life or death pursuit. Eventually, the bushman seizes the moment, breaks into a sprint, and buries his spear in the antelope's chest. "It makes no sense to me that we have evolved without the ability to continue exercising while dehydrated," says Dr. Noakes, a grin spreading across his face.
A month later, in July, the Clinical Journal of Sports Medicine published the position paper drafted by the first International Consensus Meeting on Hyponatremia, held last March. The Consensus gives you two hydration options: Drink according to thirst; or follow the USA Track & Field guidelines that recommend weighing yourself before and after a workout to determine your unique sweat rate per hour. From this, you can plan how much to drink every 15 to 20 minutes while running a marathon. (Sixteen ounces of fluid for every pound you lose.)
In the future, the most clued-in experts will no longer tell you to drink XYZ ounces per hour. Instead, they'll say: Drink when you're thirsty; or drink only to the point where you are maintaining your body weight, but not gaining weight.
The Finish Line: µµÂø¼±
As marathoners, we're all exercise scientists to one degree or another. We put a lot of time into our training, but also understand that we need to eat and drink optimally to perform our best. Here's what I'm telling my friends this fall:
Weigh yourself before the marathon, and write your weight on the back of your race number. If you need help at the finish line, the marathon medical staff will find this prerace weight very helpful when they attend to you.
During the marathon, drink when you're thirsty, understanding that water, sugars, and electrolytes will help you feel and perform your best. But don't force yourself to drink.
Be particularly careful if you expect to run over four hours, and if you have an unusually small or large body size. Drink less if you begin to get a queasy, sloshy feeling in your stomach.
Don't chug fluids immediately after the marathon. This is a time, according to a 2003 London Marathon report, when the risk of hyponatremia can be quite high, as stomach fluids are absorbed into the bloodstream. Nibble on solid foods and sip a variety of drinks slowly until you feel well recovered.
Happily the word is getting out. After the 2002 hyponatremia deaths at Boston and Marine Corps, the 2003 Boston Marathon had only a six-percent incidence of hyponatremia, and race physicians have told me this figure continues to come down. The London Marathon docs say that "after an educational campaign warning runners of the dangers of excessive drinking," there was only one hyponatremia case at the 2004 London Marathon versus 14 the year before.