In the sparkling sunshine yesterday, runners at the finish line of the Boston Marathon said they had taken very much to heart the new warnings about drinking too much water during a race. ”I was conscious of not taking huge amounts of water,” said Ian Bloomfield, 52, of England, who pronounced himself ”quite pleased” with his time of 2 hours 45 minutes. ”I was very aware of hyponatremia,” the potentially fatal result of overhydration. Brian Paff, 24, of Chicago said he had had hyponatremia in a college race. ”I passed out from it,” he said. Yesterday, he was careful not to drink too much.
In a dramatic turnabout, sports doctors now say that drinking too much water can be as bad or worse than not drinking enough. This holds for both endurance athletes and weekend warriors, though most people who exercise for just an hour or so don’t really need to worry about either dehydration or overhydration.
In a study published last week in the New England Journal of Medicine, Boston doctors, who have long made Marathon runners their living laboratory, found that hyponatremia (a low concentration of sodium in the blood because of too much water) occurred in 13 percent of participants. Of the 488 marathoners in the 2002 study, three had such low blood sodium that they were at risk of severe brain swelling, which can lead to brain damage, coma and death.It was during the 2002 Boston Marathon that 28-year-old Cynthia Lucerodied of hyponatremia. Worldwide, some researchers believe there may be as many as one death per marathon, though not all are due to hyponatremia. Sports drinks, once thought to be an athlete’s protection against hyponatremia, turn out not to be. Even though they contain some sodium, it’s not enough to make a difference, the study showed.Many endurance athletes, especially smaller, slower runners who take longer to finish and therefore have more time to drink, actually gain weight during marathons, sometimes as much as 8 to 10 pounds, said Dr. Christopher S.D. Almond, lead author of the study and a cardiology fellow at Children’s Hospital. Women are at greater risk because they tend to be smaller and slower and also, perhaps, because they may more diligently adhere to the old belief that it’s wise to drink lots of water.Excessive water drinking among athletes has become such a concern among sports doctors that guidelines are rapidly changing. At major endurance races around the country, including yesterday’s marathon, doctors now do an on-the-spot test for blood sodium levels on collapsed runners to differentiate between hyponatremia and dehydration. Giving fluids to someone with hyponatremia could be fatal.
The Boston Marathon has had these tests at the finish line for several years and this year, for the first time, had them along the course as well. In addition, Marathon officials provided scales along the route and at the finish line, and encouraged runners to write their pre-race weight on their bibs to check for weight gain.”This has been a major paradigm shift in the last few years,” said Dr. Benjamin Levine, coauthor of an editorial in last week’s medical journal and a cardiologist at the Presbyterian Hospital of Dallas. ”It used to be thought that thirst was a poor measure” of impending dehydration and, therefore, that athletes should drink as much as they could before thirst set in. ”That is clearly not correct,” he said.In 2003, USA Track and Field, which governs track-and-field events, began saying that athletes should use thirst as a guide for fluid replacement. The International Olympic Committee Medical Association began recommending caution in fluid consumption last year, just prior to the Athens Games. The International Marathon Medical Directors Association now advises drinking no more than about 12 to 25 ounces of fluid an hour, especially for slower, back-of-the-pack runners.Other guidelines now in the works are likely to follow suit, including some from the American College of Sports Medicine and a consensus statement from experts who met recently in South Africa and will publish their recommendations this summer. This shift in thinking reflects the growing awareness the dangers of excess fluidconsumption.
”Hyponatremia is less common, but more dangerous” than dehydration, said Dr. Peter Moyer, medical director of Boston Fire, Police and Emergency Medical Services.
Dehydration does have clear, adverse effects on performance, which is a major issue for elite athletes, said Michael Sawka, chief of the thermal and mountain medicine division at the US Army Research Institute of Environmental Medicine in Natick.
”But if you’re not doing high-level performance and you’re not losing a lot of water, it’s not important to drink,” he said. ”There are no real adverse health consequences” to dehydration, except low blood pressure, ”susceptibility to heat exhaustion and, if you’re out there long enough, heat stroke.” Like hyponatremia, heat exhaustion does make people feel ill, get nauseous, have muscle cramps and feel dizzy upon standing up quickly; heat stroke includes all that plus mental-status changes, such as confusion about one’s identity and location. But dehydration ”would have to be extreme and prolonged, like being lost in the Sahara for days, to become fatal,” said Dr. William G. Goodman, a kidney specialist at the David Geffen School of Medicineat UCLA. So how can you tell how much fluid you need during exercise? The best approach is to weigh yourself before and after exercise, said Dr. Arthur Siegel, chief of internal medicine at McLean Hospital in Belmont. If you lose, say, 3 percent of your body weight after a workout, ”that represents mild dehydration,” he said. It is enough, though, to be a ”green light” to rehydrate slowly, over eight to 12 hours. If you gain 3 percent of body weight, that’s serious — a red flag or hyponatremia.So, whether you’re a marathoner or a casual athlete, make it a point to weigh yourself before and after workouts. If you do gain weight, don’t drink fluids (salty broth is OK if you have a headache or salt craving) until after you have urinated spontaneously. The point is to let your body get rid of excess water.