Fighting record heat, as well as the mile-high altitude, runners in the recent Colorado Colfax Marathon downed water at such a pace the event could have been nicknamed the Big Gulp.
Volunteers set out countless cups of the precious coolant at 16 water stations along the route, helping ensure a successful finish for more than 5,000 entrants in the marathon, half-marathon and relay.
Despite the heat (the temperature reached 91 degrees by mid-afternoon), Dr. Bruce Evans, the medical director, said only about 90 people – “fewer folks than we anticipated” – stopped at the first-aid tents, and not all their ailments involved dehydration.
“I think the runners did a good job of hydrating themselves beforehand and pacing themselves during the race,” he said.
Race director Mike Collins agreed. “Most people in marathons know enough to drink enough,” he said. “And in Denver, they know you need to drink more because of the high altitude (which forces people to breathe more heavily) and how dry it is.”
More, yes. But how much more? And, aside from checking to make sure your urine is clear or pale yellow in color, how do you know when you’re drinking enough?
Those questions become more crucial for athletes of all types at this time of year, as people start exercising more outdoors. But while individual needs vary, the answers appear to be much the same for tennis players, bicyclists and hikers as for long-distance runners.
Under everyday conditions, reports the Institute of Medicine, an arm of the National Academy of Sciences, people are adequately hydrated if they are taking in enough liquid to replace all they lose in urinating, sweating and breathing – an average of 3.7 liters per day for men and 2.7 liters for women.
Given that 20 percent of the total is typically derived from food and 80 percent from beverages, this means men should drink about 3 liters per day and women about 2.2 liters – or roughly the same amount dictated by the old arbitrary 8-by-8 rule – meaning eight 8-ounce glasses per day.
But researchers caution that people must drink more when they’re physically active in hot weather, and much more – even six liters or more – when the exercise is strenuous and prolonged.
Dr. Lawrence J. Appel, a Johns Hopkins epidemiologist who chaired the panel of experts who came up with the base values in 2004, noted at the time that water need not be the only source of fluid replacement.
“While water is a frequent choice for hydration, people also get water from juice, milk, coffee, tea, soda, fruits, vegetables and other foods and beverages, as well,” he stated.
But the panel’s suggestion that people “let thirst be their guide” in determining how much to drink was challenged by the American College of Sports Medicine, which represents some 20,000 physiologists, fitness coaches and other exercise professionals.
Larry Kenney, its president, declared that “thirst alone is not the best indicator of dehydration” – in part because the sensation of thirst can be quenched before the body’s fluid levels are fully replenished.
The Indianapolis-based organization, which is holding its annual convention in Denver later this week, now recommends a two-step hydration regimen for people who engage in intense exercise in hot weather, such as trail runners, mountain bikers or triathletes.
First, the ACSM advises, determine your standard sweat rate by weighing yourself naked before and after an hour-long workout with no fluid intake. Then, figuring that 1 pound of weight loss equals 16 ounces of sweat, arrange to drink enough liquid before, during and after each subsequent session to replace the fluid you lose.
“You don’t want to wait until the day of the event and rely on what your body is telling you, or on whatever you’re handed on the street,” says Celia Sladek, a physiologist at the University of Colorado Health Sciences Center.
Proper hydration, experts point out, is important not just because it keeps the blood and breathing systems running smoothly, but because it optimizes one’s performance – especially in warm weather. In a study published last fall, for example, U.S. Army researchers found that a 3 percent drop in body weight – equal to 4 1/2 pounds of fluid loss for a 150-pound athlete – cut performance by 8 percent, even at a relatively moderate temperature of 68 degrees.
“We measured performance as work performed (in kilojoules), but the real indicator is time,” said Samuel N. Cheuv-
ront, the lead researcher. “Eight percent over the course of a marathon is the difference between finishing in 2 hours 30 minutes or 2 hours 42 minutes – and that’s a big difference.”
Besides staying hydrated, health experts note, active people should take care to replenish their electrolytes – particularly potassium, which Americans typically underconsume.
“You need to replace both water and salt when you exercise, and in that sense sports drinks can probably put you on the right track,” says Alan Kim Johnson, a research physiologist at the University of Iowa.
With too much fluid and not enough salt, he notes, an athlete can fall victim to hyponatremia, or overhydration, a rare but potentially fatal condition characterized by swelling of the brain.
CU’s Sladek, who has done research on the role of certain hormones in regulating behavior, suggests that some cases of overhydration may be traced to an anti-diuretic hormone that causes the kidneys to conserve water.
“Basically, our bodies are set up so we can excrete excess water if we get more than we need,” she says. “But there may be something, perhaps stress, that can improperly trigger the release of this hormone, and that’s one way you could get into trouble.”
Staff writer Jack Cox can be reached at 303-820-1785 or jcox@denverpost.com.
