Cold Sweat: Winter Dehydration
How winter conspires to dehydrate youby Chris Solomon
In 1997 Charlie Fowler and his partners had just been rebuffed in their bid for a first ascent of the north face of western Tibet's 25,242-foot Gurla Mandhata. Descending toward base camp the rope team fell and slid 1,500 feet. Fowler's left leg was badly torqued, the team's stove smashed and scattered. No stove meant no water. A several-hour descent became a parched, three-day ordeal for Fowler. Frostbite claimed parts of five toes, even in relatively mild (by Himalayan standards) weather. "My big toe on my right foot, it's pretty much all gone," Fowler says—and he blames intense dehydration for making his extremities so vulnerable.
Think you don't sweat much in winter? Think again.
There's a lesson here for Average Joes who like to play in winter. While in summer dehydration approaches as obviously as the sweat on your brow, in winter unseen factors conspire to dehydrate you, the cold-weather athlete, and can undermine your performance and safety.
Simply step out of the car on a powder day and the assault begins. Moisture is plucked from your mouth, throat and lungs with every breath, as the body humidifies winter's dry air so the lungs can use it, says University of Connecticut professor Lawrence Armstrong, author of "Performing in Extreme Environments."
Next, the body's exposure to cold weather triggers a process called cold-induced diuresis, which raises blood pressure and makes the kidneys work harder, so they produce excessive urine, says Robert Robergs, director of the exercise physiology laboratories at the University of New Mexico. Sudden increases in elevation, like flying to Vail from Seattle to ski, also trip a complex response that results in more urine production, says Robergs.
Perhaps most insidiously, snowshoers and skiers who are wrapped in layers often have no idea just how much they're sweating. A normally-attired skier exercising moderately to heavily at 32 degrees can lose 4 pounds of sweat in just one hour, researchers have estimated, or 2 percent of a 200-pound male's weight. Only a 1 to 2 percent loss begins to spur bodily responses such as increased heart rate. Perspiring pulls liquid from the bloodstream, and if unreplaced, the blood volume drops and the heart must pump harder to keep that diminished amount circulating. Neurotransmitters send the brain a message: You're pooped. Muscle control erodes, which increases the possibility of accidents, says Robergs.
Finally, dehydration spurs vaso-constriction, in which the body summons its reduced blood volume back into your core, to serve the vital organs. Your digits, now less warmed by blood, become more vulnerable to frostbite, says Dr. Peter Hackett, president of the International Society for Mountain Medicine.
As for Fowler, "Since my frostbite accident I've gone higher and colder in the mountains" without incident, he says. But he adds, "I'm drinking well."
Winter hydration tips:
- Start right. Slowly drink about 17 oz. of water more than one hour before you exercise.
- Drink early. Studies show that people are already about 2 percent dehydrated by they time they feel thirsty.
- Drink often. It's not rare for a hard-charging skier to perspire one quart of fluid an hour, or more. Drink 6 to 10 oz. every 15 minutes. A general rule of thumb: Your urine should be no darker than lemonade, and ample.
- Gatorade or Water? Sports drinks may help the gut absorb fluid a modest amount faster than water alone, but water is a perfectly fine hydrator, says Dr. John Castellani, research physiologist at the U.S. Army Research Institute of Environmental Medicine's Thermal and Mountain Medicine Division. (Carry an energy bar for carbs, though.)
- Don't stop when the lifts stop. Alcohol dessicates an already-dehydrated body. Replace sweat with water before you hit the bar or hot tub.