It may seem ridiculous to worry about dehydration while skiing. Though surrounded by water (snow), skiers risk dehydration from a variety of factors. First, people tend to drink less while skiing. Cold diminishes feelings of thirst and raises the hassle factor of drinking: water bottles freeze, fingers get cold, and near frozen drinks are unpleasant to gulp. Despite the cold, bodily water losses can be as great in the winter as in the summer. Winter air has very low absolute humidity, which rapidly evaporates not only sweat but also water from the respiratory tract. Further, many people overdress causing overheating and increased sweat production. Finally, exposure to cold can cause increased urine production known as cold diuresis.
Excess water loss causes dehydration, which can create problems for the cold weather adventurer. When dehydrated, our bodies try to keep reduced blood volume in the core to serve vital organs. This results in vasoconstriction reducing blood flow to fingers and toes, which increases the risk of frostbite. Dehydration also can result in extreme fatigue, confusion, and hypothermia.
Sweat Science
Many athletes are taught to “replace what you lose” during exercise by drinking loads of fluids. This can be a bad idea. Since an exercising body cannot efficiently absorb water and nutrients, trying to match ongoing losses results in overfilling of the stomach leading to bloating, cramping, nausea, vomiting, diarrhea, and poor performance. Exercise science has taught us that a much more effective strategy is to replenish our water and nutritive losses in accordance with our absorptive mechanisms.
A rule of thumb is to feed your body back about a third of its ongoing water and nutrient losses during exercise. For the average size person that would be roughly 16 – 20 ounces per hour. That is the maximum rate at which it can be reasonably expected to absorb water and nutrients without harming performance.
Exercise results in “deficit spending” of water and nutrition. These deficits can and should be more properly replenished later during rest mode when our bodies can optimally process food and water. The goal of exercise hydration and fueling is to postpone fatigue and optimize performance by taking in only the fluids and nutrients it can comfortably absorb. It should not be the futile, pseudoscientific effort to constantly replace all ongoing losses of body fluids and nutrients.
Be aware that it is not necessary to hit the nutrition goals precisely. Our bodies have enormous reserves of nutrients and efficient mechanisms for adjusting for variation.
Thirst is a natural instinct that tells us when we are getting dehydrated. Don’t ignore it.
Athletes who start out exercising in a poorly hydrated state are at far higher risk of reaching dangerous levels of dehydration. Pre-event dehydration can occur by poor drinking habits, consumption of drugs like alcohol, caffeine, nicotine, and certain medications like diuretics. A well-hydrated person will have colorless or slightly yellow urine.
Avoid excessive sweat losses by shedding layers as you heat up when exercising. Sweat helps cool you only if it is allowed to evaporate. Saturating your clothes with sweat wastes your precious body fluids and electrolytes. These soaked clothes will fail to insulate when you become chilled later.
Fueling Strategies
Some elite endurance athletes carefully calculate rates of water, energy, and electrolyte losses and attempt to replace them at optimum rates of in-race supplementation using various pills, goos, and energy drinks. Some authorities (especially those with financial connections to the makers of these products) would have you believe that eating food and drinking water are improper sources of exercise nutrition for racing and hard training. While industrial preparations may be effective, commonly available real foods can provide healthier, cheaper alternatives for most scenarios.
Most authorities agree that adventures of more than two hours duration require refueling with appropriate amounts of liquids, energy (in the form of complex carbohydrates), and moderate amounts of sodium and other electrolytes Highly processed sugars should be avoided.
For sports nutrition geeks who favor liquid fueling, it is reasonable to mix up bottles of commercial powdered mix (such as Perpeteum by Hammer nutrition) for drinks that supply all exercise energy, water, and electrolyte needs. These are designed to provide good sustenance when mixed with 20 ounces of water and consumed over each hour of exertion. Another, possibly more satisfying, and certainly cheaper approach is to simply pack food and water as most of us do already. One-half a good old peanut butter and jelly sandwich paired with a bottle of water works well, as does an apple and some almonds:
|
Perpeteum, (2 scoops) |
1/2 PB&J sandwich |
Apple + 1/2 oz. almonds |
|
|
Calories |
180 |
216 |
180 |
|
Carbs (g) |
36 |
30 |
27 |
|
Protein (g) |
5 |
6 |
4 |
|
Fat (g) |
2 |
9 |
8 |
|
Sodium (g) |
147 |
250 |
52 |
|
Potassium(mg) |
80 |
118 |
286 |
|
Calcium (mg) |
24 |
8 |
50 |
|
Magnesium (mg) |
5 |
34 |
50 |
These examples provide reasonable amounts of electrolytes, complex carbohydrates, and protein that are thought to aid in prolonged endurance performance.
Exertion Dilution
Over-zealous hydration during exercise can lower blood sodium levels via a dilutional effect. This potentially dangerous medical condition is called exertional hyponatremia (EH). It generally requires exercise times in excess of 3-4 hours coupled with inadequate intake of food or electrolyte-containing sports drinks. Early symptoms include nausea, vomiting, and headache. Later signs include confusion, disorientation, seizures, coma, and fluid in the lungs. Women are at higher risk for the development of EH than men. Other risk factors include low body weight and the use of nonsteroidal anti-inflammatory drugs (Motrin, ibuprofen, Aleve, naproxen, etc.) Do not attempt to prevent this condition by loading up on salt (sodium chloride) before endurance exercise. For a variety of complex physiological reasons, this doesn’t work. Simply speaking, a high sodium diet hones the body’s ability to excrete excess salt making it hard to cope with the dehydration and sodium losses of exercise. Also, a high sodium diet can cause a host of health problems.
Winter Hydration Tips:
- Pre-hydrate
Two to three hours before an athletic event, consume approximately 20 ounces of fluids with some food. Then follow this up by drinking 10 ounces ten minutes prior to exercise. - Drink early, drink often
Don’t wait to drink. Studies show that people are already about 2 percent dehydrated by they time they feel extreme thirst. Drink moderate amounts fairly often. - But not too much
Limit yourself to 16- 20 ounces per hour. Drink when thirsty but don’t force-feed fluids – moderation is the key. - A general rule of thumb
Your urine should be ample and light yellow or clear. - More than just water
Water is best absorbed when accompanied by electrolytes and complex carbohydrates. This can be effectively done with ordinary food and water or with sports drinks. - Conserve water
Shed layers when you warm up to avoid excessive sweating and, thus, prevent fluid losses. - Prevent frozen liquids
Place a water bottle in an insulated case such as the Water Bottle Parka made by Outdoor Research. Then place this in the center of your pack. - Drink warm liquids
A nice trick is to fill a stainless steel vacuum thermos with hot tea providing a warming treat on the trail
This article was originally printed in the Catamount Trail Newsletter and was authored by Dr. George Terwilliger, an ER physician who lives in Brattleboro and is a lifelong Vermont resident. He is an avid backcountry skier and has skied many sections of the Catamount Trail.
