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Stay hydrated in the winter months

Most people associate dehydration with hot weather, but you can get dehydrated in cold weather too. It isn’t always easy to get the fluids you need, especially when you’re on a mission. If you’re active outside for less than 2 hours, your risk for getting dehydrated is probably pretty low. But if you’re out in the cold for hours or even days, the combination of heavy clothing and high-intensity activity that makes you sweat could lead to dehydration.

Dehydration happens in cold weather for a number of reasons. Cold weather tends to move blood and other body fluids from your arms and legs to your core, increasing your urine output. Cold weather also decreases your body’s thirst sensation, which is normally an early sign of mild dehydration. Other signs of dehydration include headache, dry mouth, fatigue, muscle cramps, constipation, dry skin, and feeling dizzy or light-headed.

One way to see how hydrated you are is to check the color and amount of your urine. (Snow makes a good test spot.) Dark urine in smaller amounts than usual indicates dehydration. Ideally, your urine should be light yellow.

Are you hydrated? Take the urine color test: Hydrated shows color from Optimal as very pale yellow to Well Hydrated as medium yellow. Dehydrated shows dark yellow colors. You need to drink more water. Brown color: Seek medical aid. May indicate blood in urine or kidney disease. Some vitamins and supplements might cause a darkening of the urine unrelated to dehydration. Adapted from USAPHC by the Human Performance Research Center. hprc-online.org

Water and sports drinks are the best fluids to help you stay hydrated, even in cold weather. Energy drinks can have diuretic effects, dehydrating your body, so avoid using them as a substitute for water or sports drinks. Also avoid drinking alcohol in cold weather. It might make you feel warm initially, but it can reduce your body’s ability to retain heat.

When you exercise in the cold, don’t rely on thirst to tell you when you need to drink. Drink often and before you’re thirsty. You should take in 3–6 quarts of fluid per day (including what’s in your food) during cold-weather training and operations. Make sure to take in enough electrolytes (minerals in your blood such as sodium and potassium) if you’ll be out for more than 2 hours. Drinking too much plain water can cause hyponatremia (low sodium levels in your blood), which can result in severe brain damage or death.

Resources

Hawkins, M. N., Raven, P. B., Snell, P. G., Stray-Gundersen, J., & Levine, B. D. (2007). Maximal oxygen uptake as a parametric measure of cardiorespiratory capacity. Medicine & Science in Sports & Exercise, 39(1), 103–107. doi:10.1249/01.mss.0000241641.75101.64

Higgins, J. P., Tuttle, T. D., & Higgins, C. L. (2010). Energy beverages: Content and safety. Mayo Clinic Proceedings, 85(11), 1033–1041. doi:10.4065/mcp.2010.0381

Kavouras, S. A. (2002). Assessing hydration status. Current Opinion in Clinical Nutrition and Metabolic Care, 5(5), 519–524. doi:10.1097/00075197-200209000-00010

Kenefick, R. W., Hazzard, M. P., Mahood, N. V., & Castellani, J. W. (2004). Thirst sensations and AVP responses at rest and during exercise-cold exposure. Medicine & Science in Sports & Exercise, 36(9), 1528–1534. doi:10.1249/01.mss.0000139901.63911.75

Riesenhuber, A., Boehm, M., Posch, M., & Aufricht, C. (2006). Diuretic potential of energy drinks. Amino Acids, 31(1), 81–83. doi:10.1007/s00726-006-0363-5

Colorado is a popular place for winter sports such as skiing, snowboarding, ice skating, and sledding. According to dripdrop.com, the body’s thirst response is diminished in cold weather (by up to 40 percent even when dehydrated). This happens because our blood vessels constrict when we’re cold to prevent blood from flowing freely to the extremities. (If you’ve ever had cold hands in winter, you know the feeling.) This enables the body to conserve heat by drawing more blood to its core.

But because of this, the body is fooled into thinking it’s properly hydrated, e.g. you don’t feel as thirsty  and your body doesn’t conserve water. Thus, in cold weather, athletes are less likely to drink water voluntarily, and additionally, their kidneys aren’t signaled by hormones to conserve water and urine production increases, a condition call cold-induced urine diuresis.

So diminished thirst response and increased urine production are two contributing factors. Yet, there are several others that can lead to winter dehydration, including:

• Wearing extra clothing. Heavy jackets, long underwear and other pieces of warm clothing help your body conserve heat. But the added weight is one factor that makes the body work between 10 and 40 percent harder. By working harder, the body produces more sweat, contributing to fluid loss.
• Increased respiratory fluid loss. In cold weather, we lose more fluids through respiratory water loss. For example, when you can see your own breath, that’s actually water vapor that your body is losing. The colder the temperature and the more intense the exercise, the more vapor you lose when you breathe.
• Sweat evaporates more quickly in cold air. We often think we aren’t sweating in cold, dry weather, because it tends to evaporate so quickly. This is another factor that can contribute to a diminished thirst response.

So whether you’re hitting the slopes or spending an afternoon cross-country skiing – don’t forget to hydrate!

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