Cooler fall and winter weather is just around the corner. And adults and kids will soon be partaking in their favorite winter sports: skiing, snow-shoeing, and good, old-fashioned sledding. But in addition to remembering to bundle up for the cold weather, hydration is another important consideration in winter.

We don’t often associate cold-weather exercise with dehydration. The body doesn’t get as hot, and sweat evaporates more rapidly in the cold air. Thus, we’re tricked into thinking we aren’t losing fluids as rapidly.

Dehydration is still a risk when playing in the snow, albeit, for different reasons than summer exercise.

What Causes Dehydration During Winter Months?

In cold weather, the body’s thirst response is diminished (by up to 40 percent even when dehydrated)[i]. 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.[ii] By working harder, the body produces more sweat, contributing to fluid loss.
• Increased respiratory fluid loss.[iii] 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 the answer is a clear “Yes.” The dehydration risk remains in cold weather. Whether you’re hitting the slopes or spending an afternoon cross-country skiing – don’t forget to hydrate!