Training never stops, even in the winter, but extra vigilance is required during cold weather exercise. Though you may not realize it, your body loses a significant amount of water in the cold, especially during exertion. First, winter clothing tends to be bulky and can make the body work up to 40 percent harder than usual, increasing sweat losses. Pair that with an increased metabolic rate (our body’s mechanism for keeping us warm), and your body’s internal temperature will rise signaling evaporative cooling (a.k.a. sweating) to help regulate core body temperature.
Second, sweat evaporates more quickly in cold temperatures, swiftly turning into vapor. Not only does this contribute to dehydration, but because we don’t see sweat drops on our skin, we might miss the visual cue to drink more fluids.
The third thing to consider in cold weather is respiratory water losses. Breathing cold, dry air causes the body to lose significant amounts of water through respiration. When you can see your breath on a cold winter run, what you’re actually seeing is water vapor that your body is losing. The colder the temperature and the more intense the exercise, the more vapor and fluids you’ll lose.
Finally, urine production will increase in cold weather making us assume we’re well-hydrated even if we’re not. The reason: in cold climates, our bodies redistribute blood volume from the extremities to the core to protect our most important organs.
Typically, when we’re dehydrated, our body releases antidiuretic hormone AVP (plasma arginine vasopressin) which signals the body to slow urine production in order to reduce urinary water losses. However, in cold weather, our brain perceives the shift in central blood volume as indicative of adequate hydration and body water levels. So even if you’re dehydrated, the antidiuretic hormone AVP will not increase, resulting in increased urination and further adding to dehydration.
Are you heading to the mountains this winter? If so, take altitude into consideration. At altitude, you’ll be working a lot harder than you would be at sea level to achieve the same levels of blood oxygenation. To cope with the fall in atmospheric pressure at altitude, ventilation (the process of moving air in and out of the lungs) increases to meet the body’s demand for oxygen. Because our breath is saturated with water, the increased breathing rate results in increased water losses, prompting dehydration.
Thirst is not reliable in cold climates. That’s right, cold weather actually suppresses your body’s thirst sensations! In one study, researchers found that cold exposure reduced thirst by up to 40 percent at rest and during moderate-intensity exercise.
This could be due to the fact that our blood vessels constrict in cold temperatures (peripheral vasoconstriction), which then leads to an increase in central blood volume and stimulation of central volume receptors, essentially tricking the body into thinking it’s well-hydrated.
So if you don’t feel thirsty when training, beware. You could be getting dehydrated without realizing it.
TIPS TO AVOID DEHYDRATION IN COLD TEMPERATURES
- Pre-hydrate with an electrolyte beverage like Osmo PreLoad before you exercise
- Sip fluids frequently when exercising outdoors, even if you’re not thirsty
- Drink warm or room-temperature fluids to help keep your internal body temperature regulated
- Wear wicking clothing which will do a better job regulating body temperature
- If you’re exercising outside for more than 2 hours or at a high intensity, drink about 16-32 oz. of Active Hydration per hour
- Monitor your urine. If it’s darker than light yellow, drink more fluids