Many people associate dehydration only with exercising in hot environments. Sure this can certainly be true, but dehydration is also a common concern when exercising in the cold. It is in fact necessary to maintain hydration in the cold as much as in the heat, perhaps even more.
One obvious factor that could promote dehydration while exercising in the winter has to do with over-dressing for the conditions. Exercising in the cold with too much or the wrong type of clothing can lead to increased heat stress. This warm microclimate around the body can cause excessive sweating and overheating to levels similar to exercise in the heat. Therefore, it is important to dress appropriately.
Altered thirst sensation in winter
One important factor to consider when exercising in the cold is that our bodies have a decreased perception of thirst when in cold environments. Therefore, athletes exercising in the cold need to be extra vigilant to maintain good hydration habits.
Increased water loss in winter
Many times when individuals exercise in the cold for winter sports, it is at a higher altitude than normal. Relative to exercise at sea level, the same exercise at altitude results in increased ventilation to maintain blood oxygenation. Increased ventilation promotes dehydration because our breath is saturated with water, and so increased breathing results in increased water loss.
Alterations in perception of dehydration in the cold
Other than the decrease in thirst in the cold, there is also an alteration in the brain’s perception of dehydration in the cold. This effect can be explained in part by the redistribution of blood volume. To maintain core temperature in the cold, our bodies constrict blood from the periphery (arms, legs, and skin) to maintain the warm blood around the core of our body. In the cold, despite dehydration, central blood volume shifts prevent the increase in plasma AVP (AVP – also known as anti-diuretic hormone) relative to the same amount of dehydration in a warm environment. This results in increased urine production, promoting dehydration. Therefore, athletes exercising in the cold often have increased urine production compared to a more temperate environment. These changes result in an increased risk of dehydration in the cold that are not always obvious.
Other than dressing properly to not over- or under-heat, athletes need to be aware they will have increased water loss and decreased thirst while exercising in the cold. All the same principles for maximal exercise performance exist in both cold and warm environments. These principles include making sure to start exercise in a hydrated state, and consuming enough fluids during exercise to prevent dehydration and the decrease in performance it brings.