Sometimes the last thing you feel like doing after returning from a run in the cold is hydrating. The same exact run in summer may have you headed straight to a cold drink, yet hydrating in winter is often forgotten as we often don’t feel thirsty.
The danger of not feeling as thirsty in winter is that it can lead to dehydration without the usual warning signs that we notice during warmer weather.
We lose a lot of water from our bodies in winter through respiratory fluid loss as a result of breathing in cold air. Cold air has less moisture than warm air, which means the lungs have to use moisture from our body when breathing.
It’s also easy to forget how hard we have to work while running in all those extra winter-layers. We’re still sweating, but it evaporates much faster in cold dry air. As a result, we often finish runs feeling as though we didn’t sweat a lot and therefore neglect proper hydration. This is despite the fact that fluid loss may have been the same as a run in warmer weather.
The science shows us that the same thirst mechanism which activates as a result of fluid loss in warmer temperatures does not produce the same response in cooler weather. This isn’t just because we don’t feel warm, rather, evidence suggests that the cold actually alters our thirst sensation.
Studies at the University of New Hampshire determined that when running in the cold the body decreases blood flow to the periphery of the body (extremities like your fingers and toes) to decrease heat loss. Blood is instead pushed to your core to look after your vital organs.
However, the brain doesn’t detect this increase in blood volume, and so despite elevated levels of sodium due to the fact that we are still sweating, our thirst sensation is reduced by up to 40%.
“It’s a trade off – maintaining the body’s core temperature becomes more important than fluid balance,” Professor Kenefick says.
“Humans don’t naturally hydrate themselves properly, and they can become very dehydrated in cold weather because there is little physiological stimulus to drink.”
Make sure to consume around 250mL / 8.5 ounces of fluid for every 30 minutes of running. For easy days or runs of 30 minutes or less water is just fine, but for more intense workouts or runs of over 60 minutes make sure to replace your electrolytes with your favourite flavour of SOS, either hot or cold.