It is easy to associate dehydration with summer temperatures, hot and humid, when the sensation of thirst is more evident, but even the cold can accelerate this phenomenon in a less visible but no less risky way. In Winter, the loss of body fluids can be as high as that which occurs in the summer period, also because, in this season, it is easier to let your guard down and underestimate the phenomenon in question: you dehydrate through breathing and sweating. which, although less perceived, is favored by the use of heavier clothing and excessive air conditioning which reduces the humidity in the rooms.
It is estimated that breathing cold and dry air can increase the loss of body fluids through breathing by about 5 ml in an hour [1], a measure that may appear negligible for short periods, but which becomes significant when habitually living in environments cold for many hours a day.
During the warmer months, it is easier to drink the recommended amount of water - 8-10 glasses - while it becomes difficult to do so in winter. Thirst is a fundamental symptom of dehydration, which, however, is reduced by up to 40% during the colder months [2], even if our body's water needs do not change over the course of the year.
"We often underestimate that in the winter season the human body can be more exposed to the risk of running into a water deficit." Says Professor Alessandro Zanasi, expert at the Sanpellegrino Observatory and professor at the University of Bologna "The reason is due to a lower sensitivity of our organism to the stimulus of thirst, mainly due to the mechanism of" vasoconstriction ", put in place from our body in response to low external temperatures. "
This mechanism represents a contraction of veins and arteries that tends to reduce blood circulation in the peripheral and outermost areas of our body: in this way our body conserves the heat inside and keeps the temperature of the internal organs constant. A side effect, however, is to reduce the reactivity of our brain to the signals sent by the body, including in particular the stimulus of thirst.
“The sense of thirst is certainly an important alarm bell, used by our body to remind us that it is time to drink, but at the same time it is already a significant sign of dehydration and as such should even be anticipated. Proper hydration starts from the good habit of drinking often and constantly throughout the day, even in situations where the loss of fluids is apparently not significant. " Concludes Professor Zanasi.
There are other interacting factors - such as activity level, diet and health conditions that can affect how quickly the body loses fluid. This is why you still need to drink more when exercising or working outdoors.