Hydration in the mountains: The impact of cold and dry weather
Hydration at altitude is key to maintaining your energy level
Fatigue, headaches , dry mouth , body aches , cramps... These symptoms of dehydration are known, but often associated with high heat. However, the mountain climate is not exempt from this risk and, on the contrary, it is a very common phenomenon because the feeling of thirst is often less present during cold and dry weather while our water needs are in no way reduced. .
An aggressive mountain climate
In general, the temperature depends on the atmospheric pressure. The higher the pressure, the higher the temperature.
When we rise in altitude, the pressure decreases: the air must then expand to maintain the same volume, which costs it heat, so it cools. Because of this effect, the temperature decreases by 8°C per kilometer of altitude. As cold air can hold much less humidity than warm air, air humidity is halved for every 2 km of altitude.
The air in the mountain climate is therefore often very cold and dry .
Added to this is increased exposure to the wind as it rushes violently into the passes where it can pass freely: this is the Ventury effect , also called the tunnel effect. The wind increases the evaporation of perspiration and dries out the skin, leading to a state of dehydration.
Multiple effects on hydration
Body hydration is the result of a balance between water intake (drink) and water loss from the body. The latter come from four phenomena and are all affected by the mountain climate .
First, the contact of air with the skin produces natural evaporation : part of the water contained in the epidermis evaporates.
Cold, dry air and strong winds lead to greater dermal water loss in the mountains. The body, in response to the cold, constricts the blood vessels of the hypodermis. This results in a lower supply of water to the epidermis. This results in dry and dehydrated skin, particularly when it is thin (lips, hands, etc.): these are chapped skin. Proper hydration helps prevent the appearance of this skin dryness.
We lose about 1 glass of water (»250-300 mL) per day, at rest, by breathing .
During inspiration , the inspired air is warmed and humidified as it passes through the nose and upper airways. There is a rapid transfer of heat and water from the mucous membrane of the respiratory tract to the air. Thus, the air that reaches the pulmonary alveoli is always warmed (37°C) and saturated with water vapor (relative humidity of 100%).
During exhalation , some of the heat and water are taken up by the mucous membrane of the upper airways.
In a cold, dry climate , despite the fact that the airways are able to recover a greater percentage of heat and water transferred to the inspired air, the total heat and water loss in the exhaled air is more important.
In addition, the higher you go in altitude, the more the oxygen pressure decreases. With each breath we therefore bring less oxygen to our cells: this is hypoxia . In response to this, breathing intensifies – hyperventilation – to bring oxygen to the lungs, which increases water loss through the airways and promotes dehydration.
In the mountains, it is therefore necessary to compensate for these water losses and not to forget to hydrate to replace electrolytes and liquids.
Diuresis is the elimination of urine by the body, the product of blood filtration by the kidneys. When the cold drives the blood out of the extremities, this mechanically produces an influx of circulating blood, which passes through the kidneys and results in the production of urine. The increase in blood pressure also makes you want to urinate: liquids are lost more quickly through urine – this loss must therefore be compensated by more frequent water intake.
Sweating helps regulate body temperature by eliminating excess heat through the evaporation of body water. If the ambient cold makes it possible to cool the body better, the warm and waterproof outfits often worn in winter in the mountains (for winter sports) prevent the evacuation of perspiration and cause more abundant sweating - and therefore a risk of dehydration.
In summer, the wind and the dryness of the air give the deceptive sensation of not sweating because perspiration is directly evacuated.
It is noted that the water losses by these four mechanisms are more important because of the mountain climate , leading to a state of dehydration of the body and the symptoms which are associated with it and, consequently, an increased need for hydration .
Added to this is the fact that the cold reduces the feeling of thirst. Although the water losses are higher, we are tempted to drink less!
Physical activity in the mountains
A stay in the mountains is often an opportunity for physical activity, such as hiking, mountaineering, climbing, winter sports... Our hydration needs are doubly increased , by physical activity and by the climate. cold and dry described above. Fatigue, headaches, body aches, cramps due to dehydration can quickly disrupt a hike.
Dehydration is also an indirect cause of mountain accidents and injuries because it can cause states of weakness or confusion and make the body more sensitive to hypothermia.
To prevent the consequences of dehydration in order to avoid putting yourself in danger or spoiling your stay, you must be well hydrated , before, during and after exercise and use a drink rich in electrolytes.
Proper hydration is one of the keys to a successful ascent!
A few tips
Drink enough water , even without feeling thirsty, remains the first tip!
Always have an insulated bottle on you or in your backpack with cold or hot water.
It is also recommended to wear breathable clothing , or in layers that can be adapted to the effort in order to limit perspiration, to protect the skin of your face and extremities from the cold and wind, and to breathe through a scarf. to limit water loss.
Finally, the hydrolipidic films of moisturizing creams and balms limit the evaporation of water from the skin. They allow, for the first, to protect the sensitive areas from dehydration and for the second, to repair them.