Hydration at altitude is key to maintaining energy levels.
Fatigue, headaches , dry mouth , aches , cramps... These symptoms of dehydration are well-known, but often associated with high temperatures. However, mountain climates are not immune to this risk and, on the contrary, it is a very common phenomenon because the sensation of thirst is often less pronounced in cold and dry weather, even though our hydration needs are not diminished at all.
An aggressive mountain climate
Generally speaking, temperature depends on atmospheric pressure. The higher the pressure, the higher the temperature.
As altitude increases, pressure decreases: the air must then expand to maintain the same volume, which costs it heat, and therefore it cools down. Because of this effect, the temperature decreases by 8°C per kilometer of altitude. Since cold air can hold much less moisture than warm air, the humidity is halved every 2 km of altitude.
The air in mountain climates is therefore often very cold and dry .
In addition, there is increased exposure to the wind, as it rushes violently through the mountain passes where it can pass freely: this is the Venturi effect , also known as the tunnel effect. The wind increases the evaporation of perspiration and dries out the skin, leading to dehydration.
Multiple effects on hydration
Body hydration is the result of a balance between water intake (drinking) and water loss. The latter stems from four phenomena and is all affected by the mountain climate .
Firstly, the contact of air with the skin produces natural evaporation : some of the water contained in the epidermis evaporates.
Cold, dry air and strong winds lead to greater water loss through the skin in the mountains. In response to the cold, the body constricts the blood vessels in the hypodermis. This results in less water reaching the epidermis, leading to dry, dehydrated skin, especially on thin skin (lips, hands, etc.): this is chapped skin. Proper hydration helps prevent this dryness.
We lose about 1 glass of water (250-300 mL) per day, at rest, through respiration .
During inhalation , the inhaled air is warmed and humidified as it passes through the nose and upper airways. A rapid transfer of heat and moisture occurs from the respiratory tract lining to the air. Thus, the air reaching the alveoli of the lungs is always warm (37°C) and saturated with water vapor (100% relative humidity).
During exhalation , some of the heat and water are reabsorbed by the mucous membrane of the upper airways.
In a cold and dry climate , despite the fact that the respiratory tract is able to recover a greater percentage of heat and water transferred to the inhaled air, the total loss of heat and water in the exhaled air is greater.
Furthermore, the higher the altitude, the lower the oxygen pressure. With each breath, we therefore deliver less oxygen to our cells: this is hypoxia . In response, breathing intensifies – hyperventilation – to deliver oxygen to the lungs, which increases water loss through the respiratory system and promotes dehydration.
In the mountains, it is therefore necessary to compensate for these water losses and not forget to hydrate to replace electrolytes and fluids.
Diuresis is the elimination of urine from the body, a product of the kidneys' filtration of blood. When cold weather causes blood to drain from the extremities, this mechanically produces an influx of circulating blood, which passes through the kidneys and results in urine production. Increased blood pressure also creates the urge to urinate: this leads to a more rapid loss of fluids through urine – this loss must therefore be compensated for by drinking more water.
Sweating helps regulate body temperature by eliminating excess heat through the evaporation of body water. While the ambient cold helps cool the body more effectively, the warm, waterproof clothing often worn in winter in the mountains (for winter sports) prevents perspiration from evaporating, leading to increased sweating – and therefore a risk of dehydration.
In summer, the wind and dry air give the deceptive sensation of not sweating because the perspiration is directly evacuated.
It is observed that water losses through these four mechanisms are greater due to the mountain climate , leading to a state of dehydration of the body and the symptoms associated with it and, consequently, an increased need for hydration .
In addition, cold weather reduces the sensation of thirst. Although water loss is greater, we are tempted to drink less!
Physical activity in the mountains
A trip to the mountains often provides opportunities for physical activities such as hiking, mountaineering, climbing, and winter sports. Our hydration needs are doubly increased by physical activity and the cold, dry climate described above. Fatigue, headaches, muscle aches, and cramps due to dehydration can quickly disrupt a hike.
Dehydration is also an indirect cause of mountain accidents and injuries because it can lead to states of weakness or confusion and make the body more susceptible to hypothermia.
To prevent the consequences of dehydration and avoid putting yourself in danger or ruining your stay, you must stay well hydrated before, during and after exercise and use a drink rich in electrolytes.
Proper hydration is one of the keys to a successful climb!
Some tips
Drinking enough water , even without feeling thirsty, remains the first piece of advice!
Always carry an insulated water bottle with you or in your backpack filled with fresh or hot water.
It is also recommended to wear breathable clothing , or 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 in moisturizing creams and balms limit the evaporation of water from the skin. The former protects sensitive areas from dehydration, while the latter helps repair them.
