Acclimatisation to altitude: how to best adapt to high peaks

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Have you always dreamed of exploring the highest peaks of the Alps and their breathtaking panoramas? If so, then you need to prepare yourself by acclimatising to the altitude. It's a complex process, but good preparation can make all the difference.

Acclimatation altitude - comment s'adapter au mieux aux grands sommets

We will provide you with valuable information on acclimatisation methods, recommended lifestyle habits, suitable supplements and the warning signs of altitude sickness. With this advice, you will be able to enjoy your high-altitude adventure to the fullest while minimising any negative effects on your health.

Summary:

What is the high altitude environment?
What is altitude acclimatisation?
The effects of altitude on the human body and lack of oxygen (hypoxia)
The symptoms of altitude sickness
The importance of acclimatisation before a high altitude climb
How to acclimatise to altitude?
How long do the benefits of altitude acclimatisation last?
Common mistakes to avoid when acclimatising to altitude
Our mountaineering courses to help you acclimatise for a 4,000-metre peak in the Alps
Conclusion

What is the high-altitude environment?

environnement d'altitude

The high-altitude environment and its characteristics as seen by the Montagne Altitude Santé team ©Perceptiom scientific outreach agency

Before addressing the issue of acclimatisation, we need to look at when we can talk about a high-altitude environment and what its characteristics are.

We generally refer to an altitude environment as being above 1,500 metres above sea level. However, the effects of altitude become truly significant above 2,500 metres.

Altitude classification

Moderate altitude: 1,500–2,500 m (e.g. medium mountains)

High altitude: 2,500–3,500 m (e.g. Alps, Andes)

Very high altitude: 3,500–5,500 m (e.g. Himalayas, Peruvian Andes)

Extreme zone: Above 5,500 m (e.g. Himalayan peaks)

What are the characteristics of a high-altitude environment?

1. Lower atmospheric pressure and less oxygen available

The higher you climb, the less oxygen there is.
This can cause breathing difficulties and acute mountain sickness.

2. Lower temperatures

The air loses an average of 6.5°C for every 1,000 metres of altitude.
There are significant temperature differences between day and night.

3. Increased solar radiation

There is less atmosphere to filter UV rays, increasing the risk of sunburn and snow blindness.
UV solar radiation increases by 10% every 300 metres.

4. Drier air and rapid dehydration

Air humidity decreases, causing dry skin and mucous membranes.

5. Extreme weather conditions

Strong winds and snowfall.
Frequent freeze-thaw phenomena.

6. Poor soil and rapid erosion

Limited vegetation depending on altitude:

Mountain forests below 2,500 metres.
Alpine meadows between 2,500 and 3,500 metres.
Rocks and glaciers above 3,500 metres; very mineral environment.

7. Adaptations of fauna and flora

Plants with thick leaves and slower growth.
Animals with dense fur, more developed lungs or adapted metabolism (e.g. yaks, ibex).

A high-altitude environment is therefore a challenging one, requiring specific physiological and ecological adaptations.

What is altitude acclimatisation?

Acclimatisation to altitude is a physiological process whereby the human body adjusts to changes in atmospheric pressure and the decrease in available oxygen as one climbs to higher altitudes. When you reach altitudes above 2,500 metres, atmospheric pressure decreases significantly, reducing the amount of oxygen you can inhale. To respond to this new reality, the body begins to adapt its vital functions in order to maintain sufficient oxygenation of the tissues. It is therefore generally above 2,500 metres, at high and very high altitudes, that the first effects on the human body begin to be felt.

Several mechanisms come into play during this process. First, the heart rate increases to pump more oxygen-rich blood to the muscles and organs. Next, breathing becomes faster and deeper to maximise oxygen intake. Finally, in the longer term, the body begins to produce more red blood cells, which are responsible for transporting oxygen. These adaptations can take several days or even weeks, depending on the individual and the altitude reached.

It is crucial to understand that acclimatisation is not an instantaneous process. Each person reacts differently to altitude, and some may experience difficulties even at relatively low altitudes. Therefore, good preparation and a thorough understanding of the mechanisms of acclimatisation are essential to minimise the risk of altitude-related illnesses, such as acute mountain sickness.

The effects of altitude on the human body and lack of oxygen (hypoxia)

effets de l'altitude

As altitude increases, the effects on the human body become more pronounced. One of the first changes observed is a decrease in oxygen pressure in the air. At high altitudes, such as those found in the Himalayas or the Andes, the air we breathe contains much less oxygen, which can lead to severe hypoxia, i.e. a significant lack of oxygen in the blood. But it is the brain that is most sensitive to this, and difficulties can begin to arise once the white zone has been passed (6 to 8 hours at high altitude).

This phenomenon can cause feelings of fatigue, headaches and decreased physical performance. Other effects, such as increased irritability, can also have a significant impact on group life or travel, for example.

The physiological effects of altitude are not limited to reduced oxygen levels. The body also undergoes changes in its water balance. At high altitudes, the air is often drier, and water loss through breathing and sweating can increase. In addition, dehydration can lead to decreased physical and mental performance, making acclimatisation even more difficult. It is therefore essential to ensure adequate hydration during ascents.

Finally, altitude can also have an impact on sleep. People at high altitudes may experience difficulty sleeping due to irregular breathing. These sleep disturbances can exacerbate the symptoms of altitude sickness and interfere with acclimatisation. Therefore, it is crucial to be aware of these effects and take steps to mitigate them when exploring high-altitude regions.

Here is a summary of the different effects that altitude can have on the human body depending on the altitude.

At 1,500 m - 2,000 m: First mild effects

Atmospheric pressure begins to decrease, but remains sufficient for most people.
Mild physiological effects:
- Very moderate decrease in blood oxygen saturation (normally >95%). People who are not accustomed to high altitudes may tire more quickly during exertion.
- Possible mild hyperventilation.
Easy acclimatisation for most people.

At 2,000 m - 3,000 m: Noticeable effects of oxygen deprivation begin to appear.

More pronounced hypoxia:
- Blood oxygen saturation may drop to around 90-93%.
- More rapid shortness of breath during physical exertion.
- Increased heart and respiratory rates to compensate.
Possibility of early symptoms of altitude sickness (in some people):
- Headaches, mild insomnia, possible nausea.
- Acclimatisation is necessary if ascending rapidly.

It is therefore generally at altitudes of 2,000–2,500 metres that the first signs of oxygen deprivation can be felt.

At 3,000 m - 4,000 m: Moderate to severe hypoxia

The oxygen available is approximately 68-70% of that at sea level.
Blood oxygen saturation can drop to 85-90%.
Common effects on the body:
- Shortness of breath even at rest.
- Decreased physical performance.
- Frequent insomnia, disturbed sleep.
- Acute mountain sickness possible (headaches, nausea, dizziness).
Acclimatisation necessary to avoid uncomfortable symptoms.

4,000 metres and above: Extreme conditions for the human body

Available oxygen is reduced to 60% or less.
Significant effects on the body:
- Extreme fatigue and constant shortness of breath.
- Decreased cognitive abilities (slowed reflexes, difficulty concentrating).
- Frequent acute mountain sickness without acclimatisation.
- Risk of pulmonary or cerebral oedema in some individuals.
Long acclimatisation and gradual ascent recommended.

What are the benefits of living at altitude?

bénéfices habitat moyenne altitude

We have seen that altitude can have negative effects on the human body, but when living at moderate altitudes, we can also reap benefits.

A scientific review suggests that living at moderate altitudes is associated with a decrease in mortality from cardiovascular disease, stroke and certain types of cancer, based on numerous separate measurements and studies conducted in different mid-altitude regions around the globe. In Switzerland, for example, the risk of stroke decreases by 12% for every 1,000 metres of altitude. It has also been noted that intermittent hypoxic stimulation (e.g. downhill skiing) may be a potential contributor to the beneficial effects on cardiovascular health.

However, an increase in mortality due to chronic obstructive pulmonary disease (COPD) and possibly lower respiratory tract infections has been observed.

It is therefore suggested that living at moderate altitudes may offer protective benefits, while higher altitudes may have adverse effects, particularly with regard to respiratory diseases. These findings highlight the importance of considering altitude of residence in the prevention and management of certain diseases.

The concept of the exposome, which encompasses all exposures to environmental (i.e., non-genetic) factors, must also be taken into account. The mid-altitude environment can thus have a positive impact on our health, with a lower incidence of disease.

Symptoms of altitude sickness

Altitude sickness, also known as acute mountain sickness (AMS), is a condition that can occur when the body is unable to adapt quickly to changes in altitude. Symptoms can vary in intensity and usually appear between 6 and 12 hours after ascending to a high altitude. The most common symptoms include headache, nausea, dizziness, and excessive fatigue.

Headaches are often the first sign of altitude sickness, and they can be quite intense. They are caused by vasodilation of the blood vessels in the brain in response to increased blood pressure. In addition to headaches, people may experience nausea and vomiting, which can make it difficult to consume food and water. Loss of appetite is also common, exacerbating the problem of dehydration.

Other symptoms may include sleep disturbances, rapid and shallow breathing, and a general feeling of malaise. In more severe cases, altitude sickness can progress to more serious conditions, such as high altitude cerebral oedema (HACE) or high altitude pulmonary oedema (HAPE), which require immediate medical attention. It is therefore essential to recognise these symptoms early and take appropriate action, such as descending to a lower altitude and resting.

You can also read our dedicated article to learn more about altitude sickness.

The importance of acclimatisation before climbing to high altitudes

importance acclimatation altitude

Acclimatisation plays a crucial role in preparing for a high-altitude climb. It allows the body to gradually adapt to harsh environmental conditions, thereby reducing the risk of altitude-related illnesses. By taking the time to acclimatise, climbers and hikers can improve their overall well-being and performance during their adventure.

Proper acclimatisation also helps to optimise hydration and nutrition, two essential elements for maintaining energy and vitality at altitude. By acclimatising slowly, the body learns to use oxygen more efficiently, which helps to minimise fatigue and improve endurance. Those who neglect this acclimatisation process may quickly feel exhausted and less able to perform, which can make their mountain experience less enjoyable.

In addition, proper acclimatisation helps to better manage the symptoms of altitude sickness. By allowing the body to adapt to high altitudes gradually, climbers can reduce the risk of developing serious complications. In short, acclimatisation is an essential element in ensuring the safety and success of a climb.

How long does it take to produce red blood cells at high altitude?

At high altitudes (above 2,000/2,500 metres), red blood cell production (erythropoiesis) accelerates in response to the decrease in available oxygen. Here are the typical stages:

Immediate reaction (hours to days): Upon exposure to altitude, the body detects the decrease in oxygen and increases the production of erythropoietin (EPO), a hormone that stimulates the bone marrow.
Increase in red blood cells (a few days to weeks): A significant increase in red blood cell count begins after 4 to 7 days and continues for 2 to 3 weeks.
Full adaptation (weeks to months): Maximum adaptation generally takes 3 to 6 weeks, or even several months, depending on the altitude and the individual.

This is why athletes often train at altitude for at least three weeks to fully benefit from the effect.

How can you acclimatise to high altitudes?

There are several methods to promote effective acclimatisation to altitude. The first and most important is to ascend gradually. This means that you should avoid climbing too quickly to high altitudes. A general rule of thumb is not to increase your altitude by more than 300 to 500 metres per day once you exceed 2,500 metres. This allows your body to slowly adapt to changes in atmospheric pressure and oxygenation.

Another effective method is to take rest days at intermediate altitudes. For example, if you are planning an ascent to a summit above 4,000 metres, it may be beneficial to spend 2 to 3 days at an altitude of 3,000 metres to allow your body to acclimatise. This may seem counterintuitive, but taking the time to acclimatise can significantly improve your performance during the final ascent. Spending a night resting in a refuge at 2,500/3,000 metres is therefore more effective for acclimatisation than making a ‘dry’ ascent to 4,000 metres and returning to the valley in a single day. These rest periods also allow you to monitor the symptoms of altitude sickness and react quickly if necessary.

Nutrition and hydration during altitude acclimatisation

hydratation et nutrition en altitude

Nutrition and hydration play an essential role in the process of acclimatisation to altitude. At high altitudes, the body needs an increased energy intake to cope with physical exertion and the additional demands of acclimatisation. It is therefore crucial to eat foods rich in carbohydrates, which provide a quick and easily available source of energy. Choose foods that are easy to digest, such as pasta, rice and fruit. In general, at altitude, the digestive system is put under strain, so it is important to find a source of energy without overloading the stomach. Also be careful with food, which can be of poor quality at high altitudes (as supplies and choices are limited) and can cause traveller's diarrhoea, especially in Andean and Himalayan countries.

Hydration is just as important. As you climb higher, dehydration can set in more quickly due to the dry air and increased water loss. It is recommended that you drink regularly, even if you are not thirsty, to maintain adequate hydration levels. Water is essential, but you may also want to consider consuming electrolyte drinks to replace minerals lost through perspiration. Scientists have shown that the body loses up to 1900ml/day of water through respiration for men and 850ml/day for women at altitudes above 2500m, whereas in low/moderate conditions and altitudes, this is only 250 to 300ml/day. Total fluid intake at high altitude is therefore around 3 to 4 litres per day to promote optimal kidney function and maintain a urine output of approximately 1.4 litres in adults.

Finally, it is important to pay attention to your body's signals. If you experience excessive fatigue or symptoms of altitude sickness, it may be helpful to adjust your diet and hydration accordingly. Good nutrition and adequate hydration can make all the difference in your acclimatisation and your ability to fully enjoy your high-altitude adventure. And if you are in a group, make a point of checking in with each other regularly to keep an eye on one another.

How long do the benefits of altitude acclimatisation last?

durée bénéfices altitude

After a prolonged stay at altitude (at least 1-2 weeks), the adaptations gradually diminish once you return to lower altitudes, and disappear almost completely within 1-2 weeks. If you want to acclimatise to a high-altitude climb with an initial stay at altitude, you should do so as close as possible to your departure for high altitude. After several weeks back at sea level, if you are planning another trip to high altitude, you will need to go through the entire acclimatisation process again.

To acclimatise as well as possible for a climb in the Alps above 4,000 metres, we recommend acclimatising with a night or two in a refuge above 2,500 metres in the days leading up to the start of the climb, and no later than 2 to 3 weeks before.

Common mistakes to avoid when acclimatising to altitude

erreurs acclimatation altitude

When acclimatising to altitude, certain common mistakes can compromise your health and safety. One of the most common mistakes is neglecting the acclimatisation period. Many hikers and climbers, eager to reach their goal, choose to climb too quickly. This can lead to severe symptoms of altitude sickness and, in some cases, life-threatening complications. It is therefore essential to maintain a slow pace and listen to your body's signals.

Another common mistake is underestimating the importance of hydration. At high altitudes, water loss can be significant, but many people forget to drink enough. Dehydration can exacerbate the symptoms of altitude sickness and reduce your physical performance. It is crucial to keep a bottle of water handy and drink regularly, even if you do not feel intensely thirsty. Ignoring your body's signals is a mistake that can have serious consequences.

If you experience persistent headaches, nausea, or increased fatigue, it is essential to take these symptoms seriously, as they are often symptomatic of altitude sickness. Ignoring these signals can lead to a worsening of your condition. When in doubt, descending to a lower altitude and resting may be the best solution to ensure your safety.

Finally, be very careful with medications or treatments (such as Diamox or aspirin/ibuprofen) that are supposed to help you acclimatise better or alleviate certain effects of altitude. It is important to remember that these medications should be taken with great caution and under medical supervision.

Our mountaineering courses to help you acclimatise for a 4,000-metre peak in the Alps

Esprit Montagne offers numerous mountaineering courses in the Alps, but if you want to climb your first 4,000-metre peak while acclimatising as well as possible or explore new summits, some of our courses are more suitable than others. For example, you could attempt to climb Gran Paradiso, with a night in a refuge at 2,700 metres and a summit at 4,061 metres, which is ideal for testing yourself. It is also possible to combine Gran Paradiso with the ascent of Monte Rosa and Punta Gnifetti (4,554 metres) for a four-day adventure. Finally, the ascent of Mont Blanc can also be done with a 4-day acclimatisation period, where you will spend 2 nights at an altitude of over 3,000 metres before attempting the final ascent to the summit.

Conclusion

Acclimatisation to altitude is an essential process for anyone wishing to explore high peaks. By understanding the effects of altitude on the human body and adopting appropriate methods to acclimatise, you can reduce the risk of altitude-related illnesses and enjoy your adventure to the full. The key lies in adequate preparation, paying close attention to your nutrition and hydration, and listening carefully to your body's signals.

By following these tips and avoiding common mistakes, you will be well equipped to face the challenges of high altitude. Whether you are an experienced mountaineer or a novice hiker, proper acclimatisation will allow you to enjoy unforgettable moments in the mountains. Prepare to climb majestic peaks with confidence and savour every moment of this incredible high-altitude experience.

Article written by Adrien Ozanon

When science studies the world's highest population in Peru with the Expedition 5300 research programme

Launched in 2019, Expedition 5300 is a scientific programme led by Inserm, Grenoble Alpes University and Grenoble Alpes University Hospital under the direction of Samuel Vergès, Research Director at the HP2 laboratory and member of the Mountain Altitude Health Chair. Its objective is to study the impact of extreme altitude on human health, particularly in La Rinconada, the highest inhabited town in the world (5,300 m), where 50,000 people live in conditions normally considered incompatible with permanent residence.

At this altitude, oxygen is reduced by half, requiring the human body to adapt in unique ways, but also revealing its physiological limits. Gold miners in the region have haemoglobin levels of up to 20.3 g/dL, with haematocrits sometimes exceeding 80%, leading to hyperviscosity and extreme cardiac stress. Approximately 25% of the inhabitants suffer from chronic mountain sickness, a serious syndrome that affects blood circulation and cognitive functions. In 2023 and 2024, the programme was extended to include the study of 600 children living at altitude, in order to analyse the impacts of hypoxia on their growth, neurocognitive development and cardiovascular health. Each family received a personalised medical report, illustrating the social and ethical commitment of the mission.

The wealth of data collected during the eight scientific missions not only provides a better understanding of the mechanisms of adaptation to hypoxia, but also sheds valuable light on respiratory diseases in lowland areas and optimises support for trekkers and mountaineers at medium and high altitudes. Numerous scientific publications resulting from this work contribute to enriching our understanding of the limits of the human body in the face of oxygen deprivation.

To follow this adventure on hypoxia: www.expedition5300.com

To follow scientific advances and research work: montagne-altitude-sante.fr

Acclimatisation to altitude how to best adapt to high peaks