High altitude trekking & altitude sickness

Think of the world’s top trekking destinations, what comes to mind are mountains. These places provide unparalleled opportunities to lose yourself amid truly wild landscapes: rocky folds, forest blanketed lower slopes, the wilderness above the tree line, the chilly finger of a glacier edging down. They promise stunning views from summits, perhaps a caldera. Their rough terrain means they are free of roads, of houses, of offices, of all the things we wish to escape when we walk.
But by their very nature they also involve altitude. And anyone who has ventured to these heights will know this gives mountain trekking an extra dimension. The thin air can make for deep blue skies, clear views and striking photographs, but it also reduces the amount of oxygen you are breathing in, which can turn an already challenging trek into a real battle of wills. It’s tough to predict how you will feel and even tougher to prepare for, but it does mean that reaching a summit or crossing a high pass is all the more of an achievement; it also means that you’ll feel pretty much superhuman once you return to a low altitude to celebrate your victory. And so you should.

The science bit

Quite simply, the higher you go, the thinner the air is, meaning there is less oxygen available. You may notice a little breathlessness anywhere from 1,500m, but it tends to kick in around 2,400m. It is very hard to determine who will suffer from altitude sickness – also known as Acute Mountain Sickness (AMS) and it is almost impossible to prepare for. Fitness, age and health seem to have little impact on the symptoms, and even someone who has been fine at altitude on one occasion might feel absolutely dire the next. The only people who seem immune are those who have genetically adapted to life at high altitudes, in places such as Tibet, Ethiopia and the high Andes. Studies have shown that they have evolved to have higher breathing rates, larger lungs and the ability to carry more oxygen in each red blood cell. It’s no coincidence that Sherpas are able to summit Everest multiple times, and Ethiopians are record breaking athletes.
The first thing you are likely to notice is feeling out of breath, and taking a long time to get your breath back even if you stop walking. Headaches and dizziness are common, and you may also feel nauseous or vomit, particularly if pushing yourself physically. You’ll feel tired, although some people report being unable to sleep at altitude, no matter how exhausted they feel. This is also due to symptoms worsening at night. Some people also suffer from nosebleeds.
These symptoms are all unpleasant, and indicate that you should slow down, but they are not usually an indicator of anything serious. However, if ascending to high altitudes of between 3,500m and 5,000m, especially if you do so quickly, you must be aware that AMS can have severe consequences, the most serious being fluid in the lungs and swelling of the brain. Symptoms of these include those similar to bronchitis, with a dry cough (which may later produce blood), shortness of breath (even when resting) and chest pains. Fluid on the brain is characterised by a persistent headache, dizziness and confusion, nausea and vomiting. It can eventually result in a loss of consciousness. In rare and extreme cases, AMS can kill. If you experience any of these symptoms, tell your guide immediately, and descend as far as possible.

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Ladakh mountains trekking adventure

Ladakh mountains trekking adventure

Hike in N.India's Himalya, visiting Tibetan Monasteries.

From US $2399 9 days ex flights
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2024: 13 Jul
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Combating altitude sickness

There are a number of ways in which you can soften the impacts of altitude on your body, and happily, most tours will incorporate these to ensure travelers get the most out of their vacations.
Acclimatise. If you are planning to trek at high altitude, spend as long as possible acclimatising before your trek begins. This usually entails spending a couple of days at altitude but without physical exertion – such as in Cuzco (3,400m), before embarking on the Inca Trail. This gives your body the time it needs produce additional red blood cells to counteract the reduced amount of oxygen. The higher you go, the more acclimatisation is needed; climbers attempting to reach the summit of Mount Everest (8,848m) will spend several weeks acclimatising at Base Camp (5,364m). Climb high, sleep low. Most trekking routes will climb high during the day, then descend in the evening to ensure you are sleeping a few hundred metres lower. This is much easier on the body as you build up resistance gradually, and it means you are much more likely to get a decent night’s sleep. Generally, you should sleep no more than 300m higher each night, even if ascending further during the day. Go slow. Interestingly, the people who are most often at risk of succumbing to AMS are the fittest ones. This is because they are more likely to push themselves and head up much too fast. As altitude sickness does not distinguish between the fit and the unfit, those who climb without giving their bodies time to acclimatise are much more susceptible to it. If you do feel rough, speak to your guide. Responsible and qualified trekking guides will be able to advise you on how to proceed, can keep an eye on your symptoms, and will lead you down if they think it is necessary. Choose a longer tour. Another way to ensure you slow your ascent is to book onto a longer trip. This does mean using more vacation time, as well as paying a bit more, but if you make it to the top – rather than throwing in the towel halfway up – it will really be worth it. Even if you’re not attempting a summit, a slower climb is going to leave you feeling much better, and you’ll have a much more enjoyable vacation. A good example of this is on Mount Kilimanjaro; one of our tour operators has a 97 percent success rate of reaching the summit via the eight-day Lemosho Route, and 76 percent on the six-day Rongai Route. They don’t run the shortest, five-day route; operators that do have reported just a 27 percent success rate. Avoid the booze. Alcohol hits hard at altitude. You’ll get drunk fast, which can be a little scary when you’re used to knowing your limits. Worse, though, is the ensuing hangover. Altitude sickness can feel a little like being hungover anyway, so when combined with the real thing, it is brutal – with pounding headaches and nausea. If you’re unlucky, it might even stretch out to two days. This is unpleasant in any situation, of course, but particularly so if you have a day’s trek ahead of you. The best thing to do is avoid alcohol altogether – and plan a nice celebration when you get back down the mountain. Eat light meals. There’s a good chance you won’t feel like eating too much anyway, but heavy meals can make you even more tired and nauseous. Eat smaller, lighter meals, with energy boosting snacks in between times if necessary. And keep very well hydrated. Consider taking drugs. Diamox is an altitude sickness medication that can speed up acclimatisation. It’s not a substitute for any of the tips mentioned above, but is part of a multi pronged approach, particularly if flying directly into Lhasa, La Paz or Quito, for example, which gives you no time to acclimatise first. It is available without a prescription, but you may want to consult your GP before taking it. Some people also claim Ibuprofen can ease the headaches and nausea. In Bolivia and Peru, coca leaves are a traditional remedy; many travelers drink coca tea to combat symptoms.

Other things to watch out for at altitude


The thin air up in the mountains mean that UV rays penetrate more easily and are much more harmful. Compounding this, many trekking destinations are in tropical latitudes – including the Himalayas and most of the Andes – or even on the equator, including Kilimanjaro and the Ecuadorian Andes. However, the air is chilly up there, and many people fail to protect themselves as they don’t associate cold temperatures with sun burn. You can burn in minutes up here though, so be sure to cover up, wear a hat and slap on the Factor 50.

Exploding liquids

The low air pressure at altitude is similar to that on a plane. The pressure inside sealed containers is higher as a result, so expect bulging water bottles, but also exploding toiletries and pens. Screw lids on tightly, and maybe even release the pressure little by little as you go up to avoid leaks. Ziploc bags can help contain the mess; bar soaps and stick deodorants also prevent mishaps. In Bolivia, some beers are produced at lower pressure for drinking in the Andes (so they don’t erupt when you open them) and at higher pressure for drinking in the low altitude tropics. This is known as ‘tropicalizada’ (‘tropicalised’) – don’t accidentally open one of these at 3,800m in La Paz!
Written by Vicki Brown
Photo credits: [Page banner: DMSU] [Sickness intro: Carlos Gracia] [The science bit: Azlan DuPree] [Symptoms: Steve Hicks] [Symptoms 2: Steve Hicks] [Sunburn: Nick Jewell] [Exploding liquids: Martin Lang]