High altitude trekking brings its own rewards but your body may struggle to cope with the environment. Find out how your body adapts and how to prevent the symptoms of acute mountain sickness (AMS).

Mountain sickness

Trekking through the Himalayan or South American mountain ranges brings the rewards of awesome scenery and nature at its best. However these places are not the natural habitat for humans. Even at lower levels, most people succumb to acute mountain sickness (AMS). The main symptoms are headaches, tremendous tiredness, diarrhoea, weak legs and arms and sometimes sickness. They usually develop 6-12 hours after exposure to altitude above 3000m (9842 feet) and can be really severe after 48 hours. These are not pleasant symptoms when the aim of your adventure is to enjoy the stunning views of the world's highest peaks as you trek through the local villages. Even experienced climbers reckon they need around three weeks of acclimatisation before they feel anything like climbing.

The best advice for trekking at high altitude is to take it slowly. In Tanzania, the porters who accompany you up Kilimanjaro are constantly muttering the words 'pole, pole' (pronounced polee, polee). In Swahili this simply means 'slowly, slowly'. Another piece of advice is to drink enough water each day to prevent dehydration. With an increased rate of breathing, dry air is being inhaled but moist air exhaled - and this can mean an increased need for fluid. In the text books, this is usually quoted as three litres. While working at Everest Base camp, I monitored my fluid intake and found I was swallowing seven litres a day to keep hydrated!

Descend!

The pounding headaches of AMS are caused by an imbalance of fluid in the body, which occurs at altitude. Whilst fluid is lost from the bloodstream, it is retained in the brain, which becomes swollen. The extra pressure in this sensitive organ is felt as a thumping headache. This can affect your mood and it is common to have times of intense apathy interrupted by outbursts of intense irritability. The treatment of AMS is simple - go down. Descending to a lower altitude will give your system a chance to re-acclimatise. Moving to a higher altitude the second time around is often much more pleasant.
As a last resort, the prescription drug acetazolamide (Diamox) can be very effective in reducing the symptoms of AMS. It helps to re-balance the acid-alkali balance of the blood and is a diuretic. In this way it counteracts fluid retention, especially in the brain. Most doctors will tell you to start taking it as soon as you land at the airport. This is not necessary. Wait until you begin to get a slight headache. Diamox is absorbed very quickly and starts working its magic almost immediately. It does have side effects though. Expect a slight tingling sensation in your fingers or toes - this will go away as soon as you stop taking the drug.

If you suffer from AMS, you may not feel like eating - most people experience some loss of appetite, and weight, at altitude. Others can develop food cravings and an aversion to fatty, greasy foods. From my own research on food intake at high altitude, I found that my volunteers were eating less fat and more carbohydrate the higher they went. This is a useful switch since carbohydrate needs less oxygen to burn and produce energy, compared with fat. The local Sherpas and porters eat the perfect diet (plenty of rice, boiled potatoes, chapatis, lentils, beans) to fuel their work at high altitude.

Unfortunately, many of the Nepalese tea houses now cater for Western tastes and serve up deep fried chips, Yak burgers and apple pie - which have a high fat content. If you go trekking at high altitude, enjoy the local scenery - and eat the local diet.