Article by Ruth McKean, Sports Nutritionist

6. Acute Mountain Sickness (Altitude Sickness)

It is now established that at altitude over 3000m acute mountain sickness is common in the unacclimatised individual. The speed of ascent and aerobic fitness are one of many factors in acute mountain sickness and the onset is normally within 6 hours. The symptoms (see below) are usually reduced after 3 days but the weight loss is usually not regained until a return to sea level.

Some people are unfortunate enough to experience a more severe aspect of acute mountain sickness called high altitude pulmonary oedema. This is a life threatening conditioning where fluid accumulates in the lungs and brain. To prevent severe disability or even death the best treatment is immediate descent to a lower altitude. If summating a peak in an organised group and you or anyone else start experiencing the signs of acute mountain sickness you should descend until you feel well again. Do not give in to peer pressure to finish the climb.

Symptoms of altitude sickness

  • Headache
  • Dizziness
  • Nausea
  • Loss of body weight is likely to be caused by an increase in basal metabolic rate and an energy imbalance
  • Dehydration may be indicated by drowsiness, impatience, discomfort, and weariness/ fatigue or a sluggish feeling and reduced work efficiency. Increased water and sweat losses will also increase risk of dehydration. For more information see page on fluid needs at high altitude.

In general, the acclimation period depends on the altitude. As a broad guideline about 2 weeks is required to adapt to an altitude of 2300m. Thereafter each 600m increase in altitude requires an additional week for full adaptation up to altitude of 4572m.

If athletes want to compete at altitude it is difficult to take part in hard training on arrival at altitude but intense training should commence as soon as possible to minimising any detraining period. The benefits of acclimation are likely to be lost within 2 or 3 weeks after returning to sea level.


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