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
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
- 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
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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