CHICAGO Many of the effects of long-distance flight may be the result of altitude sickness rather than fatigue or jet lag, experiments carried out by Boeing doctors suggest.

Headache, nausea and dizziness, fatigue and a general feeling of malaise are symptoms of acute mountain sickness, which 75 per cent of people will experience at altitudes of more than 10,000ft (3,000m).

Aircraft fly much higher, but are generally pressurised to a minimum of 565mm of mercury, equivalent to an altitude of about 8,000ft, when flying at their maximum height. Pressure at ground level is 760mm.

A team led by Michael Muhm, of Boeing, recruited 500 healthy volunteers and asked them to spend several hours in a low-pressure chamber designed to simulate the pressure at various altitudes up to 8,000ft.

They report in the New England Journal of Medicine that symptoms of acute mountain sickness were experienced by 7.4 per cent of the volunteers. People above the age of 60 were less likely to report symptoms than younger ones, and men less likely than women.

The most common complaints were of backache, headache, light-headedness, shortness of breath and impaired coordination.

Explore Health

• Expert Advice

• Health Features

• Mental Health

• Alternative Medicine

• Child Health

• Health Club