The study, by a team of Belfast researchers, found that oxygen levels fell by an average of four per cent when people reached cruising altitude.
84 passengers, aged from one to 78, had their oxygen saturation levels measured by qualified anaesthetists on the ground and at cruising altitude.
Ground levels averaged 97 per cent and these fell to an average of 93 per cent at altitude.
"We believe that these falling oxygen levels, together with factors such as dehydration, immobility and low humidity, could contribute to illness during and after flights" says Dr Susan Humphreys, Anaesthetic Specialist Registrar.
"This has become a greater problem in recent years as modern aeroplanes are able to cruise at much higher altitudes.
"The oxygen levels of 54 per cent of our subjects fell to less than 94 per cent at maximum altitude and an earlier study suggests that a third of physicians would put hospital patients with these levels on extra oxygen."
55 passengers were on long haul flights that lasted for more than two hours and the remaining 29 were on short haul flights. The measurements obtained from both groups were very similar. None of the subjects had severe cardio-respiratory problems and no-one required permission from their doctor to fly.
"The House of Lords and the Department of Transport have both acknowledged that more studies need to be carried out with respect to the effects of air travel on health, as there is little information on the physiological effects of flying on passengers currently available" adds Dr Rachel Deyermond, Consultant Anaesthetist.
"This is the first study to quantify the reduction of percentage oxygen saturation at high altitude during commercial air travel. It demonstrates that there is a significant fall in levels in all age groups during both short and long haul flights."
Further information and press copies of the paper are available from: Annette Whibley, Wizard Communications email@example.com
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