The health effect of most recent concern, though, is the development of a deep vein thrombosis (a blood clot in a deep vein of the thigh or calf) after long flights. Deep vein thrombosis is a common medical condition in the general population. It can be caused by a narrowed or blocked vein which increases the risk for clotting.

The complication of urgent concern with deep vein thrombosis is the onset of a pulmonary embolism, brought on by the blot clot traveling from the leg vein to the lung (where it subsequently blocks an artery). Many of the recent deaths from air travel have been through a pulmonary embolus.

See: Deep Vein Thrombosis. British United Provident Association (BUPA).