Flying for long hours does not only cause fatigue but can also be dangerous. In some cases doctors found that flying on an airplane for several hours can cause deep-vein thrombosis, a potentially serious condition in which blood clots form in the leg or pelvic veins.
The risk is greatest for people with health conditions that promote clotting, such as cardiovascular disease, cancer and blood-clotting disorders, according to the World Health Organization. Being pregnant, having recently had surgery, taking hormonal medication, or being over 40 increases the odds, WHO states.
Doctors say that many air travellers who develop deep-vein thrombosis, or DVT, either did not have medical risk factors or did not think they had any. At least 200 people around the world have had DVT following air travel in the last decade.