Sitting still for long periods cannot alone explain why air passengers are at higher risk of potentially deadly blood clots, research suggests.

The risk of developing deep vein thrombosis is thought to be raised by air travel - particularly long flights.

But a Lancet study by Dutch researchers found chemicals indicating clotting in 71 volunteers were higher during eight hours on a flight than in the cinema.

It suggests low air pressure and oxygen levels on a flight may play a role.

http://news.bbc.co.uk/2/hi/health/4788774.stm