The Daily Telegraph informs it's readers that flying long haul triples the passenger's risk of experiencing deep vein thrombosis. The paper cites a Dutch study in which 8,755 employees of international companies participated over a four year period. The average age of the subjects was 40.
Fifty three cases of DVT were recorded, 22 of which were within 8 weeks of a long haul flight, making an incidence rate of 3.2 cases per 1,000 people per year. This compares with 1 per 1,000 for non-flyers. That's still a pretty small risk (one clot in 4,656 long-haul flights) and perhaps not as alarming as the headline suggests; in fact the researchers just recommended taking blood thinning drugs such as aspirin as a precaution. Still, some readers may prefer the stocking option.