However, the body makes and dissolves clots routinely and none of the clots in the study became a problem. Reports of passengers dying from clots after long flights have mounted recently, leading to speculation that the flights could be to blame. It may be that sitting in front of your computer for hours does the same thing. Experts estimate that every year, about one in 1,000 people is diagnosed with blood clots in leg veins. Clots occur when circulation slows, usually when people stay still for too long.
Some people have a genetic propensity to form clots too readily, and others acquire it.
The finding that 10 percent of the passengers developed a detectable clot may sound alarming, but experts said screening often picks up clots that prove to be harmless. Blood clots show up on ultrasounds in about 50 percent of surgical patients, but only about 10 percent of those people go on to develop a meaningful clot, said Dr. Robert McBane of the Mayo Clinic. The Lancet findings should be viewed with that in mind, said McBane, who was not involved with the research. If the actual risk really was 10 percent, that would be horrible. It must be overinflating the actual risk by at least a decimal point.