Doctors say that sitting for long periods of time causes the condition, which kills 60,000 Americans each year. Clots are a serious concern for Paul Travis. He flies four times a year, but under doctor's orders he seldom stays in his seat. Well that's a lot, but it's necessary. Air travel is not Travis' only concern.
Clots can form while riding in a car or sitting at a desk.
But Francis believes air passengers are more at risk because in pressurized cabins it can be harder to breath. Low humidity causes dehydration and it is made worse when people drink too little water and too much alcohol. Wassman says that the airlines he represents are taking action, providing brochures, in-flight magazine articles and videotapes that talk about DVT and show passengers exercises that can help prevent it. However, the airlines say that with so little research, it's impossible to blame DVT on air travel. Still, one London hospital near Heathrow Airport has been averaging one death every month from passengers who develop clots on long flights.