A new Netherlands study of blood clots has shown that travelling for more than four hours by air, car, bus or train can all increase the risk of blood clots, with air travel no worse than the others. The Dutch team studied 2,000 people who had suffered a venous thrombosis — a blood clot in a vein — for the first time. They found that 233 of them had travelled for more than four hours in the eight weeks preceding the event. Travelling doubled the chances of having a venous thrombosis. The hazard was greatest in the first week after travelling, and the overall risk of flying was no worse than that of going by car, bus or train. Particular groups of people, especially women on the Pill, were more at risk than others, and the risk was increased almost tenfold for people who were obese, and fourfold for individuals who were more than 6ft 3in (1.90m) tall. And if you are short, like the Beetle, the researchers found that being shorter than 5ft 3in was associated with a fivefold increased risk of thrombosis after air travel.