A study carried out in New Zealand found that a third of patients admitted to a hospital with deep vein thrombosis (DVT) had jobs that involved sitting still at desks for long periods.
DVT is the formation of a blood clot in a deep vein, most commonly in the legs. The clots can travel to the heart, lungs or brain, causing chest pain, breathlessness or possible death from a heart attack or stroke.
DVT affects around 100,000 people and kills between 500 and 1,000 in Britain each year. Passengers sitting on long-haul flights without space to stretch out were considered as most at risk.
But Prof Richard Beasley. of New Zealand's Medical Research Institute, found that a third - 34 per cent - of 62 patients aged under 65 admitted to a hospital with blood clots spent long periods of time seated as part of their jobs. This compared to 21 per cent who had recently travelled on a long-haul flight.
He said some office workers who developed clots sat at their screens for 14 hours a day.
"The risk is certainly there," he said. "There are considerably more people who are seated for long periods at work as part of their normal day than there are travelling."