A study by Professor Richard Beasley of the Medical Research Institute in Wellington found that a third of patients admitted to hospital with deep vein thrombosis (DVT) were office workers who spent long periods at a computer.

A total of 34 percent of the sample of 62 people admitted with blood clots had been seated at their desks for long periods, compared with 21 percent of patients who had recently travelled on long-distance flights, the New Zealand Herald newspaper reported.

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.

The condition has been dubbed "economy class syndrome" because passengers sitting on long-haul flights without space to stretch out were considered as most at risk.

Studies found clots formed in 10 percent of air travellers at high risk of the condition and one percent of all passengers.

Treatment is through blood thinning drugs which can take months.

Beasley said some office workers who developed clots sat at their screens for 14 hours a day.

"Some of them were going three to four hours at a time without getting up," he said.

The problem was most common in the information technology industry and in call-centres, he added.

The study is to be presented later this month at the annual conference of the Thoracic Society of Australia and New Zealand, and will also be published in the New Zealand Medical Journal.