Australian vascular specialists have backed calls by Indian medics to increase understanding of the dangers of deep vein thrombosis in land travel.

The medics from India's Government Medical College write in the latest Medical Journal of Australia of a fresh case of a 35-year-old man who developed DVT after a 14-hour train journey in cramped conditions.

"Any journey of more than four hours poses a risk for DVT," Professor Jeet Kashyap wrote, with people who are overweight, pregnant or on the oral contraceptive carrying an even greater risk.

"This case highlights the importance of considering all types of prolonged travel as potential risk factors for DVT."

Robert Lusby, a professor of vascular surgery at the University of Sydney, said the risk of land travel on DVT was poorly understood by Australians.

"Australia is a very big country so the risk posed by DVT, particularly in long distance car and bus travel, is very real," said Prof Lusby.

He said he had treated several cases of DVT caused by long bus trips, "and it's very likely we match India with cases on our trains".

"The risk is there for any travel where you sit for long periods with your knees bent and a lack of movement, which is, of course, the case on most of the bigger trips across our country."

Travel-related DVT, first identified in 1954, is the forming of leg clots caused by poor blood flow into the calf muscle.

Symptoms usually develop between one and eight weeks after a trip.

Prof Lusby said he advises people to stretch their legs wherever possible.

"On car journeys it's important to make the effort to stop and get out every hour or so just to get the blood circulating properly," he said.