Researchers have begun a major study into the possible links between long-distance air travel and blood clots, doctors said Monday. While there is speculation that long-distance flights trigger blood clots, or deep vein thrombosis, "we want to find out how much of a problem that is," said researcher Dr. Sarah Hill.

The $102,000 study is a joint project between Auckland's Green Lane Hospital and Otago University's Wellington School of Medicine and Health Sciences.

The project will study up to 1,000 people taking flights of more than four hours duration who return within six weeks. Researchers will take blood samples for testing before and after travel to screen for clotting, Hill said.

Research leader Dr. Rodney Hughes said the study will look at a broad range of travelers, rather than the high-risk groups which have been the targets for previous research into deep vein thrombosis.

Reports of passengers dying from clots after long flights have mounted recently, leading to speculation that the flights could be to blame.