The World Health Organisation today appealed for 12 million euros (£9.4 million) to finance studies on the link between air travel and deep vein thrombosis (DVT) - potentially fatal blood clots.
The UN health agency said in a statement that the research would take two and a half years to complete.
Medical officials from major airlines and other civil aviation experts meeting under WHO auspices last March recommended wide-ranging studies on the extent of the problem, often known as economy class syndrome .
Cases of DVT are blood clots that form in blood vessels in the leg. If a clot, or part of it, dislodges and moves to the lungs or brain it could be fatal.
The research will determine the frequency of venous thrombosis, the magnitude of its association with air travel and the possible causal mechanisms involved, WHO said in the statement.
If a significant association is discerned, these studies will also provide clues on prevention strategies for air travellers, whatever the level of risk they have, it added.
In March, the WHO meeting recommended common sense measures, urging airline passengers to cut alcohol intake, drink adequate fluids, wear loose clothing and do exercises while seated.
WHO said current studies were myriad, uncoordinated, and small-scale, making it difficult to draw solid conclusions.
Dr Derek Yach, a South African doctor who is executive director of WHO's noncommunicable diseases and mental health department, said: Lately, increased reports of cases of venous thrombosis following flights point to the importance of conducting our research without delay.