Even passengers on short flights may be at increased risk of suffering deep vein thrombosis, says a researcher.
Research has linked long-haul flying to DVT
A study of people travelling between Stansted Airport and Italy found that dangerous blood clots could develop in the first few hours of a flight.
The researchers, from G d'Annunzio University in Pescara, discovered new clots in 4.3% of "high risk" flyers.
These clots can kill if they move from the lower legs and lodge in the lungs or brain, say experts.
It is a widely-held belief that only those travelling for more than five hours may have a significantly increased risk of DVT.
Most research has linked longer flights to the condition.
Despite the nickname "economy-class syndrome", DVTs can occur during any lengthy period of immobility, whether it be in a car, train or plane - or simply sitting at a desk.
The Stansted study found that blood clots could arise
in the first two to three hours of a flight, confirming fears that short flights could be as dangerous as long-haul travel.
The interim results of the latest research, which has so far involved ultrasound tests on 568 passengers before and after they travelled.
High risk flyers
The passengers were aged between 25 and 65, and were screened for extra risk factors which might make them prone to DVT.
These include preexisting health problems such as heart disease, people who have just had operations, and women who are pregnant, taking the Pill or HRT.
Drinking alcohol prior to the trip is also a risk factor, as it dehydrates the body and makes the blood "stickier".
The researchers discovered clots in 4.3% of the high-risk subjects after the
Two passengers actually went on to develop pulmonary embolisms - where the clot moves to the lung - possibly
related to their trip.
Professor Gianni Belcaro, who led the study, said: "The results show passengers are at risk of developing
blood clots even on short flights.
"In fact, our research suggests most blood clots develop in the first two to
three hours of a journey and grow larger and more dangerous with time.
"The problem can be worsened if travellers are then transferring straight to
a car or coach for a long journey, or if they wait hours in airports."
Professor Belcaro said that passengers embarking on short or long-haul flights should drink plenty of water, try to exercise their legs during the flight at regular intervals, and refrain from drinking alcohol or coffee.