The low pressure and low oxygen environment on flights they say may add to the risk of thrombosis, which is increased between 2 to 4 times after air travel, especially long flights.
The exact reasons are unclear but the scientists think although immobilisation for long periods could play a part, other flight-specific factors may also contribute.
Frits Rosendaal and a team from Leiden University Medical Centre, Netherlands, measured the concentrations of markers of clotting activation in blood samples in 71 healthy volunteers (15 men and 56 women), during an 8-hour flight, 8 hours at a cinema, and 8 hours of normal activity.
Measurements were tested in blood samples before, during, and after each situation.
They found increased concentrations during the flight but not in the other two situations.
Concentrations were found to be higher in the 40 per cent of volunteers with other thrombosis risk factors - a mutation in the factor V gene and those on oral contraceptives.
Professor Rosendaal concludes that "Activation of coagulation [clotting] occurs in some individuals after an 8 hour flight, indicating an additional mechanism to immobilisation underlying air travel related thrombosis."
However other experts insist that prolonged immobilisation in a sitting position plays an important role in provoking thrombosis and this applies to trips by train or car as well.
They continue to recommend exercising during flights, wearing compression stockings, and avoiding excess alcohol and sedatives.
The research is published in the current issue of The Lancet.
This is the first time experimental data have successfully provided a mechanistic explanation for how interaction between genes can affect how populations are altered by natural or artificial selection.
"The results are not surprising, since it has long been suspected that interaction is important in the regulation of most biological traits, but this type of mechanism was not expected to play such a dominant role", says Orjan Carlborg.
The two poultry lines differ also in regard to other features than growth, such as appetite, obesity, and immune response. The high-line chickens are compulsive eaters, whereas the low-line chickens are anorectic; the high-line chickens are fat while the low-line chickens are slender; and the high line also has a weaker immune response than the low line.
"This is why we expect that this animal model will be extremely interesting for finding out whether the mechanism we have discovered might also underlie the regulation of the medically interesting metabolic and immmunological traits, including regulation of appetite, obesity, and immune response. This can provide new knowledge that may ultimately lead to improved drugs for many of our complex diseases", says Orjan Carlborg.
The authors are Orjan Carlborg, Lina Jacobsson, Per Ahgren, Paul Siegel, and Leif Andersson.
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