The American Physical Therapy Association has issued advice to vacationers concerned by the risk of deep vein thrombosis (DVT) when flying.

Citing a number of key studies into DVT since the 1950s - when the disorder was first recognized - research by the association dispels most health concerns for those under 40 and offers advice to those who suspect they are at risk.

Recent investigations have suggested that long-haul flights only minimally increase the danger of developing a blood clot within two weeks in most people, but certain individuals are more at risk than others.

Those with a family history of blood clotting, or with certain blood diseases, can be at greater risk; as can new mothers, pregnant women, or those on hormone replacement therapy.

Patients undergoing treatment for circulation problems, or recovering from recent surgery to their hips or knees should also take heed of the following steps - devised by the Cedars Sinai Medical Center - to reduce the threat of DVT.

“As physical therapists and experts in movement, we have been able to guide and provide movement interventions and exercises as prophylactic measures in prevention of this potentially killer condition,” said the center’s Zahra Ghasemi.

Wearing loose clothing, drinking plenty of water, walking at every opportunity and avoiding excessive alcohol are said to be the key steps to preventing the onset of DVT while flying.

Vacationers are also advised that crossing your legs can compress the blood vessels and encourage symptoms.

All fliers should also be sure to invest in suitable travel insurance before taking to the skies.