New Delhi. Long distance travelers periodically should move around and stretch their legs, and drink plenty of water to stay hydrated, said Dr KK Aggarwal, President Heart Care Foundation of India & MTNL Perfect Health Mela.

Long–distance travel can lead to potentially fatal blood clots in some people –– showing that the risk grows with the length of the trip. Certain people are at increased risk of blood clots, including cancer patients, people who have recently had major surgery such as a joint replacement, and women on birth control pills.

In general, travel is associated with a nearly three-fold increase in the risk of venous thromboembolism (blood clots that form in the veins), often in the legs. If such a clot dislodges and travels to the lungs, it can cause a potentially fatal condition called pulmonary embolism.

A combination of factors including dehydration and hours of sitting in cramped conditions explains why some people develop blood clots. A review, published in the Annals of Internal Medicine, analyzed 14 studies involving more than 4,000 cases of venous thromboembolism and found that travelers had a nearly three–fold higher risk of blood clots than non–travelers. The risk climbed along with the duration of the trip –– rising 18 percent for every two hours of any type of travel, and by 26 percent for every two hours of air travel.

But there is no reason for panic, because the absolute risk to any one traveler is still low. People who travel long distances should be aware of the risk of blood clots and learn to recognize the symptoms. Symptoms of a blood clot in the leg include pain, warmth, swelling and redness in the limb. If the clot travels to the lungs, it may cause sudden shortness of breath, chest pain or a cough that produces blood.