CBS News medical correspondent Dr. Jennifer Ashton shared the findings on "The Early Show" and discussed how to avoid developing deep vein blood clots.
Blood clots, known as deep vein thrombosis (DVT) or venous thromboembolism (VTE), form most often in the leg, Ashton explained. Sometimes, she said, the clot breaks off and travels to the lung and may cause an embolism that can result in death. Sitting for long periods of time, whether in a plane or car, Ashton said, decreases the blood flow in the legs, causing clotting.
Ashton said it's common for blood clots to occur with no symptoms. In fact, she said, in about half of all cases, there are no noticeable symptoms.
However, when signs and symptoms of blood clots do occur, they can include:
-Swelling in the affected legs; this can include swelling in your ankles and feet.
-Pain in your legs; this can include pain in your ankles and feet. This pain often starts in your calf and can feel like cramping or a "charley horse."
-Redness and warmth over the affected area.
-Pain or swelling in your arms or neck. This can occur if a blood clot forms in your arms or neck.
Ashton added some people are more prone to developing clots than others, such as people who smoke, have cancer, take hormones, are obese, have high cholesterol or high blood pressure, and have a family history of clots.
But what type of travel is more of a blood clot risk?
Ashton said any type of travel where you are immobilized is a risk for blood clots, but with air travel, the risk goes up with every two hours of the flight.
"With millions and millions of people traveling, this is a real significant health issue," she said.
As for reducing your chances of getting clots on a long trip, Ashton suggests wearing compression knee-highs (available in drugs stores or surgical supply stores), drink water (because dehydration increases risk) and get up every hour to walk around and stretch (gets the blood circulating).
If you are not sleeping or are on hormones, Ashton said, this can slightly increase your risk of clot formation.
For more information, visit the National Heart, Lung, and Blood Institute.