Danger in the Window Seat

By Sanjay Gupta

I travel a lot -- more than 20 countries last year alone--and that means a lot of time on airplanes. I always worry, because there's a good chance that when I land I'll have the sniffles or something worse. When I started looking into the health risks of air travel, I discovered that a lot of people--as many as 70% of travelers--are just like me. They disembark complaining of everything from earaches and motion sickness to viral infections and dehydration made more severe by the dry air that circulates in airplane cabins.

But the most serious risk to air travel is a condition known as DVT, or deep-vein thrombosis. DVT is caused by blood clots that form in the legs, pelvis or arms. The clots usually aren't dangerous, but if they break off and lodge in the tiny vessels that feed the lungs or heart, they can be fatal.

Because DVT is associated with cramped airline seats, it came to be known as economy-class syndrome. (Former Vice President Al Gore, however, developed DVT in aircraft with plenty of leg room while he was campaigning for the presidency.) Many doctors suspected that the clots might be caused by low air pressure or changes in oxygen concentration during flight, in part because mountain climbers are known to develop DVT at high altitudes. But no one knew for sure.

That's why a DVT study published last week in the Journal of the American Medical Association caused such a stir. Scientists in Scotland asked 73 healthy volunteers to spend eight hours in a hypobaric chamber in conditions that simulated a plane flying at nearly 8,000 ft. Blood drawn after the test showed no evidence that air- pressure or oxygen levels had activated the clotting mechanism.

Instead, the biggest risk factor for DVT seems to be how much time you spend in an airplane seat. An earlier study of more than 135 million passengers found that those who traveled more than 3,100 miles in one trip were 150 times as likely to develop clots. That can happen on the ground too. David Bloom, an NBC war correspondent, died in 2003 after developing DVT while reporting in Iraq. It was believed to have been caused by dehydration (which thickens the blood) and the cramped condition of the armored vehicle he traveled in.

Research indicates that the vast majority of people who develop DVT, on or off a plane, have at least one other risk factor, such as cancer, circulation problems, a family history of thrombosis or a bad knee or hip. Pregnant women or women on birth control pills are also at higher risk.

It's a lot to think about while you're waiting at the boarding gate. But there are ways to lower your risk: stay hydrated (by drinking plenty of water and laying off alcohol and caffeine), move around as much as possible, avoid sleeping pills that knock you out, consider wearing support hose to improve circulation, and ask your doctor about taking aspirin to thin your blood.

You'll still be at risk for getting the sniffles, but I'll tackle that in another column.

Sources: CNNMoney.com U.S. Bureau of Transportation

Sanjay Gupta is a neurosurgeon and CNN medical correspondent