It seems that there's another reason to fear flying. Scientists say that frequent air travel is directly linked to flu outbreaks.

A new study shows a direct correlation between air travel and the spread of the flu. Harvard health experts tracked flu and travel data from 1996 to 2005. After the Sept. 11, 2001 attacks, U.S. air travel fell by 20 percent during the fall months. That year, our normally predictable flu season was delayed by about two weeks, according to health researchers.

U.S. flight data during the month of September enables them to predict when the flu season will peak. Data from November informs them about how quickly it will spread. And, as most of us suspected, frequent air travel speeds the spread of the flu.

Still, their study focused on how and when the flu virus spreads. What I wonder about is whether sitting on a plane for several hours makes you sick. Travelers have long speculated that being on a flight for several hours leads to colds, bugs and the flu. Airlines (and perhaps health experts) deny any direct correlation. But time after time, I've noticed that I'm likely to catch a bug after a long flight.

I don't know if it's the cramped airline seats, contact with a broad swath of humanity, jet lag, poor air filters on the plane or just a coincidence. But after a long flight, I'm much more likely to pick up a bug.

I'm not the only one. CNN put together this list of tips to prevent illness during long flights. (Wash your hands, drink fluids, consume vitamin-rich foods).

Last spring, the New York Times interviewed jet setters to hear which talismans they use to ward off illness. Some assemble "cleanliness kits" with immune-boosting pills, disinfectant wipes and antibacterial hand lotion. Others drink lots of water and walk frequently to prevent blood clots in their legs. I swear by Airborne, and throw a vial in my carry-on as travel insurance. It works for me; I don't know how or why.

In any case, it's clear that racking up lots of frequent flyer miles is somewhat hazardous to your health. But I'd be willing to risk it for a trip to Hawaii.