But the bulk of any protection may depend on you, the passenger. If you have a chronic health problem, the Lancet authors suggest a preflight medical assessment to determine whether it is safe for you to fly and what precautions you should take if you do fly.
Airline cabins are commonly pressurized to altitudes of 1,524m to 2,438m above sea level. Healthy people have no problem at such altitudes, but those with underlying heart or respiratory disease who may already have low levels of oxygen in their blood can develop symptoms of mountain sickness — fatigue, headache, light-headedness and nausea. Those passengers may need supplementary oxygen when flying, the doctors wrote.
Even healthy passengers may develop mild abdominal cramps and ear problems as gas in body cavities expands with rising altitudes. The doctors warned against flying too soon after surgery, and they cautioned scuba divers against flying within 12 hours of a dive (24 hours for those who do several dives a day), lest they develop decompression sickness.
The risk of blood clots starts to rise four hours into a flight and peaks on flights of more than eight hours. Flying business class offers no protection, despite the expanded leg room, research has shown. The more flights taken within two weeks, the greater the risk. Passengers who are obese, have cancer, recently had surgery, take oral contraceptives or have conditions that raise their susceptibility to blood clots (including genetic conditions like factor V Leiden) are at particular risk of flight-induced clots. Many may benefit from blood thinners when flying.
On long flights, the less that passengers move about the cabin and the less water they consume, the greater the risk. Wearing compression stockings and exercising the calf muscle during the flight can lower the risk.
While exposure to cosmic radiation is not considered a problem even for frequent air travelers unless they are pregnant, anyone can develop jet lag from abrupt changes in multiple time zones. After a westward flight, it can take a day to adjust for every time zone crossed; after an eastward flight, a day and a half.
Although controlling exposure to sunlight is the best way to limit jet lag, it can be challenging for some travelers, so the doctors recommend taking melatonin (0.5 to 5 milligrams). When flying eastward, try to get morning light (wear sunglasses only in the afternoon) and take melatonin at the desired bedtime. When flying westward, get afternoon light (wear sunglasses only in the morning) and take melatonin in the morning. And in either direction, be sure to stay well hydrated.
To prevent contagious illnesses, the most important measure is to be sure all your immunizations are up to date, including annual flu shots. The Lancet authors noted that the “risk of onboard transmission of infection is mainly restricted to individuals with either close personal contact or seated within two rows” of an infected passenger.
But since there may be no way to know who sitting near you might be infectious, my regimen should not hurt and may very well protect you.
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