The potentially unfriendly skies


November 19, 2019 – For elderly and unhealthy people, air travel—particularly long flights—may pose more serious health risks than previously thought, says Eileen McNeely, an instructor in the Harvard T.H. Chan School of Public Health Department of Environmental Health and director of the Sustainability and Health Initiative for NetPositive Enterprise (SHINE), the School’s corporate health and sustainability program.

Q: Your most recent study looked at how flying affects the health of elderly individuals and those with preexisting cardiovascular disease. What prompted you to conduct this study, and what did you discover?

A: In previous research, we conducted hyperbaric chamber experiments that created simulated flight conditions, which enabled us to learn more about how the cabin environment influences both older people and those with chronic conditions. We found that, during flight, older and vulnerable passengers experience moderate hypoxia—a lack of adequate oxygen supply. That finding made us wonder what type of stress this suggested for the heart. In our recent study, we evaluated cardiac responses, and found that, even with air pressurization at the equivalent of 7,000 feet altitude—which is lower than the typical 8,000 feet—flying may pose more cardiovascular risk than previously understood. Among older and vulnerable passengers, heart rates went up and heart-rate variability went down—both indicators of cardiac stress.

Planes typically fly at about 35,000 feet above sea level, which helps them fly faster and more efficiently because the thinner air at that level means the plane faces less resistance. But flying that high means the cabin has to be pressurized so that passengers and crew don’t experience negative health impacts. Everyone thinks the cabin is pressurized at ground level, but it’s not. It’s maintained at the equivalent of 8,000 feet above sea level, which is assumed to be safe based largely on research done in the World War II era, when most of those flying were healthy young male fighter pilots. Eight thousand feet was just below the level—10,000 feet—at which cognitive changes from hypoxia were evident. According to FAA regulations, pilots must don oxygen masks at 10,000 feet or equivalent cabin pressure.

Today, the population of air travelers has changed. More and more people are traveling when they retire, and close to 70% of people over age 60 have some sort of cardiovascular disease. And when you put them at 8,000 feet cabin pressure, it is quite challenging for their health, especially when they live at sea level.

Add to that the fact that, by the time people get inside the airplane they are probably very stressed, because they’ve gone through TSA checkpoints, they’ve maybe walked a good distance to get to the airport gate, they might not have had enough sleep or enough hydration, and their heart could be pumping hard. And the plane’s ascent to the cruising level of 35,000 feet happens really fast—in about 15 minutes. On the flight, people often take medications that knock them out, or they drink alcohol. Those are actually the worst things you can do, because they add physiological stress. Some medications, for example, may lower breathing rates in an already low-oxygen environment. Other medications, if they cause sedation and reduce the chance that people will move around, may put people at risk for deep vein thrombosis (DVT). Although the risk for DVT in flight is very low, lack of mobility complicates it.

Alcohol can sedate people too, and it also increases dehydration. Besides having low oxygen levels, the aircraft cabin is very dry, so people should be drinking lots of water instead of alcohol.

It’s not just passengers who should think about the health risks of flying, but also crews. They’re pushing meal carts on intercontinental long-haul flights, which is like lifting weights. Just as passengers are aging, so are crews.

Q: Do your findings mean that people should be concerned about having a heart attack during flights?

A: While numbers have been rising, heart attacks in flight are still rare events. But we don’t know what a person’s risk is during the 72 hours following the stress of air travel. We did do one study with a group of German airline passengers and found an association between flying and increased risk of heart attack up to 72 hours after they flew. People go home and may have health issues, but we don’t necessarily associate it with flight-related stress. One way we are considering monitoring the post-flight health of passengers is by working with car rental companies that cater to transcontinental flyers, to see their accident rates.

If you’re flying for a couple of hours, the risks are probably not very high. But what we do see, and what was evident in this study and in others, is that the longer you are aboard, the more severe the risk. A tipping point is after about three-and-a-half or four hours. One limitation of our new study is that we looked only at four-and-a-half- to five-hour flight simulations. Many flights are much longer and could potentially pose greater risk. We need more research to fully understand these risks.

Q: What steps are airline companies taking to mitigate the health risks of flying? What can people do for themselves?

Airline companies are thinking about this issue. Qantas Airlines, for example, is planning to begin ultralong flights of 19 or 20 hours, and it’s doing studies to see how people will fare. They plan to use new aircraft that have been redesigned with the cabin pressure equivalent to 6,000 feet and with lighting that will take into account people’s circadian rhythm, so that they don’t leave the plane totally exhausted. Qantas is also looking at how to mitigate the effect of lengthy exposure to noise. Other airlines are thinking about ergonomics, food, and hydration.

Passengers can track what is happening to them during flights using wearable technologies, so they can get an idea of how long flights are affecting their heart rate or oxygen level. If they have concerns they can check with their doctors, although my experience is that many providers may not fully understand the conditions in flight. Some education is needed all around—and ideally before a long flight.

We’ve developed an app called FlightHealth that’s geared to airline crews, to help them monitor their inflight health. Anyone can download the app, but we also plan to create a passenger-oriented version in the future.

Karen Feldscher