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Are there any health risks from flying all the time — like radiation?

We tend to think of the "hypermobile" as being ultra-glamorous global elites who practically live on planes, toting their Tumi bags and Monocle magazines with them as they jet off to one new foreign locale after another. What's more luxurious than breakfast in New York and dinner in Rome?

The evidence, however, tells a different story. The world's most frequent fliers — diplomats, aircrew, and international business folks — are increasingly being seen as shift workers whose lifestyles pose serious health risks.

Anytime you fly 30,000 feet in the air from one continent to another, you're exposing yourself to a small amount of cosmic radiation and jet lag. If you only fly a couple of times a year, this isn't really anything to worry about. The amount of radiation is minuscule, and jet lag can usually be overcome in a few days.

But for anyone flying dozens of times per year — say, at least two cross-country flights per month — these stresses start to add up, putting frequent fliers in higher risk categories for cancers and other chronic health issues.

"Some frequent fliers would be surprised to learn that their exposure to radiation exceeds that of nuclear power workers," said the University of Surrey's Scott Cohen, who has studied the dark side of hypermobility. "And few would realize that frequent jet lag disrupts genes that influence aging and heightens the risk of having a heart attack."

In short, there are real — and still underappreciated — health risks associated with globetrotting.

The radiation risks of air travel are small — but add up for very frequent fliers

The sun and stars are constantly bombarding Earth with cosmic radiation. Normally, our planet's atmosphere and magnetic field protect us from most of those particles. But if you're 30,000 feet up in the air, the atmosphere is thinner and exposure is ever so slightly higher.

This is nothing to worry about if you're flying occasionally. The chart below shows how much radiation you'd get on a flight from New York to Los Angeles. I asked two epidemiologists with the Centers for Disease Control and Prevention, Lynne Pinkerton and Barbara Grajewski, about folks who take sporadic flights, and they said there's no cause for concern.

But here's the twist. If you start flying constantly, those tiny doses of radiation can start to add up. Both Pinkerton and Grajewski pointed out that in some countries, flight attendants, pilots, and other aircrew are actually considered radiation workers — because they're being exposed to as much radiation as some nuclear power plant workers. (Strangely, aircrew are not classified as such in the United States.)

"Some frequent fliers may also be exposed to levels of cosmic radiation similar to aircrew," the epidemiologists added. "These workers need to be informed about their workplace exposures, including cosmic radiation."

Let's quantify this: The International Commission on Radiological Protection recommends dose limits of 20,000 microsieverts per year, averaged over five years (so 100,000 microsieverts in five years) for radiation workers, and 1,000 microsieverts per year for the general public.

As our chart shows, you get about 40 microsieverts of radiation on a flight from Los Angeles to New York, so you'd need to hop on about 25 such flights a year to hit the limit for the public. (By the way, there's no need to worry about airport screening — as you can see on our graphic, it's super minimal. Even the health risk for frequent fliers is considered very small.)

Does this extra dose of radiation matter for health? That's what scientists are still trying to figure out. Research has found that aircrew are more likely to be diagnosed with melanoma (a deadly form of skin cancer) than the general population. In one study, pilots who flew for about an hour at 30,000 feet got the same amount of cancer-causing UVA radiation as that emitted during a 20-minute tanning bed session.

A number of studies have also found that women flight attendants are more likely to be diagnosed with breast cancer than the general population.

Still, with both kinds of cancer, it's difficult to untangle whether it's the radiation exposure alone or other factors that may heighten the risk in people. After all, those who fly more frequently also experience more jet lag — and "circadian disruption" does all kinds of bad things to the body, including increasing cancer risk (more on this later). What's more, estimating radiation doses in these studies is rife with uncertainty and potentially confounding factors.

"Regarding breast cancer, differences in reproductive health issues — for example, they have fewer children and later in life — have been considered, and also the shift and night work patterns of aircrew," explained Hajo Zeeb, an epidemiologist at the Leibniz Institute who has studied the health of flight crew members. For melanoma, there's some discussion that frequent fliers may spend their leisure time differently than others, perhaps in more sunlight, which could account for the difference in melanoma risk. Researchers are still trying to unpack and understand all these factors.

Chronic jet lag is also dangerous

Meanwhile, radiation might not actually be the main thing to worry about. As we learn more and more about how important sleep is for health, we're also learning how much losing sleep and messing up your natural sleep rhythms wreaks havoc on the body.

People who experience chronic jet lag are now seen by researchers as a unique form of shift workers, with long-term health effects. But here, too, there's a big difference between the jet lag occasional travelers face and the chronic jet lag that globetrotters and flight crew experience. It's the latter group that may experience lasting health effects.

Surrey's Cohen said, "The interference with the body’s rhythms reflects a widespread disruption of many biological processes, including gene expression that influences aging." He explained that jet lag can even switch off genes that are linked to the immune system, "raising the risk of having a heart attack or stroke. Long-term chronic jet lag amongst airline cabin crew is associated with cognitive deficits including memory impairment."

"Shift work," said the CDC's Pinkerton and Grajewski, "including the type experienced at work by aircrew, is considered to probably cause cancer in humans by the World Health Organization’s International Agency for Research on Cancer."

Night and shift work has also been linked to miscarriage and reproductive problems. "Miscarriage in the first trimester was 50 percent more likely for a pregnant flight attendant who flew 15 hours or more during her normal sleep hours compared to those who flew less during normal sleep hours," Pinkerton and Grajewski wrote.

But again, occasional or recreational fliers needn't worry. "Most people who board a plane have very little to be concerned about from the exposures we’ve discussed," the researchers said. (And, as a side note, it really does seem melatonin helps alleviate jet lag — see here for details.)

For most flyers, blood clots and getting sick are the big things to worry about

Meanwhile, for most people, the immediate health risks of flying should be considered more than any long-term problems.

These include blood clotting — a risk that increases up to fourfold for long-haul flights. In other words, you don't need to fly a lot to experience this potential health problem. If you're on birth control, that risk can be even higher.

The enclosed spaces in air cabins — combined with your weakened immune system after a bad night of sleep on a long flight — also help to spread infectious diseases. As this overview of health risks and air travel in the Lancet explains, "Since 1946, several outbreaks of serious infectious diseases have been reported aboard commercial airlines, including influenza, measles, severe acute respiratory syndrome (SARS), tuberculosis, food poisoning, viral enteritis, and small pox."

So for most people, radiation exposure and chronic jet leg really aren't worth stressing over. The globetrotters, on the other hand, may want to start rethinking their jet-setting ways.

Send your questions to Julia via the submission form or @juliaoftoronto on Twitter. Read more about Dear Julia here.