Aging in the Air

Everyone who has spent an eternity or two trapped in a plane waiting for flight clearance knows deep in his or her bones that modern air travel makes us old before our time. But could there be more to that feeling than mere ennui?

With that question in mind, I read with interest “Do Frequent Fliers Age More Slowly?” by Valerie Ross, one of my journalism grad students in the Science, Health and Environmental Reporting Program at New York University. By all means, do read her entertaining discussion of the problem, but here’s the gist of it:

Air travelers are subject to two different relativistic effects that should influence how rapidly time passes for them. On the one hand, because fliers are moving with respect to us on the ground, special relativity dictates that they must experience some degree of time dilation: they ought to age ever so slightly less rapidly than we on the ground do. But on the other hand, because they are also a few miles higher than us in Earth’s gravity well, general relativity says that time for them should pass a bit more quickly, because time also dilates with the intensity of the gravitational field. Each of those effects—one stretching time, the other compressing it—is infinitesimal under these conditions because there is simply not enough difference in velocity or gravity for much dilation to occur but it should occur nonetheless. Do those effects simply cancel each other out or does one slightly predominate?

The answer, according to physicist Chin-Wen Chou and his National Institute of Standards and Technology colleagues, is that on average altitude overpowers velocity, and fliers should age ever so trivially more quickly than those of us on the ground. How much more? As Valerie writes:

The difference is so small, however, that even the most tireless jet setters don’t have to worry about extra wrinkles. Consider an extreme case of the commercial air passenger: Ryan Bingham, the constantly traveling businessman played by George Clooney in “Up in the Air.” By the time Bingham racked up those 10 million frequent flier miles, Chou calculated, he’d aged only 59 microseconds more than his colleagues back in Omaha.

So much for what physics says about airflight-induced decrepitude. But wait! What might biology tell us about this situation?

Remember, because air travelers are at altitude, they are typically exposed to slightly higher levels of ionizing cosmic rays. (Consider these estimated exposures for passengers and flight crews on consumer flights, for example.) Ionizing radiation is associated with cancer and other acute health problems because of the damage it does to DNA, but there have also long been concerns that it might cause something like premature aging, if only by inducing various age-related ailments. (NASA has been particularly worried about this phenomenon because astronauts on extended space voyages would probably experience chronic low-level radiation exposure.) Unfortunately, not much is yet clearly known in detail about low-level radiation and its influence on aging, so meaningfully calibrating any effect currently seems to be out of the question. I would hazard to guess, though, that if the radiation effect exists, it far exceeds the vanishingly small relativistic effect from altitude.

But wait! Can we grasp at straws and hope that the effect of the radiation wouldn’t be entirely bad? Might the radiation have any rejuvenating influence that could offset any of the radiation damage and the time-compressing physics?

That possibility speaks to the idea of hormesis: the theory that low levels of toxins or radiation might stimulate the body’s regenerative mechanisms enough to have net healthful effects. Hormesis is, to say the least, a controversial notion, though it seems to be somewhat better regarded in part of Europe than in the U.S., much like homeopathy, the quacktacular pseudomedicine that relies on a similar “dose makes the poison” philosophy. For example, the 2006 research review Health Risks from Exposure to Low Levels of Ionizing Radiation: BEIR VII Phase 2 by the National Research Council’s Committee to Assess Health Risks from Exposure to Low Levels of Ionizing Radiation concluded:

The committee concludes that the assumption that any stimulatory hormetic effects from low doses of ionizing radiation will have a significant health benefit to humans that exceeds potential detrimental effects from the radiation exposure is unwarranted at this time.

However, even if we extend hormesis the benefit of the doubt, whatever would  constitute a “healthy,” anti-aging dose of radiation would depend hugely on individual factors: body size, state of health, personal genetics, exposure to other toxins and so on, not to mention details about the flight itself (duration, latitude, altitude, etc.). As such, it seems vastly more likely that the haphazard radiation exposure passengers on a plane would receive would be far more likely to do harm than to help. But whether that damage would equate to additional aging is itself very much up in the air.

So in short, we can only say two things. First, air travel is most likely only going to make you older (but cheer up: probably not enough to matter). And second, the years you spend at the baggage carousel waiting for your luggage to arrive are gone forever.

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