Chronic Jet Lag Could Be Bad For Human Health

fromKQED

Jet lag has been linked to a host of health ailments. According to a new study, when the normal sleep rhythms of lab hamsters were disrupted, the animals developed fewer brain cells.

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LINDA WERTHEIMER, Host:

This is MORNING EDITION, from NPR News. I'm Linda Wertheimer.

STEVE INSKEEP, Host:

And I'm Steve Inskeep.

'Tis not the season to be traveling in northern Europe, where travel has been snarled by bad weather all week. Snow and ice have postponed thousands of flights. The hardest-hit airport was London's Heathrow, which was jammed with stranded and, often, angry passengers. Heathrow, at last, is working at nearly full capacity today, but there's such a backlog of passengers, many may still have to wait a couple of days before they make it onto a plane.

WERTHEIMER: When those traveling long distances eventually get to where they're going, they will have another issue to deal with: jet lag. Scientists say it tends to hit women harder than it does men. And it's worse, they say, when you travel east than it is when you travel west. As Amy Standen of KQED reports, jet lag can mean a lot more than just missed sleep.

AMY STANDEN: If you've ever doubted that there is something profoundly unnatural about human air travel, consider the life of a commercial pilot.

PATRICK SMITH: You know, there are certain moments when you're flying, and maybe you see the sunset, you know, twice in a six-hour period.

STANDEN: That's Patrick Smith, a columnist for Salon and host of AskthePilot.com.

SMITH: I recently flew Los Angeles to Taipei, Taiwan, and from the time I arrived in Los Angeles to the time when I landed in Taipei, I think I endured 20-something straight hours of darkness.

STANDEN: Ten years ago, some British scientists did an experiment. It involved two groups of female flight attendants. Both groups flew long distances, changing time zones. But the second group was given a much longer recovery time. Each group took a series of basic memory tests. Lance Kriegsfeld, a professor of neurobiology at the University of California Berkeley, says the second group didn't do so well.

LANCE KRIEGSFELD: They had a grossly reduced reaction time and percent correct on a relatively simple task.

STANDEN: And not just, he said, because they were tired.

KRIEGSFELD: When they scanned their brains, they had smaller temporal lobes.

STANDEN: Yes, a part of their brains was actually smaller. Kriegsfeld was so intrigued by this study that he decided to replicate it, but this time using two groups of hamsters. The first group kept to their regular schedule, lights on and off at the usual times. The second group was jet lagged by six hours, as if, says Kriegsfeld, they had flown from New York to Paris - only instead, they got dissected.

Prof. KRIEGSFELD So in this picture I'm showing you here, there's new neurons being labeled in green and adult neurons that have already been there labeled in red.

STANDEN: In a part of the brain called the hippocampus, a part that is critical for learning and memory, the jet-lagged hamsters had far fewer new brain cells than they should have had.

KRIEGSFELD: Jet lag reduces this by about 50 percent.

STANDEN: Now, humans aren't hamsters, but Kriegsfeld's study supports an idea that scientists have had for some time: that chronic, repeated jet lag may be bad for human health.

Now, to understand why that may be, we go all the way back to 1729, to a very interesting discovery having to do with plants. Charles Czeisler is a sleep expert at Harvard Medical School.

CHARLES CZEISLER: Many people at the time were trying to figure out what the sun did to cause the leaves of certain plants to raise up during the daytime and close down at night. And this astronomer...

STANDEN: A Frenchman named Jean Jacques Ortous de Mairan. He put the plant in a dark closet.

CZEISLER: And lo and behold, the leaves of the plants were open, even though they had not been exposed to the sun that day.

STANDEN: The plants, it turned out, weren't following the sun at all. They were following an internal clock. This is called a circadian rhythm, and we humans have it, too - or rather, the clock, you might say, has us.

KRIEGSFELD: You have daily rhythms in reaction time...

STANDEN: Again, Lance Kriegsfeld from UC Berkeley.

KRIEGSFELD: ...daily rhythms in cognitive function and concentration, daily rhythms in coordination and balance.

STANDEN: Not to mention sleep, digestion. Try doing any of these things at the wrong time of day, and you just won't do them as well. Which brings us back to jet lag and Harvard's Charles Czeisler.

CZEISLER: When we upset the apple cart, it's like an internal temporal chaos, where some of the systems in the body think it's daytime, some think it's nighttime, and they may be working at cross purposes instead of in synchrony with each other.

STANDEN: This phenomenon has been documented not just in pilots and flight attendants, but in people who work the night shift. Studies link those schedules to a host of ailments, including diabetes and digestive problems.

One way that employers could help protect their employees would be to keep them on regular shifts, or change shifts gradually so that the workers have time to adjust. So far, that is a luxury that Patrick Smith, the pilot, rarely gets. He says he knows the risks, but he loves his job.

SMITH: Once upon a time, it took you weeks to cross the ocean in a sailing ship, and now we can do it in a matter of hours, traveling hundreds of miles per hour, you know, above the earth in almost perfect safety, too. It's quite remarkable.

STANDEN: When we fly airplanes, we literally transcend the world we evolved to live in. Smith says that is a trade off he's willing to make.

For NPR News, I'm Amy Standen.

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