From the Washington Post.
VITAL EVIDENCE
When the Clock Lies
Tuesday, November 7, 2006; Page A02
People who regularly experience jet lag, or who alternate working day and night shifts, may face greater risks than they know.
Researchers at the University of Virginia came to this conclusion based on experiments they did with mice whose waking and sleep hours were repeatedly shifted either forward or back by six hours. While younger mice were apparently not harmed, older mice were hit hard by the time changes, especially when their "daylight" was being shifted six hours earlier -- comparable to the time shift that travelers flying from the United States to Europe experience.
Among the older mice whose light cycle was shifted six hours earlier, 53 percent died over the eight weeks of the experiment. Among those whose light cycle was shifted back, 32 percent died. Only 17 percent died among the mice who had no shifts at all. When the frequency of the shifts was increased, the number of mice that died increased as well.
The team, led by biologist Gene Block, initially thought that chronic stress caused by the day-night changes could be causing the deaths, but they found that daily levels of corticosterone -- a hormone released at times of stress -- remained constant. As a result, they hypothesized that forced changes in the circadian rhythms of day and night led to sleep deprivation and suppression of the immune system, which in turn undermined the health of the mice.
Previous experiments have shown that nearly all tissues and organs have circadian rhythms, which adapt to change at different rates. The time-shifted mice may have died, the authors speculate, because their various internal clocks got seriously out of sync.
The study, in the journal Current Biology, concludes that the findings "raise important issues about the safety of counter-clockwise rotating shift work and the potential long-term health consequences for airline crews regularly crossing time zones."
-- Marc Kaufman
VITAL EVIDENCE
When the Clock Lies
Tuesday, November 7, 2006; Page A02
People who regularly experience jet lag, or who alternate working day and night shifts, may face greater risks than they know.
Researchers at the University of Virginia came to this conclusion based on experiments they did with mice whose waking and sleep hours were repeatedly shifted either forward or back by six hours. While younger mice were apparently not harmed, older mice were hit hard by the time changes, especially when their "daylight" was being shifted six hours earlier -- comparable to the time shift that travelers flying from the United States to Europe experience.
Among the older mice whose light cycle was shifted six hours earlier, 53 percent died over the eight weeks of the experiment. Among those whose light cycle was shifted back, 32 percent died. Only 17 percent died among the mice who had no shifts at all. When the frequency of the shifts was increased, the number of mice that died increased as well.
The team, led by biologist Gene Block, initially thought that chronic stress caused by the day-night changes could be causing the deaths, but they found that daily levels of corticosterone -- a hormone released at times of stress -- remained constant. As a result, they hypothesized that forced changes in the circadian rhythms of day and night led to sleep deprivation and suppression of the immune system, which in turn undermined the health of the mice.
Previous experiments have shown that nearly all tissues and organs have circadian rhythms, which adapt to change at different rates. The time-shifted mice may have died, the authors speculate, because their various internal clocks got seriously out of sync.
The study, in the journal Current Biology, concludes that the findings "raise important issues about the safety of counter-clockwise rotating shift work and the potential long-term health consequences for airline crews regularly crossing time zones."
-- Marc Kaufman
TC
