Nov. 6, 2006 - Jet lag and shift work may be more dangerous than peoplethink, animal studies suggest.
University of Virginia researchers report that a six-hour shift in timeschedule once a week, for up to eight weeks, hastens death in elderly mice. Thetime shift is generally not fatal for young animals.
Also, advancing the mice's schedules was more lethal than delaying them, sayAlex J. Davidson, PhD, Gene D. Block, PhD, and colleagues in an article in theNov. 7 issue of Current Biology.
In the study, 53% of elderly mice put on an advanced-time schedule were deadafter eight weeks, compared with only 17% of the elderly mice on a normalschedule.
"The dramatic differences in morbidity associated with phase advances ofthe biological clock raise important issues about the safety of ... rotatingshift work and the potential long-term health consequences for airline crewsregularly crossing time zones," Davidson and colleagues conclude.
The researchers didn't start out studying jet lag. They were working on adifferent study when they noticed older mice tended to die when their timeschedules were advanced.
Davidson and colleagues took groups of young and old mice and shifted theirtime zones once a week. One group had their schedules advanced by six hours,while another had their schedules delayed by six hours. A third group stayed ontheir normal time.
Eight weeks later, there was no difference among the young mice.
But for elderly mice, the difference was remarkable. Only 17% of thenormal-time mice had died. But 32% of the delayed-schedule mice were dead, anda whopping 53% of the advanced-schedule mice had expired.
Stress did not seem to be a factor, as the deadanimals did not have high levels of stress-related hormones.
Exactly what did kill the mice isn't clear. Davidson and colleagues saysleep deprivation or disruption of the immune system may have been toblame.
Whatever the reason, the researchers say upsetting the internal time clockcan have serious health consequences -- and these consequences may be far worsefor those getting on in years.
Davidson is currently with Morehouse School of Medicine in Atlanta.