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