A British expert noted that business travelers, frequent fliers and people in similar time disruption situations such as shift workers should not panic, however. The human body has a physiological reaction called the circadian rhythm, which is the natural cycle of light and dark, but the effects of changing this rhythm are not yet fully understood.
The University of Virginia research team compared how old and young mice were affected by this circadian rhythm, as frequent changes between "light" and "dark" were observed.
One test involved a group of mice whose "internal clocks" were shifted forward by six hours, once a week. This subjected the mice to less time in the dark. Another group of mice experienced a six-hour backward shift, which gave them more time in the dark. Yet other groups of older and younger mice experienced normal sleep cycles as control groups.
The young mice in which sleep schedules were shifted forward or backward appeared unaffected by alterations to their schedule. However, only 47 percent of the older mice who experienced less of the "dark" survived, while 68 percent of those with more "dark" time saw lengthened survival times -- both compared to 83 percent of those mice who remained on a normal schedule.
The researchers who published the study indicated that the cause of increased mortality in the mice could be linked to sleep deprivation or immune-system disruption. In addition, suggestions that the interruption of the circadian rhythm were put forward as possible reasons, along with the general frailty of the elderly mice as possibly being more affected by the light cycle changes experienced.
Dr. Gene Block, who led the research team, said that "Whatever the precise mechanism, this raises 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."