According to a recent study, mice die early when exposed to time shifts simulating the effects of jet lag. This proposes working unusual shifts and flying across time zones could affect health.
'While there's no indication that older humans shorten their lives by flying across time zones or doing shift work, the research does suggest there might be a potential problems,' said study co-author Gene Block, a professor of biology at the University of Virginia.
'Most people report it's more difficult to cross time zones as they age,' he said. 'But whether it's really deleterious or not, we don't know yet. And we don't know if there is cumulative damage, whether those exposures create problems later on in life.'
The study was published in the Nov. 7 issue of the journal Current Biology. Gene Block and coworker Alec Davidson said they stumbled onto the findings accidentally. In a different study, genetically engineered mice died when they were put under lights 6 hours before usual, however, no deaths were observed when the light schedule was delayed.
Based on this, they conducted a study on 3 groups of mice, each group comprising 30 old mice and 9 young mice.
In the first group, the light/dark cycle was advanced by 6 hours, simulating people getting up 6 hours early, each week for 8 weeks. While in the second group it was delayed steadily by 6 hours. The light/dark cycle was not changed for the last group.
The results revealed that only 47% of the old mice survived in the first group, when compared to 68% of the old mice in the second group and 83% in the third group.
The number of deaths increased when the light was altered more frequently, i.e., every 4 days. There was no change in the stress level as no increase in the stress hormone, corticosterone, was noticed.
'Alternatively, the general frailty of older animals rather than age-related changes in the circadian system may make them less able to tolerate changes in the light schedule,' the researchers wrote.
Dr. Bob Vorona, a sleep specialist and associate professor at Eastern Virginia Medical School who's familiar with the study findings, said, 'There are some signs that changes in light schedules can harm humans, too.
'Shift work has been associated with higher rates of breast cancer and heart problems,' he said.