By Randy Dotinga, HealthDay via Gannet News Service
If flying to London throws off your body clock for a few days, be happy you're not a rodent. According to a new study, elderly mice die earlier if they're exposed to time shifts that replicate the effects of jet lag.
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."
One thing seems clear: Older mice have a hard time tolerating shifts in patterns of light and dark. In both humans and rodents, light acts to synchronize body clocks and adjust sleeping patterns. Traveling across multiple time zones or changing work shifts can throw off those internal systems, however.
Block and his colleagues were inspired to launch their new study after they noticed that a large number of older rats died after undergoing changes in how they were exposed to light.
In the new study, the researchers experimented on young mice and old mice that were 28 to 32 months old, the rough equivalent of a human who's between 70 and 90. Through changes in light, the time clocks of one group of mice were shifted ahead six hours once a week — the equivalent of flying from the East Coast of the United States to Europe. Essentially, morning and night came six hours later for the mice.
Other mice were shifted backward by six hours once a week, while another group didn't undergo any time shift at all.
Nearly all the young animals "did fine" and survived the time shifts, Block said. And 83% of the old mice survived under the unchanged schedule.
But only 47% of the old mice survived the forward time shift, and 68% survived the backward time shift.
"It appears that eastward adjustments are more difficult — advances are more difficult than delays," Block said.
The results are in the Nov. 7 issue of the journal Current Biology.
In searching to explain the findings, the researchers at first thought the older mice were simply stressed out, but tests suggested that wasn't the case.
One possibility is that the changes in schedule deprived the mice of sleep, Block said. "Another possibility would be that the immune system can be compromised in animals with altered light schedules," he said.
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.
According to Vorona, shift work has been associated with higher rates of breast cancer and heart problems. One Israeli study even showed a higher rate of mental problems in tourists who traveled through multiple time zones.
For now, Block isn't recommending that anyone stop traveling. But, the findings should make people more alert to "the fact that time-zone changes can be stressful" and require proper rest and recovery, he said.