A new study on mice has shown that chronic jet-lag like conditions may hasten death in old age.
Led by Gene Block and Alec Davidson of the University of Virginia, a team of researchers put aged mice into weekly light-cycle shifts, similar to those that humans experience with jet lag or rotating shift work.
The found that those mice experienced significantly higher death rates than did old mice kept on a normal daylight schedule over the same eight-week period.
The study shows gives a new insight into how the disruption of circadian rhythms can impact well-being and physiology, and how those impacts might change with age.
In a previous study the researchers had seen that a surprising fraction of aged genetically altered rats, which were exposed to a six-hour advance in their light cycle, had died after the shift in schedule.
In the new study published in the journal Current Biology, they examined the mortality link in earnest by looking at how young and old mice fared when subjected to two different types of light-cycle shifts.
In one regimen, mice experienced a six-hour forward shift once a week, while in the other, they experienced a six-hour backward shift. A “control” group of young and old mice did not experience any schedule shifts.
The researchers noticed that the young mice generally survived well under the various conditions, whereas the light-cycle shifts had a marked effect on the survivorship of the old mice.
While 83% of old mice survived under the normal schedule, 68% survived under the backward-shift regimen, and 47% survived under the forward-shift regimen.
Previous studies had helped establish links between changes in light schedule and death in other animals and under different experimental circumstances. But the new findings indicate that there may be a differential effect of mortality depending on the direction of the schedule shift – forward or backward.
The researchers noted that chronic stress, as measured by daily corticosterone levels, did not increase in the old mice experiencing the light-cycle shifts.
They say that the underlying cause of the increased mortality is not yet clear, but it could involve sleep deprivation or immune-system disruption.
Researches conducted in the past have shown that circadian clocks govern physiological rhythms in a great variety of tissues in the body, and that different aspects of the physiological clock can adjust to schedule changes at different rates.
The researchers now speculate that the internal lack of synchrony among different physiological oscillations may have serious health consequences that are exacerbated in aged animals.