Jet lag might hasten death in elderly.

When old mice experienced artificial jet lag, their death rate increased, scientists report.

Gene Block of the University of Virginia in Charlottesville and his colleagues study how the body's natural timekeeping, or circadian rhythm, changes with age. Several years ago, the researchers noticed that a surprisingly large fraction of their elderly lab rats died soon after researchers changed the daily cycle of light and dark in rooms containing the animals' cages.

To examine this phenomenon in more detail, Block's team worked with middle-aged and elderly mice. Some of the animals lived in cages where the researchers shifted daytime forward every week by turning the lights on 6 hours earlier, the equivalent of a person flying from the East Coast of the United States to France. The researchers shifted daytime backwards once a week by the same amount for other mice. A third set of mice didn't experience any schedule shift.

After 8 weeks, the researchers found stark differences among the old animals in the groups. While 83 percent of those animals survived under the normal schedule, only 47 percent in the forward-shift group and 68 percent in the backward-shift group made it through the experiment. Nearly all the middle-aged mice lived on, regardless of their light schedules.

Block reports in the Nov. 7 Curreent Biology that stress--measured by the amounts of stress-signaling chemicals in the rodents' feces--didn't seem to play a part in the elderly animals' demise. The team plans further experiments to determine what physiological effects the changing light schedules have on elderly animals.--C. B.