Gene Block, a professor of biology, and colleague Alec Davidson said they stumbled onto the findings by accident.Genetically engineered mice in another experiment died when they were put under lights six hours earlier than usual, but no mice died if the light schedule was delayed.
So they tested three groups of mice, with about 30 old mice and 9 young mice in each group.
One group had its light/dark cycle shifted forward by six hours — the equivalent of waking people up six hours early — every week for eight weeks.
A second group had its schedule shifted back by six hours, and the third group’s schedule was unaltered.
They found that 83 percent of old mice survived under the normal schedule, 68 percent lived after eight weeks of shifting steadily backward, but fewer than half — 47 percent — survived when the lights regularly came on six hours earlier.
When they speeded the schedule up, changing the light schedule every four days, even more mice died.
The mice were not obviously stressed by this — their daily levels of a stress hormone called corticosterone did not increase.