Schedule-shifts, circadian rhythms and lifespan of freely-feeding and meal-fed mice.

Mice feeding ad lib were subjected to weekly 12-hr shifts of the daily light-dark (LD) schedule beginning at either 7, 20 or 52 weeks of age and continuing until death. Other mice were meal-fed and, from 7 weeks of age until death, experienced weekly 12-hr shifts of the LD schedule alone (with mealtime fixed) or of both the LD schedule and mealtime. Telemetered core temperature data indicated marked differences in response to the different shift conditions and suggested, in the case of meal-fed animals, involvement of a food-anticipatory rhythm. Shifting of the LD schedule had no statistically significant effect on the mean survival time of mice feeding ad lib, regardless of when shifting began. While meal-feeding in itself prolonged life, the added imposition of schedule-shifting had no statistically significant effect on mean survival time, regardless of whether the meal schedule reinforced or opposed shifts of the LD schedule. In the latter case, tenth-decile survival time may have been increased.