Meal-timing, circadian rhythms and life span of mice.

The possibility that circadian rhythm alteration may contribute to the life-prolonging effect of food restriction was investigated in female CD2F1 mice housed in a room with a 12-h span of fluorescent lighting daily. A control group was allowed to feed ad libitum throughout life while three other groups began lifelong restriction to about 75% of ad libitum intake when 6 wk old. The daily schedule of food accessibility differed among these three groups: a single meal during early darkness; a single meal during early light; six smaller meals at about 2-h intervals during darkness. Food restriction as such clearly prolonged life, but there were no statistically significant differences in overall mean life span or in 10th-decile life span among the three restricted groups. Telemetered body temperature data confirmed marked differences in the effects of these different restricted feeding schedules on circadian rhythms. The effect of food restriction on survival is probably not due to altered relations among circadian rhythmic variables. Possible contributing factors suggested by the results are a lower body temperature, a reduced overall metabolic rate and an increased circadian amplitude.