The relation of age to the adjustment of the circadian rhythms of oral temperature and sleepiness to shift work.

The relation of age to the adjustment of the circadian rhythms of oral temperature (T0) and sleepiness (S) in shift work was studied. 145 healthy female nurses underwent detailed laboratory and field measurements. Self-rated sleepiness, and oral temperature measured with a special extended-scale mercury thermometer, were recorded at 2 hr intervals during a morning (M) and 2 consecutive night (N) shifts. Sleeping times were registered during the same days. The results were analyzed separately in the age-groups of 22-29, 30-39 and 40-49-year-old subjects. From the morning shift to the second night shift day, the oral temperature and sleepiness acrophases shifted significantly (p less than 0.001) forward in all age groups. The amplitude decreased in the youngest and in the 30-39-year old age groups but not in the oldest age group. During the second night shift day, the acrophases and amplitudes of oral temperature rhythms were significantly different (P less than 0.05) between the groups, but there were no significant differences by age in the change of the circadian rhythms from morning to the second night shift days. The results thus fail to corroborate that physiological adjustment to night work would be influenced by age.