Effects of nighttime nap and age on sleep patterns of shift workers

The effects of nighttime nap and age on sleep patterns of shift workers were examined for two groups of young and older guards working a 24-h shift with a nighttime nap of approximately 3.2 h. For both groups, day sleep was reduced by approximately 4.1 h, mainly affecting stage 2 sleep, slow wave sleep (SWS), and REM sleep. The totals of the different sleep stages of the nighttime nap plus day sleep were shorter than those of the control night only in stage 2 sleep. The nighttime nap appears to compensate for the sleep loss caused by night duty. During day sleep, the older subjects had relatively more awakenings and stage shifts. In the older group, the acrophase of oral temperature exhibited a significant phase advance of circadian rhythm, with reductions of means in the mesor and amplitude. Morningness-eveningness questionnaires tended to show higher scores (morningness) for the older group. From these results, it was determined that for older workers, an aberration in the phase of the circadian rhythm would slightly increase the difficulty of day sleep following night duty.