Sleep, age, and shiftwork experience.

The effects of age and shiftwork experience (never, past, present) on sleep were studied in a sample of 3236 wage earners and retired workers by means of a questionnaire. The sample was composed of 32-, 42-, 52-, and 62-year-old subjects, and included both sexes and various occupational statuses. Age resulted in a continuously increasing frequency of sleep disturbances and hypnotic use, except for difficulty getting back to sleep and early awakening, which peaked at 52 years and then decreased at 62 years, thus suggesting a 'retirement effect'. Current and past shiftworkers reported more problems with falling asleep and early awakening than subjects who had never worked on shifts. This is a likely explanation of why the effect of age was massive in the latter group and much less pronounced in the former groups. There were no clear effects of the length or recency of shiftwork experience. This finding does not support the hypothesized permanent effect of shiftwork experience on subsequent sleep. Females had higher complaint rates at every age. There was little interaction between age and sex, but women were affected more by shiftwork as they got older, particularly as to hypnotic consumption. Some of the results support the hypothesis that a selection process excludes workers who are no longer able to cope with the demands of shiftwork.