Effect of age on sleep onset time in rotating shift workers

Abstract

Background: To determine the relationship between sleep onset time and age in rotating shift workers. Methods: Sleep diaries were used to record the sleeping onset time in rotating shift workers. Work shifts were rotated on a weekly basis and fell into three periods: morning (06:00–14:00 h), evening (14:00–22:00 h), and night (22:00–06:00 h). Work shifts were rotated in the following order: night, evening, and morning. One working week consisted of 5 days. The mean age of the male shift workers was 40.3 years. Results: A significantly earlier sleep onset time was observed in older workers working morning and evening shifts ( r=−0.42 and r=−0.66, respectively), but not when working night shifts ( r=−0.10). Regardless of age, night-shift workers usually go to sleep after their shift ends at 06:00 h. After the evening shift ends at 22:00 h, older workers tend to go to sleep earlier than younger workers. Conclusions: Sleep onset time becomes earlier with age in morning- and evening-shift workers. The morning shift starts very early, at 06:00 h, so workers must go to sleep very early to obtain an adequate amount of sleep. Older workers may go to sleep earlier because of physiological (circadian) and/or social factors associated with shift work.