This study examined the short-term effects of shift work on mood changes. The subjects were 1 608 Japanese female nurses, working on rotating 3-shift schedules consisted of day, evening, and night shift. Repeated measurements of six dimensions of mood and sleep hours in four consecutive days were analyzed. Prominent changes of subjective fatigue, activity and confusion were observed especially when shift changes occurred (e.g., day shift to night shift or night shift to evening shift). The changes of mood were contingent to those of sleep hours, which suggested the close association between them. However, the mood changes were observed even after adjusting for the effect of sleep hours, indicating that irregular sleep pattern is not the only cause that affects mood.
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