A Compromise Circadian Phase Position for Permanent Night Work Improves Mood, Fatigue, and Performance

STUDY OBJECTIVE: To assess night shift improvements in mood, fatigue, and performance when the misalignment between circadian rhythms and a night shift, day sleep schedule is reduced. DESIGN: Blocks of simulated night shifts alternated with days off. Experimental subjects had interventions to delay their circadian clocks to partially align with a night shift schedule. Control subjects had no interventions. Subjects were categorized according to the degree of circadian realignment independent of whether they were in the experimental or control groups. Twelve subjects were categorized as not re-entrained, 21 as partially re-entrained, and 6 as completely re-entrained. SETTING: Home sleep and laboratory night shifts. PARTICIPANTS: Young healthy adults. INTERVENTIONS: Experimental subjects had intermittent bright light pulses during night shifts, wore dark sunglasses outside, and had scheduled sleep episodes in darkness. MEASUREMENTS AND RESULTS: A computerized test battery was administered every 2 hours during day and night shifts. After about one week on the night shift schedule, which included a weekend off, the partially and completely re-entrained groups had markedly improved mood, fatigue, and performance compared to the group that was not re-entrained. The completely and partially re-entrained groups were similar to each other and had levels of mood, fatigue, and performance that were close to daytime levels. CONCLUSIONS: Partial re-entrainment to a permanent night shift schedule, which can be produced by feasible, inexpensive interventions, is associated with greatly reduced impairments during night shifts.