Sleep duration and quality in permanent night work: an observational field study.

Purpose: Permanent night workers conceivably show better adaptation of circadian rhythms to night work than shift workers and therefore better possibilities of obtaining sufficient sleep of good quality after night shifts. We investigated the effect of night shifts including number of consecutive shifts on sleep among self-selected permanent night workers, and studied if the effect of night shifts differed between morning and evening types and compared with 3-shift workers.

Methods: The study population included 90 permanent night workers followed for 14 days (warehouse workers, 1228 observation days, 80% males).