Returning from night shift to day life: Beneficial effects of light on sleep

Subjects working a 12 h offshore night shift for 2 weeks normally adapt to the night shift and are out of synchrony when they return home to day life, with consequent problems of poor sleep. The aim of this study was to investigate the effectiveness of timed light treatment to hasten circadian adaptation and improve sleep after the night shift. Ten male shift workers worked 19.00-07.00 h (n = 4) or 18.00-06.00 h (n = 6) offshore shift schedules. They were assessed for the last 7 days of a 14 or 21 day offshore night shift and for the following 14 days at home. Either timed light treatment/sunglasses or no light treatment/no sunglasses were scheduled in a crossover design during days 1-5 after the nightshift, theoretically timed to advance the circadian system. Subjects completed the Horne Ostberg questionnaire. They wore an Actiwatch-L throughout the study to monitor light/activity and completed daily sleep diaries. Actigraphic sleep efficiency after the light/sunglasses treatment was significantly improved (days 1-5), that is, 86.7 +/- 5.8% (mean +/- SD; light treatment) compared to 79.4 +/- 10.3% (no light treatment), P < 0.05. Objective sleep duration (days 6-14) was significantly improved in the light treatment leg; actigraphic sleep duration was longer after light treatment (6.75 +/- 0.50 h) compared to 5.76 +/- 0.73 h, P < 0.05. If appropriately timed, light and darkness has beneficial effects on sleep efficiency and sleep duration following a night shift.