Abstract
Subjects working a 12h night shift offshore 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 the 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 19.00-07.00h (n=4) or 18.00-06.00h (n=6) offshore shift schedules. They were assessed for the last 7 days of a 14 or 21 day night shift offshore 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 night shift, theoretically timed to advance the circadian system. Subjects wore an Actiwatch-L throughout the study to monitor light and activity and completed daily sleep diaries. Actigraphic sleep efficiency after the light/sunglasses treatment was significantly improved (days 1-5) 86.7 ± 5.8% (light treatment) compared to the no light treatment leg 79.4 ± 10.3% (mean ± SD) P < 0.05. Subjective and objective sleep duration (days 6-14) was significantly improved in the light treatment leg; actigraphic sleep duration was longer after light treatment (6.75 ± 0.50h) compared to 5.76 ± 0.73h, P < 0.05, whilst subjective sleep duration was 8.05 h ± 0.72h compared to 7.32 ± 0.55h, respectively, P < 0.05. If appropriately timed, light and darkness has beneficial effects on sleep efficiency and sleep duration following a night shift.