Timed bright-light exposure and complaints related to shift work among women

Objectives This field study measured whether repeated, brief exposures to bright light during night shifts improved subjective well-being during and after night work. A secondary objective was to investigate whether this response differed by season (summer or winter), seasonality, or age. Methods Eighty-seven healthy female nurses were voluntarily exposed to brief periods (4x20 minutes) of bright (5000 lux) light at scheduled times during every night shift over a 2-week period. Each morning following a night shift the subjects filled out self-assessment questionnaires measuring subjective symptoms and distress caused by work at night. The questionnaires were also completed 2 weeks before and after the light intervention. The study had two phases, summer (May-June) and winter (November-December). Thirty-seven of the subjects participated during both periods. Results Light significantly alleviated the subjective distress associated with nightshift work, both in summer and in winter, independent of the subject's age. The effect was stronger for those who reported routine seasonal changes in mood. Conclusions Short pulses of timed bright-light exposure may enhance subjective adaptation to night work.