Grant: Travel Awards - Institute Community Support

Individuals vary greatly in their capacity to adapt to night shift schedule resulting in reduced performance during their work period, and reduced sleep quality during their sleep period. The aim of the present study was to assess factors that contribute to a better circadian adaptation of night shift workers. Police officers (n=17) were studied during a series of 7 consecutive night shifts. Light exposure and sleep behaviors were collected throughout their working days. In addition, police officers were studied in laboratory before and after this series of night shift. This procedure was used to evaluate their circadian adaptation to 7 days of night shift work based on the secretion of melatonin, a reliable marker of circadian phase. For statistical analysis, participants were grouped based on their degree circadian adaptation. Compared to the non-adapted group, adapted police officers were younger, exposed to greater light intensities at night, tended to spent more time in bed in the daytime, and showed a more robust diurnal variation in melatonin level. Thus, Individual factors such as age and behavior of exposure to light and darkness affect the adaptation to night shift work.