ABSTRACT
Humans are a diurnal species, habitually awake and active during the day and sleeping at night. However, modern society has changed this normal state for many workers. A variety of shift work schedules ranging from permanent or fixed night shifts to many different types of rotating shifts are currently used in a wide range of facilities and industries that require round-the-clock operation. Not surprisingly, much research has been devoted to examining the effects of shift work on sleep, alertness, performance, health, and well-being. One major concern with shift work is the impact of working at different times of the 24-hr day on the workers’ ability to sleep. As shown in the top portion of Figure 1, there are many factors that can influence the effect of shift work on sleep. In permanent shifts, the primary influence is the time of day that the shift takes place. The time of day that work is required can negatively impact endogenous circadian rhythms making it difficult for the workers to sleep during off-duty times. The ability to sleep while working rotating shifts is influenced by many factors (see bottom portion of Figure 1), one of which is the time of day. Rotating shifts are also influenced by the speed of shift rotation and the direction of shift rotation. In addition, the length of the shift may affect sleep in both permanent and rotating shifts.
