Biological Rhythms, Shiftwork, and Occupational Health

Abstract

“… and God divided the light from the darkness, and God called the light day , and the darkness He called night . And the evening and the morning were the first day” (Genesis 1:4–5, King James Version). So from the beginning, day/night periodicity has been an important environmental influence on life on earth. For diurnal species, like human beings, the sunlight portion of the day is the time for activity and the dark, nighttime for sleeping. Although we are under the influence of environmental rhythms, such as the daylight–night cycle, we are also under the physiological influence of our own internal biological clock. Normally synchronization of biological rhythms with each other and with environmental rhythms (external time cues) maximizes our waking and sleeping performance and promotes overall well‐being. Night work is opposed to the innate drive to sleep at night and work during the daytime and results in an unnatural mismatch of environmental and internal time cues. Shiftworkers are exposed to disruptive effects of schedule‐related time shifts on the normal synchronization of individual biological rhythms with each other as well as with the external time cues. This chapter reviews basic chronobiological principles as they relate to shiftworker safety and health. Studies dealing with the effects of time shifts on sleep, alertness, and performance rhythms are discussed. Research exploring the consequences of shiftwork on physical and mental health is reviewed. Countermeasures for minimizing adverse health and safety effects of sleep deprivation and biological rhythm disruption are presented. Industrial hygiene considerations related to control of worker exposure to potential toxins during extended and rotating shifts are considered. Finally, international and U.S. regulatory policy regarding shiftwork scheduling and special medical provisions for shiftworkers are reviewed.