Physiological effects of rotational work shifting: a review. 
The high cost of capital equipment, demands of the world markets, and continuity requirements of many technological processes have forced industry to operate three-shift, 24-hour days.  Workers on fixed schedules experience no particular problems from shift work, but those who are shifted periodically can undergo physiological and emotional disturbances.  These disturbances occur because most human systems function according to circadian rhythms that can be easily disoriented.  The primary cause is the periodic shifting of the light-dark, wake-sleep cycles.  Extensive literature exists on the cause and symptoms of disturbances in the human physiological rhythms.  The information contained in this literature can be applied to protecting the health and well-being of the worker.