shift work

Effects on psychological and physical health

Most of the early work on the psychological outcomes of shift work focused on the exploration of shift workers’ attitudes, such as job satisfaction. This research suggests that, although workers welcome the idea of shift systems up front, they are typically less satisfied with their work than nonshift workers. Additionally, the research shows that psychological and emotional distress accompanies shift work. However, studies on the severity of these issues have not been conclusive.

A great deal of research has investigated the impact of shift work on individual circadian rhythms. Humans have evolved over thousands of years as a species that habitually sleeps during the night and is awake during the day. The rotation of Earth around the sun creates a 24-hour cycle of light and dark, which is internalized by humans and forms a natural internal body clock. All human circadian rhythms normally show a fixed-phase relationship. For example, body temperature peaks in the evening. In general, many bodily functions are at their highest level of activity during the day, allowing for a natural progression toward sleep at night.

Sleep problems occur for shift workers as a result of the mismatch between environmental time cues and the internal timing system. Although the natural light-dark cycle, the clock time, and other social cues may remain the same, the timing of shift workers’ work and sleep is delayed. Evidence suggests that adjustments to the shift workers’ body clocks are slow, if they occur at all. This mismatch between the environment and the internal body clock has been linked to negative outcomes such as sleep deprivation and chronic fatigue.

Chronic fatigue is linked with greater incidence of physical injury. A greater number of serious job-related injuries occur among employees who work night shifts. Night shift workers are more likely to be involved in automobile accidents on the drive home from work than day shift workers. While the link between work hours and increased risk of injury seems clear, several potential confounding factors must be considered for injuries sustained on the job. Significantly, night shift workers are often less experienced and work with less supervision than their daytime counterparts.

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By far the most prevalent health complaint associated with shift work is gastrointestinal problems. Irregular eating schedules and diminished access to healthful foods may in part account for this. The relationship between cardiovascular disease and shift work has also been explored. Many characteristics of shift workers are considered predictors of cardiovascular disease (e.g., poor eating habits, gastrointestinal disorders, sleeping disorders, less favorable working conditions). Shift work has additionally been shown to have negative effects on the reproductive cycles of women (e.g., increased menstrual pain and fertility problems). The physiological effects of shift work may also influence drug activity and effectiveness, suggesting that persistent shift work may be incompatible with the efficacious treatment of disease.

Social and domestic disruption

In addition to the psychological and physical effects, shift work is related to several social and domestic variables. For example, although organizations may believe that it is advantageous to operate on a 24-hour schedule, estimates place the cost of shift work among U.S. companies at tens of billions of dollars a year. Research has shown higher rates of absenteeism among shift working populations. Thus, the cost results in part from lost productivity because of absenteeism and higher medical bills because of increased injury and accidents. Additionally, shift work is associated with a decreased ability to balance work and nonwork responsibilities. Divorce rates for shift workers are substantially higher than those for day workers.

Variables among individual shift workers

Several individual difference variables have been shown to be important to the relationship between shift work schedules and outcomes. For example, “morningness,” or a preference for going to bed early and rising early in the morning, is moderately associated with difficulty adjusting to night work. Additionally, sleep flexibility (i.e., the ability to sleep at unusual times) and vigor (i.e., the ability to overcome drowsiness) predict an individual’s level of tolerance for shift work.

Individual differences in age and personality are also frequently investigated. The older an employee is, the less tolerance he or she will have for shift work. It has been recommended that shift work be voluntary after the age of 40. Over the age of 50, it becomes increasingly difficult for individuals to alter their sleep-wake cycles. Many physical ailments increase with advancing age, and this increase in physical problems affects older individuals’ ability to adjust to shift work. With regard to personality, it has been found that introverts are generally more morning-oriented than extroverts, making it more difficult for them to adjust to shift work.

Another individual difference variable that has been explored is the amount of social support an individual receives. Supervisor support has been found to be a crucial buffer to the negative effects of stress induced by shift work.