Environmental and occupational medicine, 4th edition. Rom WN, Markowitz SB, eds. Philadelphia, PA: Lippincott Williams & Wilkins, 2006 Dec; :1359-1363
A significant number of Americans are exposed to shift work and long work hours. Broadly defined, shift work involves work at times other than daytime hours of approximately 7:00 A.M. to 6:00 P.M. According to the U.S. Bureau of Labor Statistics, almost 15% of full-time workers (or 15 million Americans) work on evening, night, rotating, split, or employer-arranged irregular shifts (1). Estimates of the number of workers exposed to long work hours depend on how the term is defined. Based on a minimum of 50 hours per week, Jacobs and Gerson (2) estimated that over 26% of U.S. men and 11% of U.S. women worked long hours in 2000. Both social needs and economic factors promote the use of shift work and long hours. Shift workers provide critical services around the clock, including police and fire protection, health care, transportation, communications, public utilities, and military service. Other industries require continuous processing or operations to maximize the financial yield from capital investment in machinery and other production materials. There are also a multitude of economic factors driving long work hours including shortages of workers with specialized skills, temporary surges in workload, desire to avoid expenses connected with hiring additional staff, and worker desire for higher income. The relationship between work schedules and health and safety is complex and is influenced by characteristics of the work schedule itself as well as characteristics of the job, the worker, and the work environment (3). Ergonomic and organizational factors, job demands, workers' personalities, sociodemographic characteristics, geographic location, recreational resources, housing arrangements, sociometric patterns, and social support may act to influence or modulate the effects. Some studies of work schedules and health or safety outcomes have not accounted for these factors, which may partially explain the combination of positive, negative, and null effects reported in the literature. Some of these inconsistencies may also be attributed to limitations inherent in field research designs, but others reflect the subtleties and complexities of the work schedule's impact on worker adjustment (4,5). In addition, studies may be contaminated by crossover effects (e.g., when a shift worker moves to day shift and adverse effects continue on the day schedule) and selective attrition (the "survivor" or "healthy worker" effect) (6). Nonetheless, perusal of the literature suggests that some generalizations can be made about the risks potentially associated with demanding work schedules.