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NIOSH Publication No. 2004-143:Overtime and Extended Work Shifts: Recent Findings on
Illnesses, Injuries and Health Behaviors
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May 2004
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Table of Contents: Main PageTable 1. Countries Where Studies Were Conducted Table 2. Types of Work Investigated Table 3. Studies Examining Overtime and Cardiovascular Outcomes: Methods and Findings Table 4. Studies Examining Overtime and Other Illnesses: Methods and Findings Table 5. Studies Examining Overtime and Injuries: Methods and Findings Table 6. Studies Examining Overtime, Health Behaviors, and Performance Outcomes: Methods and Findings Table 7. Studies Examining Extended Work Shifts: Methods and Findings Table 8. Studies Examining Extended Work Shifts Combined with More than 40 Hours per week: Methods and Findings Table 9. Studies Examining Very Long Work Shifts: Methods and Findings Abbreviations Acknowledgments Introduction Description of Work Schedules and Samples Health and Safety Findings Summary Concluding Remarks References ForewordThe average number of hours worked annually by workers in the United States has increased steadily over the past several decades and currently surpasses that of Japan and most of Western Europe. The influence of overtime and extended work shifts on worker health and safety, as well as on worker errors, is gaining increased attention from the scientific community, labor representatives, and industry. U.S. hours of service limits have been regulated for the transportation sector for many years. In recent years, a number of states have been considering legislation to limit mandatory overtime for health care workers. The volume of legislative activity seen nationwide indicates a heightened level of societal concern and the timeliness of the issue. This document summarizes recent scientific findings concerning the relationship between overtime and extended work shifts on worker health and safety. The number of studies increased dramatically over the past few years, but important research questions remain. I am confident that this document will contribute to an informed discussion of these issues and provide a basis for further research and analysis. John Howard, M.D. Executive SummaryPURPOSEThis report provides an integrative review of 52 recently published research reports that examine the associations between long working hours and illnesses, injuries, health behaviors, and performance. The report is restricted to a description of the findings and methods and is not intended as an exhaustive discussion of all important issues related to long working hours. Findings and methods are summarized as reported by the original authors, and the study methods are not critically evaluated for quality. SUMMARYIn 16 of 22 studies addressing general health effects, overtime was associated with poorer perceived general health, increased injury rates, more illnesses, or increased mortality. One metaanalysis of long work hours suggested a possible weak relationship with preterm birth. Overtime was associated with unhealthy weight gain in two studies, increased alcohol use in two of three studies, increased smoking in one of two studies, and poorer neuropsychological test performance in one study. Some reports did not support this trend, finding no relationship between long work hours and leisure-time physical activity (two of three studies) and no relationship with drug abuse (one study). A pattern of deteriorating performance on psychophysiological tests as well as injuries while working long hours was observed across study findings, particularly with very long shifts and when 12-hour shifts combined with more than 40 hours of work a week. Four studies that focused on effects during extended shifts reported that the 9th to 12th hours of work were associated with feelings of decreased alertness and increased fatigue, lower cognitive function, declines in vigilance on task measures, and increased injuries. Two studies examining physicians who worked very long shifts reported deterioration on various measures of cognitive performance. When 12-hour shifts combined with other workrelated demands, a pattern of more adverse findings was detected across studies. Six studies examining 12-hour shifts combined with more than 40 hours of work per week reported increases in health complaints, deterioration in performance, or slower pace of work. Two studies comparing 8- and 12-hour schedules during day and night shifts reported that 12-hour night shifts were associated with more physical fatigue, smoking, or alcohol use. Two studies examining start times for 12-hour shifts reported that decrements in alertness or more health complaints were associated with early 6:00 a.m. start times. One study examining 12-hour shifts in hot work environments reported a slower pace of work as compared with shorter shifts. Another study examining high workloads during 12-hour shifts showed increased discomfort and deterioration in performance as compared with shorter shifts. More definitive statements about differences between 8-hour and 12-hour shifts are difficult because of the inconsistencies in the types of work schedules examined across studies. Work schedules differed by the time of day (i.e., day, evening, night), fixed versus rotating schedules, speed of rotation, direction of rotation, number of hours worked per week, number of consecutive days worked, number of rest days, and number of weekends off. All of these factors could have interacted with overtime and influenced study results. Also, some studies did not report how many hours participants worked per week or other details about the work shifts, which complicated the assessment of their results. The many differences in the 8- and 12-hour shift schedules studied may have accounted for their contradictory findings. Few studies have examined related topics, such as the combined influence of shift work and overtime, or how worker control over their work time and mandatory overtime might influence their health. Some studies examined functional abilities or injuries during the 1st to 12th hours of work, but little has been reported about effects after the 12th hour. Few studies have investigated the influence of long working hours on the health and safety of women or older workers. Few studies have explored how long working hours influence workers with pre-existing health problems, or how the hours relate to symptom management and the course of common chronic diseases. Little data are available regarding the influence of occupational exposures (i.e., chemical, heat, noise, lifting) in combination with long working hours on health and safety. Although the number of published studies examining long working hours appears to be increasing, many research questions remain on how overtime and extended work shifts influence worker health and safety. Ordering InformationTo receive documents or other information about occupational safety and health topics, contact the National Institute for Occupational Safety and Health (NIOSH) at NIOSH Publications Dissemination Telephone: 1-800-35-NIOSH (1-800-356-4674) This document is in the public domain and may be freely copied or reprinted. Disclaimer: Mention of any company, product, policy, or the inclusion of any reference does not constitute endorsement by NIOSH.
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(49 pages, 1.85MB)
