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Overtime and Extended Work Shifts:Recent Findings on Illnesses, Injuries, and Health BehaviorsClaire C. Caruso, Ph.D., R.N.Edward M. Hitchcock, Ph.D.Robert B. Dick, Ph.D.John M. Russo, Ph.D.Jennifer M. Schmit, M.A.U. S. Department of Health and Human ServicesCenters for Disease Control and PreventionNational Institute for Occupational Safety and HealthApril 2004

Overtime and Extended Work ShiftsOrdering InformationTo receive documents or other information about occupational safety and health topics,contact the National Institute for Occupational Safety and Health (NIOSH) atNIOSH Publications Dissemination4676 Columbia ParkwayCincinnati, OH 45226-1998Telephone: 1-800-35-NIOSH (1-800-356-4674)Fax: 1-513-533-8573E-mail: [email protected] visit the NIOSH Web site at www.cdc.gov/nioshThis document is in the public domain and may be freely copied orreprinted.Disclaimer: Mention of any company, product, policy, or the inclusionof any reference does not constitute endorsement by NIOSH.DHHS (NIOSH) Publication No. 2004-143ii

Recent Findings on Illnesses, Injuries, and Health BehaviorsForewordThe average number of hours worked annually by workers in the United States has increased steadily overthe past several decades and currently surpasses that of Japan and most of Western Europe. The influenceof overtime and extended work shifts on worker health and safety, as well as on worker errors, is gainingincreased 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 ofstates have been considering legislation to limit mandatory overtime for health care workers. The volumeof legislative activity seen nationwide indicates a heightened level of societal concern and the timelinessof the issue.This document summarizes recent scientific findings concerning the relationship between overtime andextended work shifts on worker health and safety. The number of studies increased dramatically over thepast few years, but important research questions remain. I am confident that this document will contributeto an informed discussion of these issues and provide a basis for further research and analysis.John Howard, M.D.Director,National Institute for Occupational Safety and Healthiii

Overtime and Extended Work ShiftsExecutive Summaryvigilance on task measures, and increasedinjuries. Two studies examining physicians whoworked very long shifts reported deterioration onvarious measures of cognitive performance.PURPOSEThis report provides an integrative review of 52recently published research reports that examinethe associations between long working hours andillnesses, injuries, health behaviors, and performance. The report is restricted to a description ofthe findings and methods and is not intended asan exhaustive discussion of all important issuesrelated to long working hours. Findings andmethods are summarized as reported by the original authors, and the study methods are not critically evaluated for quality.When 12-hour shifts combined with other workrelated demands, a pattern of more adverse findings was detected across studies. Six studiesexamining 12-hour shifts combined with morethan 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 andnight shifts reported that 12-hour night shiftswere associated with more physical fatigue,smoking, or alcohol use. Two studies examiningstart times for 12-hour shifts reported that decrements in alertness or more health complaintswere associated with early 6:00 a.m. start times.One study examining 12-hour shifts in hot workenvironments reported a slower pace of work ascompared with shorter shifts. Another studyexamining high workloads during 12-hour shiftsshowed increased discomfort and deterioration inperformance as compared with shorter shifts.SUMMARYIn 16 of 22 studies addressing general healtheffects, overtime was associated with poorer perceived general health, increased injury rates,more illnesses, or increased mortality. One metaanalysis of long work hours suggested a possibleweak relationship with preterm birth. Overtimewas associated with unhealthy weight gain in twostudies, increased alcohol use in two of threestudies, increased smoking in one of two studies,and poorer neuropsychological test performancein one study. Some reports did not support thistrend, finding no relationship between long workhours and leisure-time physical activity (two ofthree studies) and no relationship with drug abuse(one study).More definitive statements about differencesbetween 8-hour and 12-hour shifts are difficultbecause of the inconsistencies in the types ofwork schedules examined across studies. Workschedules differed by the time of day (i.e., day,evening, night), fixed versus rotating schedules,speed of rotation, direction of rotation, number ofhours worked per week, number of consecutivedays worked, number of rest days, and numberof weekends off. All of these factors could haveinteracted with overtime and influenced studyresults. Also, some studies did not report howmany hours participants worked per week orother details about the work shifts, which complicated the assessment of their results. The manyA pattern of deteriorating performance on psychophysiological tests as well as injuries whileworking long hours was observed across studyfindings, particularly with very long shifts andwhen 12-hour shifts combined with more than 40hours of work a week. Four studies that focusedon effects during extended shifts reported that the9th to 12th hours of work were associated withfeelings of decreased alertness and increasedfatigue, lower cognitive function, declines iniv

Recent Findings on Illnesses, Injuries, and Health Behaviorsdifferences in the 8- and 12-hour shift schedulesstudied may have accounted for their contradictory findings.Few studies have examined related topics, suchas the combined influence of shift work andovertime, or how worker control over their worktime and mandatory overtime might influencetheir health.Some studies examined functional abilities orinjuries during the 1st to 12th hours of work, butlittle has been reported about effects after the12th hour. Few studies have investigated theinfluence of long working hours on the healthand 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 managementand the course of common chronic diseases.Little data are available regarding the influenceof occupational exposures (i.e., chemical, heat,noise, lifting) in combination with long workinghours on health and safety.Although the number of published studies examining long working hours appears to be increasing, many research questions remain on howovertime and extended work shifts influenceworker health and safety.v

Overtime and Extended Work ShiftsTable of ContentsForeword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iiiExecutive Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ivTables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viiiAbbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ixAcknowledgments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . x1. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12. Description of the Work Schedules and the Samples. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33. Health and Safety Findings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53.1 Findings Associated with Overtime. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3.1a Overtime and Cardiovascular Findings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3.1b Overtime and Other Illnesses. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3.1c Overtime and Injuries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3.1d Overtime and Health Behaviors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3.1e Overtime and Performance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5581212123.2 Findings Associated with Extended Work Shifts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123.2a Extended Work Shifts and Illnesses. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173.2b Extended Work Shifts and Injuries. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173.2c Extended Work Shifts and Health Behaviors. . . . . . . . . . . . . . . . . . . . . . . 173.2d Extended Work Shifts and Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173.3 Findings Associated with Extended Work Shifts Combined with More than 40-HoursWork per Week . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213.3a Extended Work Shifts Combined with More than 40-Hours Work per Weekand Illnesses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213.3b Extended Work Shifts Combined with More than 40-Hours Work per Weekand Injuries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243.3c Extended Work Shifts Combined with More than 40-Hours Work per Weekand Health Behaviors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243.3d Extended Work Shifts Combined with More than 40-Hours Work per Weekand Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243.4 Findings Associated with Very Long Shifts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24vi

Recent Findings on Illnesses, Injuries, and Health Behaviors3.4a Very Long Shifts and Other Illnesses. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243.4b Very Long Shifts and Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 44. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274.1 Overtime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274.2 Extended Work Shifts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274.3 Other Work Schedule Characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284.4 Compensation, Vacation Time, Commute Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284.5 Gender and Age . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284.6 Chronic Health Problems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284.7 Occupational Exposures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295. Concluding Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31vii

Overtime and Extended Work ShiftsTablesTable 1. Countries Where Studies Were Conducted . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Table 2. Types of Work Investigated . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Table 3. Studies Examining Overtime and Cardiovascular Outcomes: Methods and Findings . . . . . . . . 6Table 4. Studies Examining Overtime and Other Illnesses: Methods and Findings . . . . . . . . . . . . . . . . 9Table 5. Studies Examining Overtime and Injuries: Methods and Findings . . . . . . . . . . . . . . . . . . . . . 13Table 6. Studies Examining Overtime, Health Behaviors, and Performance Outcomes: Methods andFindings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14Table 7. Studies Examining Extended Work Shifts: Methods and Findings . . . . . . . . . . . . . . . . . . . . . 18Table 8. Studies Examining Extended Work Shifts Combined with More than 40 Hours per week:Methods and Findings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22Table 9. Studies Examining Very Long Work Shifts: Methods and Findings . . . . . . . . . . . . . . . . . . . .25viii

Recent Findings on Illnesses, Injuries, and Health BehaviorsAbbreviationsANOVAanalysis of varianceANOCOVAanalysis of covarianceBMIbody mass indexBPblood pressureCIconfidence intervalCIRcumulative incidence ratioDdayDARTDivision of Applied Research and TechnologyEeveninghhourMmeanNnightNIOSHNationa