Shift Work and Sleep

In today’s competitive economy, an increasing number of U.S. businesses operate to meet customer demand for 24/7 services. These around-the-clock operations are required in order to maintain a place in the global market where transactions with clients, suppliers, and colleagues can span multiple time zones.  Consequently, for many men and women, the workday no longer fits the traditional 9-to-5 model.  They may clock in at midnight and out at 8 in the morning, or they may follow a rotating shiftwork schedule consisting of periodic day shifts, evening shifts, and night shifts.

Since our body clocks typically are set for a routine of daytime activity and nighttime sleep, working irregular shifts or night hours can be associated with disrupted or insufficient sleep. In turn, drowsiness, fatigue, and circadian rhythm disruption from too little sleep or interrupted sleep are associated with risks for dysfunction of the immune system, diabetes, cardiovascular disease, and other chronic health problems.  As nontraditional schedules become more common, it becomes increasingly important to understand who may be at risk of unintended job-related outcomes, and why.  From that knowledge, employers, workers, and practitioners can better craft practical, effective interventions.

Scientists know little about the prevalence of sleep disorders broadly in the U.S. workforce because, to date, most studies have been limited to selected occupational groups, geographic areas, and types of sleep disorders. In a study published on-line earlier this month in the peer-reviewed journal Occupational & Environmental Medicine, we designed a larger investigation that would not be subject to those limitations.  We used data from the National Health and Nutrition Examination Survey (NHANES), conducted by the National Center for Health Statistics, one of our partner centers in the U.S. Centers for Disease Control and Prevention.

Ours was the first-ever study using a nationally representative sample of the U.S. working population to examine the role of shift work in sleep quality, sleep-related activities of daily living, and insomnia.

Our nationally representative sample included 6,338 adults, 18 years of age and older. They were asked to complete a survey questionnaire covering sleep duration, sleep disorders, sleep quality, impairment of sleep-related activities of daily living (ADL), and insomnia.  To determine the shift schedule worked by each individual, they were asked which choice best described the hours they usually worked: regular daytime (any hours between 6 a.m. and 6 p.m.), regular evening shift (any hours between 4 p.m. and midnight), regular night shift (any hours between 7 p.m. and 8 a.m.), rotating shift, or another schedule.  Based on a recommendation by the National Sleep Foundation that adults should sleep seven to nine hours per night, we created two categories of sleep duration for the study: either less than seven hours referred to as short sleep duration, or seven or more hours.

From our study of this large, nationally representative sample, we concluded that sleep-related problems were common among workers, especially among night-shift workers who had the highest risks for sleep problems. Moreover, these risks among night-shift workers persisted even after we adjusted for potentially confounding factors, such as long working hours, socio-demographic characteristics, and health/lifestyle/work factors.  Findings included these:

• 37.6 percent of the respondents reported short sleep duration, representing 54.1 million U.S. workers. Short sleep duration was more prevalent among night-shift workers (61.8 percent of those who reported short duration) than among daytime workers (35.9%).
• Daytime workers had the lowest prevalence (31 percent) of “prolonged sleep-onset latency,” which is when at bedtime 30 or more minutes are required to go from full wakefulness to sleep — compared with the night shift (46.2 percent), evening shift (43 percent) and rotating shift (42.1 percent).
• Poor sleep quality was reported by 30.7 percent of night-shift workers, and moderate sleep quality by 34.1 percent of workers on another schedule. Night- and evening-shift workers more frequently had difficulty falling asleep (21.7 percent and 21.2 percent, respectively, vs. 12.7 percent of daytime workers). Night-shift workers had a higher prevalence of feeling excessively or overly sleepy during the day (22.3 percent vs. 16.2 percent).
• Insomnia, which is defined as having both poor sleep quality and impaired sleep-related ADL, was reported by 18.5 percent of night-shift workers compared to 8.4 percent of daytime workers.
• Workers 60 years old or older had a lower prevalence of short sleep duration, impaired sleep-related activities of daily living (ADL), and insomnia than those 30 to 59 years old.
• Female workers had a lower prevalence of short sleep duration but a higher prevalence of the other three sleep outcomes (poor sleep quality, impaired sleep-related ADL, and insomnia) than male workers.
• Obese workers had a higher prevalence of short sleep duration and poor sleep quality than those who were normal weight/underweight.
• Current smokers had a higher prevalence of short sleep duration, poor sleep quality and insomnia (but not impaired sleep-related ADL) than non-smokers.
• Workers who worked 48 hours or more per week had a higher prevalence of short sleep duration, poor sleep quality and insomnia than those who worked less than 48 hours per week.
• Workers who frequently used sleeping pills had a higher prevalence of poor sleep quality, impaired sleep-related ADL and insomnia (but not short sleep duration) than those who did not.
• A higher prevalence of all four sleep outcomes (short sleep duration, poor sleep quality, insomnia, and impaired sleep-related ADL) was observed among workers who were widowed, divorced or separated; workers who reported fair or poor health; workers with symptomatic depression; and workers who had a physician-diagnosed sleep disorder – than among workers who did not have those characteristics.

Although our study was not subject to limitations of earlier investigations with smaller sample sizes, it was subject to other limitations inherent in the kind of investigation we conducted. We describe those limitations in our paper.  As we note there, they are mitigated to some degree by the consistency of our methods and findings with those of other well-designed studies in the literature.

Particularly in light of the likely continuing increase in nontraditional working schedules, work-based prevention strategies and policies should be adopted to improve the quantity and quality of sleep among workers. Unfortunately, there is no single ideal strategy to successfully address the sleep risks of every demanding shiftwork situation. Instead, interventions often need to be customized to the specific employer and worker.  These include designing new shift schedules with frequent rest breaks, avoiding night shifts that exceed eight hours, improving one’s sleep environment, taking a long nap before a night shift begins, accelerating the modulation of circadian rhythms using bright lights, improving physical fitness, engaging in stress reduction activities, and strengthening family and social support.  Sources of further information and recommendations from NIOSH can be found on the Work Schedules: Shift Work and Long Hours topic page.  What challenges have you found with night shifts, and what approaches have you used?

Geoffrey Calvert, MD, MPH, FACP

Dr. Calvert is a Team Leader and Senior Medical Epidemiologist in the NIOSH Division of Surveillance, Hazard Evaluations, and Field Studies