Shift Work Hazards

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Continuing Education Activity

Shift work enables businesses and organizations to maintain the pace of work and continuously provide access to goods and services throughout a 24-hour day. Approximately 25% of the adult workforce labors during non-traditional hours, including evenings, nights, early mornings, and weekends. Such work schedules disrupt the biological circadian rhythm and natural sleep-wake cycles. This disruption may cause significant consequences. A growing body of evidence shows a connection between shift work and numerous hazardous health outcomes, including both physical and mental health conditions. Shift work is also associated with increased workplace accidents, motor vehicle collisions, and burnout, posing a social risk. Occupations comprised mostly of shift workers, such as those in healthcare, should be cognizant of these hazards and take steps to mitigate risk. This activity reviews the hazards of shift work and discusses the role of the interprofessional team, organizational interventions, and individual behavioral changes aimed at reducing the risks associated with shift work.


  • Review common findings of sleep disturbances associated with shift work.
  • Summarize chronic health risks for those performing shift work.
  • Explain psychosocial challenges faced by shift workers.
  • Identify organizational and individual interventions to reduce the hazards of shift work.


Shift work enables businesses and organizations to maintain the pace of work and continuously provide access to goods or services throughout a 24-hour day. To operate continuously, companies usually divide the 24-hour day into discrete blocks of time, or shifts, during which groups of employees perform job duties. As one shift ends, another group of employees arrive, assume the job duties, and begin a new shift. A 24-hour operation requires companies to have employees present around the clock. There are numerous ways to organize shift schedules. This is tailored to suit the needs of a particular business. Variables include the length of the shift, start and end time, and whether shift patterns will be fixed or rotating.

According to the U.S. Department of Health and Human Services and the National Institute for Occupational Safety and Health, one standard method for organizing workers into shifts is to divide the 24-hour day into contiguous 8-hour blocks. An example of this method is:

  • 9 AM - 5 PM: First shift (also called "day shift" or "morning shift") 
  • 5 PM - 1 AM: Second shift (also called "afternoon shift" or "evening shift")
  • 1 AM - 9 PM: Third shift (also called "night shift" or "graveyard shift")

Another frequent method of organizing shift workers into shifts is to divide the 24-hour day into 12-hour blocks. An example of this method is:

  • 7 AM - 7 PM: First shift (also called "day shift") 
  • 7 PM - 7 AM: Second shift (or "night shift")

Most occupations do not have 24-hour shifts due to health and safety concerns. However, some first responders and certain healthcare providers remain notable exceptions.[1]

A fixed shift schedule is one in which there is no variation, and an employee works the same shift on the same day each week. An example of this is a nurse who works the day shift every week on Monday, Tuesday, Thursday, and Saturday. In contrast, some employees may work a rotating shift schedule in which shifts cycle through a progression. For example, an emergency room resident works mornings one week, evenings the next week, and nights the following week.[2] 

While variations exist in definitions for "shift work," it is generally agreed to refer to work hours outside of traditional business hours (approximately 9:00 AM to 5:00 PM). The term "shift worker" is most often used to describe individuals who work primarily during these nontraditional hours, especially at night. Individuals with nontraditional work schedules face additional physiologic and social challenges compared to those working traditional hours. A growing body of evidence demonstrates serious health, psychological, and societal consequences associated with shift work.[3]

Occupations primarily comprised of shift workers include service industries, healthcare professionals, first responders, transportation industries, and manufacturing industries. Roughly 25% of the adult workforce currently performs shift work, which is projected to continue increasing to keep pace with society's growing expectations and demands.[4]

Issues of Concern

Sleep and Fatigue

The circadian rhythm is mediated by the suprachiasmatic nucleus and plays a crucial role in normal sleep/wake physiology. Shift work is often in opposition to the regular circadian rhythm of workers, requiring them to maintain a sleep/wake cycle that is misaligned with natural physiology. Given this misalignment, shift workers are likelier to report sleep disturbances such as insomnia, poor sleep quality, and insufficient sleep duration when compared to dayshift workers. The prevalence of insomnia in shift workers is between 29% and 38%, compared to approximately 6% in the general population.[5] Not surprisingly, shift workers report higher levels of overall sleepiness when compared to dayshift workers.[6]

In some cases, shift workers may eventually develop clinically significant levels of distress, reduced social function, and impaired occupational performance. Frequent circadian rhythm disturbances may result in insomnia or sleepiness that is also accompanied by clinically significant levels of distress or impairment, known as Circadian Rhythm Sleep Disorder. When the cause of the circadian misalignment is due to atypical work hours, this is referred to as either “Shift Work Disorder” or “Shift Work Sleep Disorder.” [6] A study of 2,570 US shift workers between the ages of 18 and 65 demonstrated that 14% of night workers and 8% of rotating shift workers reported symptoms that met the shift work sleep disorder criteria.[7]

Shift workers often use days off to recover from reduced sleep. A single night without sleep requires approximately 1 to 2 nights of sleep to fully restore baseline levels of performance. After five nights with 4 hours of sleep per night, performance remained below baseline levels even after seven nights of recovery sleep. Additionally, insomnia, excessive sleepiness, and shift work disorder are associated with time off between consecutive shifts < 11 hours.[8][9]

Occupational Performance and Accidents

Sleep disturbances experienced by shift workers place them at an increased risk for accidents and work-related mistakes. Impaired cognition and decreased job performance are common complications of shift work found across several professions, including nurses, medical residents, pilots, truck drivers, and miners. Individuals frequently lack insight into the level of cognitive impairment that they may be experiencing.[6] Shift workers have an increased risk of occupational accidents, in some studies found to be nearly 3x greater. Hospital workers have demonstrated an increased risk of accidents during shifts longer than 8 hours and afternoon or night shifts.[10] The likelihood of inadvertently falling asleep on the job is also more common during the night shift. The probability of industrial and motor vehicle accidents peaks overnight and into the early morning hours. Shift workers commuting home after a shift is at an increased risk of motor vehicle collisions. Shift work-related accidents in transportation, manufacturing, healthcare, and other sectors pose a danger to shift workers and society at large.[6] 

Physical Health

A significant body of evidence shows adverse health consequences associated with shift work. Studies show an association between shift work and cardiovascular disease, metabolic syndrome, obesity, type II diabetes, gastrointestinal disturbances, asthma, erectile dysfunction, menstrual irregularities, pregnancy complications, breast cancer, prostate cancer, and colorectal cancer.[11] The exact role of shift work in the causality of chronic disease and the mechanisms through which shift work exerts influence remain unclear and are potential areas of future research.[12][13][14]

The atypical hours demanded of shift workers are associated with poor health habits, including physical inactivity, disruption of regular meal timing, and increased snacking.[15] A study of police officers on rotating shifts showed they consumed more caloric intake during nights at work.[16] Eating during the later portions of the circadian rhythm is associated with increased body fat and reduced effectiveness of weight loss.[6] Shift work has been implicated in impaired glucose tolerance, weight gain, and being overweight. Rotating shift workers exhibit a higher odds ratio for metabolic syndrome compared to their day worker counterparts. Reduced glycemic control has been noted. Female shift workers are at higher risk of developing metabolic syndrome and diabetes than male shift workers.[14] Increased risk for diabetes and hypertension is strongly associated with a rotating shift schedule, while the risk of developing obesity is higher in permanent night-shift workers.[6]

The International Agency for Research on Cancer has declared that night-shift work is “probably” carcinogenic for humans. Nurses with ≥ 20 years of rotating shifts and nurses with ≥ 15 years of night shifts demonstrated an increased risk for breast cancer[17] and rectal cancer, respectively. The risk of colorectal cancer demonstrates an 11% increase in risk for every five years of exposure to night work.[18][11]

Mental Health Concerns

Mental health and general well-being are adversely affected by shift work. Shift work commonly leads to challenges in maintaining social and family involvement due to scheduling conflicts. The deterioration of family and social involvement, coupled with the effects of circadian misalignment and sleep disruption, sets the stage for many mental health concerns.[19][20] Shift workers experience an increased prevalence of burnout, depression, anxiety, excessive sleepiness, insomnia, and suicidal ideation.[21][22]

Depression is more strongly associated with rotating shift work compared to fixed shifts. The amount of time between shifts and hours worked per week also affects mental health outcomes. Medical students who worked more than 55 hours/week were twice as likely to report suicidal ideations or mental health complications compared to doctors working 40 to 44 hours/week.[21]

Burnout results from improperly managed occupational stress. Emotionally demanding occupations such as nursing and law enforcement are particularly at risk. Burnout causes feelings of reduced energy or exhaustion, depersonalization from or negative feelings related to one’s job, and decreasing in workplace performance. In the case of healthcare workers, burnout has significant implications for the safety and well-being of patients.[23]

Clinical Significance

Impaired cognition and performance are common complications of shift work across many industries.[6] Lapses in attention and reduced performance in many occupations can have disastrous consequences. As a result, shift workers are at increased personal risk for associated hazards, and the elevated risk of workplace accidents and mistakes made by shift workers puts others at risk. Recognizing and addressing the hazards of shift work benefits both shift workers and society.

The healthcare setting is complex and full of pitfalls that may lead to workplace accidents. The high prevalence of shift work in healthcare is one factor that may contribute to unintentional accidents. As such, it would behoove healthcare companies to consider the well-being of employees in planning shift schedules.

The National Institute for Occupational Safety and Health recommends several interventions to improve the wellness of shift workers.[24] These measures include:

  • Avoid fixed, permanent night shifts
  • Limit consecutive night shifts to ≤ 3 in a row
  • Rotating shift work with forward rotation is preferred over backward rotation (i.e., days to evenings to nights preferred vs. nights to evenings to days)
  • Shifts > 12 hours should be avoided with ≤ 3 consecutive 12-hour shifts
  • Schedule ≥ 11 hours off between consecutive shifts to allow workers to rest
  • Provide regular weekends off without work to nourish family and social connections
  • Inform workers of schedules in advance and allow for adjustments if reasonable

Additional interventions to improve overall shift worker wellness include implementing sleep strategies for shift work, good sleep hygiene, bright light therapy, and potentially the addition of appropriate medication. If appropriate, napping during night shifts has been shown to reduce fatigue levels, increase alertness, and improve job performance. “Prophylactic naps” of 1 to 4 hours before night shifts have also demonstrated decreased sleepiness and improved performance. Exposure to light before and during a night shift suppresses the release of melatonin and helps maintain alertness and performance. Conversely, after completing a night shift, workers may benefit from wearing sunglasses or blue-light-blocking glasses to prevent exposure to light and improve the ability to fall asleep.[24]

Enhancing Healthcare Team Outcomes

Given the high-stakes nature of healthcare, preventing workplace accidents is of utmost importance. Even the most attentive and knowledgeable provider can make mistakes, especially when performing shift work. Having safeguards to prevent errors from reaching patients is critical to avoiding unintentional harm.

All providers (physicians, pharmacists, nurses, physician assistants, nurse practitioners, and technicians) are valuable members of the interprofessional team and are responsible for preventing mistakes from reaching the patient. Any team member may recognize a potential error and take action to prevent it. Creating a culture that encourages respectful, open, and non-judgmental communication amongst the interprofessional team promotes this collaborative behavior and improves patient safety.[25] Communication techniques such as closed-loop communication enhance patient safety and reduce verbal miscommunications that may result in accidents.[26] Collaboration between administration and healthcare providers improves hospital policies and standardizes workflows. Tools such as safety checklists, diagnostic algorithms, and medication verification help to reduce unintentional medical errors.[27]

While patients are often the primary victims of medical accidents, unintentional errors may also substantially impact the psychological health and well-being of healthcare providers.[2] Unintentional medical errors have implications for provider burnout, depression, PTSD, and suicide. Following an unintentional error, a supportive and understanding culture benefits those involved while they cope with the emotional aftermath.[28]



Janelle Thomas


1/27/2023 2:12:18 PM



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