Shift work

Type of Psychology: Biological bases of human behavior; Clinical; Counseling; Consulting; Health; Organizational; Social

Shift work constitutes any regular work schedules that occur outside of the traditional 9-to-5 day shifts, and is rapidly becoming more common. Shift work can result in impaired psychological functioning and increased risk for psychiatric and medical morbidities, and therefore is an important area of research. Other common consequences include disturbed sleep, reduced alertness during work, reduced work performance, reduced quality of life, and increased risk of accidents. These consequences may be addressed with some combination of alternative shift scheduling, behavioral interventions to improve daytime sleep, controlled light exposure, and medication use.

Shift work is an often overlooked area of study that has great relevance to psychological health and functioning. As the economy globalizes, the demand for a twenty-four-hour workforce also grows, resulting in a more employees working outside the traditional 9-to-5 day shift. In fact, as many as one out of four workers in the United States begin their shift between 2 pm and 6:30am, with an estimated thirty-eight million individuals engaging in regular shift work. More importantly, a notable proportion of shift workers are involved in safety-sensitive operations, such as traffic control, transportation, or management of power stations. As such, it is important to understand the consequences that shift work may have on psychological health and functioning. In fact, several historical events have pointed to the disastrous consequences associated with shift work–related impairments. Examples include Exxon Valdez, Chernobyl, and the American Airlines flight 1420 crash, all of which occurred during the night shift. Given the growing demand for shift work and the elevated vulnerability for impaired psychological functioning, increasing attention has been paid to shift work and its consequences.

The Biology of Shift Work

Although many shift workers experience difficulties in work performance and health complication, not everyone reports such difficulties. The prevailing theory is that individuals who report difficulties experience a misalignment between their internal circadian rhythm and their work schedules. Specifically, the human sleep-wake system is partially governed by an internal biological clock that regulates a host of physiological and psychological functions that fluctuates across the twenty-four-hour day. One example of an important function is alertness, which usually increases as the morning progresses, and decreases later in the day. This internal clock is generally calibrated based on exposure to natural sunlight (or manufactured bright light), and occurs relatively independent of sleep. This explains why individuals will often report a resurgence of energy in the morning, even after a night of sleep deprivation. Exposure to bright light also suppresses the production of melatonin, an endogenous hormone that promotes sleep.

Workers on the traditional day shift are generally operating on a schedule that is well aligned with their internal rhythms; going to bed at night and waking in the morning with the ebb and flow of alertness governed by their circadian rhythms. However, individuals working outside of the day shift are often attempting to remain vigilant and functional when their circadian rhythms are down-regulating alertness and up-regulating sleep-related processes. Similarly, these workers are also often attempting to sleep during the daytime, when their circadian rhythms are promoting wakefulness and its associated functions. Consequently, shift workers often report decreased amounts and poorer quality sleep relative to day workers. Moreover, the impairments from circadian misalignment are further compounded by a cumulative amount of sleep debt that is accrued over multiple days of poor and inadequate sleep.

Consequences of Shift Work

Shift Work Disorder. A range of consequences may occur as a result of misalignment between one's work schedule and circadian rhythms. While some people are able to adjust appropriately, many workers experience decreased task performance, with some even developing medical and psychiatric morbidities. Most notably, some individuals experience impairments that meet criteria for Shift Work Disorder (SWD). According to the International Classification of Sleep Disorders Criteria, SWD is characterized by insomnia and/or excessive sleepiness resulting from shift work that has been on-going for at least three months. Because much of human physiology is also governed by a biological clock, shift workers may also experience dysregulated physiological functioning, including increased insulin resistance, malabsorption, gastrointestinal difficulties, electrolyte imbalance, obesity, increased inflammation, and cardiovascular illness.

Reduced Sleep Time. Shift workers commonly report an average of between one to three hours less sleep than day workers, mostly as a function of attempting sleep during times when their circadian rhythms are promoting wakefulness. It is also not uncommon for shift workers to curtail sleep due to family or social obligations. A myriad of research on sleep loss has pointed to immediate and notable impairments. It has been shown that as little as three hours of sleep loss can result in driving impairments comparable to that occurring at legal limits of alcohol intoxication. This level of impairment is a likely explanation for the 50 percent increase in risk for automotive accidents in shift workers according to researchers. Similarly, neurocognitive performance also degrades with sleep loss, including decreased vigilance, reduced response times, increased errors, reduced capacity for error correction, and impaired learning and memory.

Insomnia. In addition to reduced sleep time, shift workers also reported poor quality sleep. This often manifests as difficulty falling or staying asleep. For some individuals with vulnerabilities to insomnia (e.g., family history, increased sleep reactivity to stress, etc.), shift work may be a precipitating factor for the onset of insomnia. In fact, in a 2004, large epidemiological study of the greater Detroit area, 18.5 percent of night workers reported clinically significant insomnia, which was more than twice the reported rate of insomnia in day workers. In addition to its immediate consequences, insomnia is also a significant risk factor for comorbid psychiatric illnesses such as depression and anxiety, as well as cardiovascular illness such as hypertension. In fact, recent evidence from 2014 suggests that individuals suffering from insomnia are at 45 percent increased risk for mortality from cardiovascular illness.

Sleepiness. Sleepiness is also commonly reported in shift work, and is a major contributing factor to occupational difficulties and decreased quality of life. As expected, shift workers both report and demonstrate increased sleepiness relative to day workers. A study comparing nurses working various shifts found that as high as 35 percent of nurses working the night shift report accidentally falling asleep at work, compared to only 3 percent in nurses working the day or evening shift.

Impaired Information Processing. Sleepiness can also adversely impact work performance due to impaired information processing. In fact, research has demonstrated reduced brain activation following sleep deprivation, particularly in regions responsible for executive functioning. This may explain why several domains of attention are generally negatively impacted by sleep loss. Firstly, lapses in attention are more likely to occur during sleepiness, which is important because it detracts from one's ability to achieve and maintain work productivity, and increases risk for errors of omission. Furthermore, research has also indicated that sleepy individuals may experience hyper-reactivity to novel stimuli in the environment which may also result in increased distractibility. Finally, sleepiness has also been associated with impaired learning, as demonstrated by both decreased quantity of items recalled, and degradation in the quality of the memory recalled. Together, the consequences of reduced work performance from sleep loss and sleepiness in shift workers may trigger a cascade of events (poor performance review, job loss, etc.) that significantly impact quality of life and mental health.

Impaired affective (emotional) processing. In addition to impaired cognitive processing, sleepiness also impacts affective functioning. It has been established that sleep deprivation is related to decreased positive affect (feelings), such as cheerfulness or joviality, and increased negative affect (feelings), such as hostility. Moreover, imaging research has found that that sleep loss leads to reduced connectivity in the frontolimbic pathway, indicating that sleep deprived brains are less able to regulate emotions, particularly those that are negatively valenced. This translates to an amplification of emotional experiences, suggesting that shift workers who are sleepy have increased reactivity to stressors compounded by impaired stress management.

Sleep-deprived shift workers may also experience distortions in affective processing that impact social functioning. Prior research showed that, compared with non-sleep-deprived individuals, sleep-deprived individuals have more difficulty recognizing happy and angry facial expressions of low to moderate intensity. This is important because facial expressions carry substantial weight in determining appropriate social interactions, and can have damaging consequences if misconstrued. For example, failure to repair ruptures in relationships with coworkers can lead to brewing discontentment and decreased workplace morale, as can failure to share or celebrate with a colleague's happiness. Additionally, sleep-deprived individuals may also be more distracted by negative stimuli that are task-irrelevant, suggesting that shift workers may be more distracted by environmental or social stressors at work, even if it does not impact their task at hand.

Sleep-dependent changes in positive affect are also relevant to psychological functioning and health. In particular, sleep-deprived individuals may show increased risk taking behaviors. Prior research has demonstrated that sleep deprived individuals had increased sensitivity to reward and decreased aversion to punishment following sleep-loss. This may lead to impulsive decisions and high-risk behaviors that can result in long-term negative outcomes. In fact, some individuals may even experience hypomania or mania symptoms following sleep-deprivation.

Accidents. Sleep-loss and sleepiness in shift work is also associated with increased risk for accidents that result in property damage, injury, or even death. Most notable accidents are related to falling asleep behind the wheel. This is particularly relevant to night and early morning shift workers. Night shift workers with a misalignment between their endogenous circadian rhythms and their work schedules are likely commuting during the early morning hours, when their circadian alertness is at the lowest. Early morning-shift workers are also at increased risk for sleepy driving during their commute to work due to reduced sleep time.

Accidents do not have to be confined to falling asleep at the wheel. Studies in medical personnel working unconventional shifts have found increased rates of percutaneous injuries from sharp medical instruments increased diagnostic and medication errors as well as increased rates of patient death. Furthermore, reported sleep disturbances have been shown to significantly predict both increased risk of injury and accidental death at work.

Medical Morbidities. Due to that fact that most physiological systems have a circadian component, shift-workers are often at increased risk for medical morbidities due to dysregulated functioning of these systems. Hunger, food preference, and metabolism are important examples of biological systems that have a strong circadian component. Consequently, shift-work has been associated with poor eating habits, increased risk of duodenal ulcers, and increased cardiovascular morbidity and mortality. Similarly, shift work may also increase risk for cancer. For example, large prospective studies have noted a 36% to 60% increase risk for breast cancer. Though studies of the underlying mechanisms are still underway, it has been suggested that a mediating factor in the relationship between shift work and cancer risk may be a reduction of free radical scavenging related to melatonin suppression from exposure to nocturnal light. In turn, the reduction of free radical scavenging leads to a reduced tumor-inhibition.

Interventions

Adjustments in shift scheduling. There are a number of ways in which the impairments from shift work can be addressed. One way is through adjustments to the type of shift work. While it is generally thought, and even advised, that permanent night-shift may improve outcomes due to its stability, there is little evidence to support this. In fact, both objective and subjective measurements of sleep indicated that night shift workers show greater reductions in sleep duration compared to evening and slower rotating shift workers. In terms of rotating shifts, adjustments can be made to both direction (shifts that progress with earlier versus later start times) and speed (the rate and increment of each change in shift start time). Most individuals are likely to respond better to forward-rotating rather than backward-rotating shifts. This is because the majority of individuals possess an endogenous circadian rhythm that is slightly longer than 24 hours, which in the absence of bright light leads in a natural delay every twenty-four hours. This means that when light exposure is purposefully controlled, delaying circadian rhythms can be achieved with relative ease. Slower-rotating shifts, such as those with three of more weeks per shift schedule, have also been associated with increase sleep time in workers relative to rapid-rotating shifts (e.g., multiple rotations within a week), suggesting better work performance and health outcomes.

Improving sleep. Given that sleep disturbance and insomnia is common in shift work, improving sleep quantity and quality can also aid in reducing work and health impairments. It is often recommended for shift workers to increase sleep opportunities in ways that also allow for personal, social, and familial obligations to be met. This can sometimes be achieved using two sleep periods. The first period is considered an “anchor” sleep, which is scheduled to occur every day (even during off-days), and would typically last approximately four hours. Ideally, daily obligations should be scheduled outside of the anchor sleep. The second sleep period would last another three to four hours, and can be taken at irregular times depending on work and other responsibilities. In cases where the sleep difficulty is related to insomnia, seeking treatments such as Cognitive Behavioral Therapy for insomnia can help individuals address issues with falling and staying asleep in the context of shift-work.

Studies have also shown that naps prior to the start of shift-work may be an effective countermeasure that improves alertness and performance during the shift, as this would allow for some dissipation of sleep pressure prior to work. Other studies have also found that naps in combination with caffeine use can also reduce workplace sleepiness and improve work performance.

Light. Interventions using deliberate and appropriate timing of bright light exposure (~10,000 lux at the cornea) have also gained empirical support. Because endogenous circadian rhythms are usually calibrated by natural sunlight, this can be harnessed via the use of artificial bright light. Exposure to bright light close to bedtime can induce a phase delay of the internal clock, whereas exposure to bright light approximately two hours before habitual wake time, or closely after the habitual wake time, can induce a phase advance. When used appropriately, each hour of exposure to bright light should incur a thirty-minute shift in the biological clock. Alternatively, the use of light blocking goggles can also be helpful, such as during instances when shift workers need to run errands during daylight shortly before their scheduled sleep time.

Melatonin and Medications. The use of exogenous melatonin can also be used to aid in sleep timing. When endogenous melatonin levels are low (typically during the day), administration of exogenous melatonin between doses of 1.0 and 10 mg can increase total sleep time. Use of exogenous melatonin paired with dim-light prior to scheduled sleep time can also aid in sleep promotion during the day.

Benzodiazepines have also been used to aid in daytime sleep, with research showing that individuals on simulated shift-work were able to improve daytime sleep by thirty to sixty minutes a day using benzodiazepines, though this did not appear to improve alertness during the night. On the other hand, alerting medications such as modafinil can also be used to improve various outcomes in shift work, including sleepiness while driving, psychomotor vigilance, as well as objectively defined sleepiness based on the Multiple Sleep Latency Test.

Bibliography

Belcher, Ren, Valentina Gumenyuk, and Thomas Roth. "Insomnia in Shift Work Disorder Relates to Occupational and Neurophysiological Impairment." Journal of Clinical Sleep Medicine 11.4 (2015): 457–65. PDF file.

Kalmbach, D. A., et al. "Shift Work Disorder, Depression, and Anxiety in the Transition to Rotating Shifts: The Role of Sleep Reactivity." Sleep Medicine 16.12 (2015): 1532–538. Print.

Kryger, M. H., et al. Principles and Practice of Sleep Medicine. Philadelphia: Saunders, 2005. Print.

Monk, T. H., and S. Folkard. Making Shift Work Tolerable. Boca Raton: CRC, 1992. Print.

"Work Schedules: Shift Work and Long Hours." National Institute for Occupational Safety and Health. Centers for Disease Control and Prevention, 5 Aug. 2015. Web. 28 June 2016.