Shift work

Shift work is an employment practice designed to make use of, or provide service across, all 24 hours of the clock each day of the week (often abbreviated as 24/7). The practice typically sees the day divided into shifts, set periods of time during which different groups of workers perform their duties. The term "shift work" includes both long-term night shifts and work schedules in which employees change or rotate shifts.[1][2][3]

In medicine and epidemiology, shift work is considered a risk factor for some health problems in some individuals, as disruption to circadian rhythms may increase the probability of developing cardiovascular disease, cognitive impairment, diabetes, and obesity, among other conditions.[4][5] Shift work can also contribute to strain in marital, family, and personal relationships.[6] A marriage where one partner works an irregular shift is six times more likely to end in divorce than a marriage where both partners work days.[7]

Health effects

A video on the health effects of shift work

Shift work increases the risk for the development of many disorders. Shift work sleep disorder is a circadian rhythm sleep disorder characterized by insomnia, excessive sleepiness, or both. Shift work is considered essential for the diagnosis.[8] The risk of diabetes mellitus type 2 is increased in shift workers, especially men. People working rotating shifts are more vulnerable than others.[9]

Women whose work involves night shifts have a 48% increased risk of developing breast cancer.[6][10] This may be due to alterations in circadian rhythm: melatonin, a known tumor suppressor, is generally produced at night and late shifts may disrupt its production.[10] The WHO's International Agency for Research on Cancer listed "shift work that involves circadian disruption" as a probable carcinogen.[11][12] Shift work may also increase the risk of other types of cancer.[13] Working rotating shift work regularly during a two-year interval has been associated with a 9% increased the risk of early menopause compared to women who work no rotating shift work. The increased risk among rotating night shift workers was 25% among women predisposed to earlier menopause. Early menopause can lead to a whole host of other problems later in life.[14][15] A recent study, found that women who worked rotating night shifts for more than six years, eleven percent experienced a shortened lifespan. Women who worked rotating night shifts for more than 15 years also experienced a 25 percent higher risk of death due to lung cancer.[16]

Shift work also increases the risk of developing cluster headaches,[17] heart attacks,[18] fatigue, stress, sexual dysfunction,[19] depression,[20] dementia, obesity,[8] metabolic disorders, gastrointestinal disorders, musculoskeletal disorders, and reproductive disorders.[6]

Children going to a 12-hour night shift in the United States, 1908

Shift work also can worsen chronic diseases, including sleep disorders, digestive diseases, heart disease, hypertension, epilepsy, mental disorders, substance abuse, asthma, and any health conditions that are treated with medications affected by the circadian cycle.[6] Artificial lighting may additionally contribute to disturbed homeostasis.[21] Shift work may also increase a person's risk of smoking.[6]

The health consequences of shift work may depend on chronotype, that is, being a day person or a night person, and what shift a worker is assigned to. When individual chronotype is opposite of shift timing (day person working night shift), there is a greater risk of circadian rhythms disruption.[22] Nighttime workers sleep an average of 1-4 hours less than daytime workers.[23]

Different shift schedules will have different impacts on the health of a shift worker. The way the shift pattern is designed affects how shift workers sleep, eat and take holidays. Some shift patterns can exacerbate fatigue by limiting rest, increasing stress, overworking staff or disrupting their time off.[24]

Muscle health is also compromised by Shift work: Altered sleep and altered eating times. Changes to appetite regulating hormones, more snacking and full center of the brain not working properly, changes in total energy expenditure. Increased snacking, increased binge drinking and reduced protein intake. All these factor can contribute to negative protein balance, increases in insulin resistance and increases in fat. Which can lead to weight gain and more long term health challenge.[25]

Compared with the day shift, injuries and accidents have been estimated to increase by 15% on evening shifts and 28% on night shifts. Longer shifts are also associated with more injuries and accidents: 10-hour shifts had 13% more and 12-hour shifts had 28% more than 8-hour shifts.[6] Other studies have shown a link between fatigue and workplace injuries and accidents. Workers with sleep deprivation are far more likely to be injured or involved in an accident.[8]

One study suggests that, for those working a night shift (such as 23:00 to 07:00), it may be advantageous to sleep in the evening (14:00 to 22:00) rather than the morning (08:00 to 16:00). The study's evening sleep subjects had 37% fewer episodes of attentional impairment than the morning sleepers.[26]

There are four major determinants of cognitive performance and alertness in healthy shift-workers. They are: circadian phase, sleep inertia, acute sleep deprivation and chronic sleep deficit.[27]

  • The circadian phase is relatively fixed in humans; attempting to shift it so that an individual is alert during the circadian bathyphase is difficult. Sleep during the day is shorter and less consolidated than night-time sleep.[8] Before a night shift, workers generally sleep less than before a day shift.[20]
  • The effects of sleep inertia wear off after 2–4 hours of wakefulness,[27] such that most workers who wake up in the morning and go to work suffer some degree of sleep inertia at the beginning of their shift. The relative effects of sleep inertia vs. the other factors are hard to quantify; however, the benefits of napping appear to outweigh the cost associated with sleep inertia.
  • Acute sleep deprivation occurs during long shifts with no breaks, as well as during night shifts when the worker sleeps in the morning and is awake during the afternoon, prior to the work shift. A night shift worker with poor daytime sleep may be awake for more than 18 hours by the end of his shift. The effects of acute sleep deprivation can be compared to impairment due to alcohol intoxication,[8] with 19 hours of wakefulness corresponding to a BAC of 0.05%, and 24 hours of wakefulness corresponding to a BAC of 0.10%.[6][28] Much of the effect of acute sleep deprivation can be countered by napping, with longer naps giving more benefit than shorter naps.[29] Some industries, specifically the fire service, have traditionally allowed workers to sleep while on duty, between calls for service. In one study of EMS providers, 24-hour shifts were not associated with a higher frequency of negative safety outcomes when compared to shorter shifts.[30]
  • Chronic sleep deficit occurs when a worker sleeps for fewer hours than is necessary over multiple days or weeks. The loss of two hours of nightly sleep for a week causes an impairment similar to those seen after 24 hours of wakefulness. After two weeks of such deficit, the lapses in performance are similar to those seen after 48 hours of continual wakefulness.[31] The number of shifts worked in a month by EMS providers was positively correlated with the frequency of reported errors and adverse events.[30]