Disturbance of the Circadian System in Shift Work and Its Health Impact.

📖 Top 20% JournalDec 31, 2021Journal of biological rhythms

Disrupted Body Clock in Shift Workers and Its Effects on Health

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Abstract

Night-shift work may disrupt the body's internal clock significantly.

Shift work leads to abrupt changes in sleep and light exposure, affecting the circadian system.
Research shows that the circadian system may struggle to adapt from a day schedule to a night schedule.
There could be a misalignment between the circadian system and the external light-dark cycle due to night shifts.
Internal desynchronization within the circadian system may occur, affecting various biological rhythms.
Most human rhythmic transcripts may remain aligned with a day schedule, even after several days of night work.
Metabolites may shift by several hours during night work, leading to further misalignment with the circadian system.

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The various non-standard schedules required of shift workers force abrupt changes in the timing of sleep and light-dark exposure. These changes result in disturbances of the endogenous circadian system and its misalignment with the environment. Simulated night-shift experiments and field-based studies with shift workers both indicate that the circadian system is resistant to adaptation from a day- to a night-oriented schedule, as determined by a lack of substantial phase shifts over multiple days in centrally controlled rhythms, such as those of melatonin and cortisol. There is evidence that disruption of the circadian system caused by night-shift work results not only in a misalignment between the circadian system and the external light-dark cycle, but also in a state of internal desynchronization between various levels of the circadian system. This is the case between rhythms controlled by the central circadian pacemaker and clock genes expression in tissues such as peripheral blood mononuclear cells, hair follicle cells, and oral mucosa cells. The disruptive effects of atypical work schedules extend beyond the expression profile of canonical circadian clock genes and affects other transcripts of the human genome. In general, after several days of living at night, most rhythmic transcripts in the human genome remain adjusted to a day-oriented schedule, with dampened group amplitudes. In contrast to circadian clock genes and rhythmic transcripts, metabolomics studies revealed that most metabolites shift by several hours when working nights, thus leading to their misalignment with the circadian system. Altogether, these circadian and sleep-wake disturbances emphasize the all-encompassing impact of night-shift work, and can contribute to the increased risk of various medical conditions. Here, we review the latest scientific evidence regarding the effects of atypical work schedules on the circadian system, sleep and alertness of shift-working populations, and discuss their potential clinical impacts.

Key numbers

1.10

Increased Odds Ratio for Metabolic Syndrome

Pooled relative risk from a meta-analysis of 21 studies.

25%

Circadian Adaptation Rate

Estimated percentage of workers adapting to night shifts.

42%

Increased Risk of Depression

Increase in risk among night workers as reported in a meta-analysis.

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Abstract

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