Reduced Tolerance to Night Shift in Chronic Shift Workers: Insight From Fractal Regulation

Aug 26, 2017Sleep

Lower Night Shift Adaptation in Long-Term Shift Workers Linked to Changes in Body's Natural Rhythms

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Circadian Biology on OpenScience ↗PubMed ↗DOI ↗

Abstract

Fractal regulation (FR) broke down in chronic shift workers during night shifts, leading to increased randomness in activity patterns.

Shift workers exhibited more random fluctuations in motor activity during night shifts compared to non-shift workers.
The disruption of FR was evident in shift workers even two days after the last night shift.
In controlled laboratory conditions, chronic shift workers showed greater susceptibility to circadian misalignment than non-shift workers.
Older age at the onset of shift work was associated with more severe perturbations in FR during both real and simulated night shifts.
Healthy physiological function is characterized by stable FR, which may deteriorate due to chronic shift work.

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STUDY OBJECTIVES: Healthy physiology is characterized by fractal regulation (FR) that generates similar structures in the fluctuations of physiological outputs at different time scales. Perturbed FR is associated with aging and age-related pathological conditions. Shift work, involving repeated and chronic exposure to misaligned environmental and behavioral cycles, disrupts circadian coordination. We tested whether night shifts perturb FR in motor activity and whether night shifts affect FR in chronic shift workers and non-shift workers differently.

METHODS: We studied 13 chronic shift workers and 14 non-shift workers as controls using both field and in-laboratory experiments. In the in-laboratory study, simulated night shifts were used to induce a misalignment between the endogenous circadian pacemaker and the sleep-wake cycles (ie, circadian misalignment) while environmental conditions and food intake were controlled.

RESULTS: In the field study, we found that FR was robust in controls but broke down in shift workers during night shifts, leading to more random activity fluctuations as observed in patients with dementia. The night shift effect was present even 2 days after ending night shifts. The in-laboratory study confirmed that night shifts perturbed FR in chronic shift workers and showed that FR in controls was more resilience to the circadian misalignment. Moreover, FR during real and simulated night shifts was more perturbed in those who started shift work at older ages.

CONCLUSIONS: Chronic shift work causes night shift intolerance, which is probably linked to the degraded plasticity of the circadian control system.

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Reduced Tolerance to Night Shift in Chronic Shift Workers: Insight From Fractal Regulation

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