Don’t disturb your rhythm! Health impact of shift work and social jetlag

Astrid Streng

Research output: Types of ThesisDoctoral ThesisInternal

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Abstract

It is unclear to what extent our current 24/7 economy and the associated disturbance of our day and night rhythm contribute to the development of serious adverse health effects later in life. In this thesis, we investigate the effect of day-night rhythm disturbance, especially shift work and social jetlag. A social jetlag is the discrepancy between the social and biological rhythm, this is caused by a different sleeping rhythm during the working days and days off. Because effects of circadian disturbance, exposure to light and other exposure-related factors during the night are almost impossible to separate in human studies, we use laboratory animals. In our studies, we used specially designed cages with timed sleep restriction to further investigate circadian disturbance, such as social jet lag and night shift work. We showed that timed restricted sleep protocols are effective in disturbing normal activity and sleep patterns. Here, we showed that timed sleep restriction cages can be used to create a social jetlag. In addition, we did a sleep analysis looking at Cry-deficient mice that were expected to have a different chronotype than normal Wildtype mice. A person's chronotype determines a person's natural tendency to go to sleep and be awake. Our data confirmed that the Cry1-deficient mouse is a suitable model for a human early chronotype, i.e. it mimics a morning person. We used timed sleep restriction cages to study rotating shifts and the effect on breast cancer latency. No effects were observed on body weight gain and latency to breast cancer development. The effect of night shift and social jetlag on mutation frequency and tumor formation in mice was also investigated. We showed that forced awakening during the early morning or night does not lead to a higher tumor incidence nor to a shorter latency time (although a trend was observed in the night shift group). Mice exposed to the night work schedule showed hair thinning and gray hair, lower skeletal muscle strength, lower body weight and higher food intake. We also did an epidemiological study in which we looked at the differences in metabolic risk factors and immune cell profiles between day and night workers in a Dutch cohort. Our study showed that the risk factors appear to be particularly elevated in night shift workers with a higher frequency of night shifts (≥5 night shifts per month) and more consecutive night shifts (>3 consecutive night shifts), while these associations were less pronounced in long-term night shift workers (≥20 year).
In summary, the work presented in this thesis has contributed to a valuable model to further investigate circadian rhythm disturbances caused by sleep restriction in animal studies. In addition, this thesis provides new insights into circadian rhythm disturbances, in particular the effect of sleep restriction during night shifts and social jetlag on health.
Original languageEnglish
Awarding Institution
  • Erasmus University Rotterdam
Supervisors/Advisors
  • van der Horst, Bert, Supervisor
  • Machado, Ines, Co-supervisor
  • van Kerkhof, LWM, Co-supervisor, External person
Award date13 Apr 2023
Place of PublicationRotterdam
Publication statusPublished - 13 Apr 2023

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