Circadian disruption: What do we actually mean?

Abstract

The circadian system regulates physiology and behavior. Acute challenges to the system, such as those experienced when traveling across time zones, will eventually result in re‐synchronization to local environmental time cues, but this re‐synchronization is oftentimes accompanied by adverse short‐term consequences. When such challenges are experienced chronically, adaptation may not be achieved, as for example in the case of rotating night shift workers. The transient and chronic disturbance of the circadian system is most frequently referred to as “circadian disruption”, but many other terms have been proposed and used to refer to similar situations. It is now beyond doubt that the circadian system contributes to health and disease, emphasizing the need for clear terminology when describing challenges to the circadian system and their consequences. The goal of this review is to provide an overview of the terms used to describe disruption of the circadian system, discuss proposed quantifications of disruption in experimental and observational settings with a focus on human research, and highlight limitations and challenges of currently available tools. For circadian research to advance as a translational science, clear, operationalizable, and scalable quantifications of circadian disruption are key, as they will enable improved assessment and reproducibility of results, ideally ranging from mechanistic settings, including animal research, to large‐scale randomized clinical trials.

Chronic circadian misalignment accelerates immune senescence and abbreviates lifespan in mice

“…Comprehensive analysis of the long-term circadian misalignment-conditioned peripheral organs. The failure of tuning the peripheral clocks via the autonomic nervous system and/or endocrine system, as a result of SCN desynchronization, has been shown to initiate various systemic physiological dysfunctions 2,26,27 . The liver is a central peripheral organ whose functions are regulated by the circadian system 26 .…”

“…For example, circadian rhythms are closely linked with the sympathetic activity rhythm, and its dysregulation modulates immune functions [47][48][49][50] . In addition, endocrine dysregulation, often induced by jet-lag 2,26,27 , has been shown to be associated with immune senescence 51 . Moreover, since jet-lag induces dysbiosis in both mice and humans 52 , modification of gut microbiota may also contribute to the acceleration of immune senescence 53 .…”

Chronotype and Social Jetlag - a (self-)critical review

“…As such, we envisioned SJL as a measure of circadian misalignment. Circadian misalignment is described as an abnormal phase angle difference between two or more rhythms, be they just internal or both internal and external (reviewed by Vetter et al 2018 [62]). If the Body Clock of a late chronotype is stably entrained to a late phase in the light-dark cycle despite having to get up with an alarm clock five days a week, one can presume a misalignment between body clock and social schedules.…”

Circadian rhythmicity and the community of clockworkers

“…Strategies for reducing circadian misalignment‐induced risk include targeting light/dark exposure, napping, physical activity, and meal timing. However, there is much variation in what researchers consider to be ‘circadian disruption’ as well as how this disruption should be experimentally measured in laboratory and field studies (Vetter, ). Chronobiologists must improve precision in the term ‘circadian disruption’.…”