A recent review article posted in the Nature journal Translation Psychiatry detailed how researchers at the University of California (UoC), Irvine, have suggested that circadian rhythm disruption (CRD) is associated with many mental health disorders.
What are circadian rhythms, and how can they be disrupted?
Circadian rhythms are dynamic patterns that regulate internal processes in a 24-hour (solar) day. They function in a diurnal pattern in response to light input reaching the suprachiasmatic nucleus, a tiny region in the brain that acts as a master clock and central pacemaker. Among other functions, circadian rhythms regulate the sleep-wake cycle and hormonal release. Think about how you often feel a dip around midday (or maybe 3pm) - that’s caused by the fluctuating patterns in your circadian cycle. When there is an interruption along the signal transduction pathway, however, for example during the amplification of a light or dark input entering from the eye, the rhythm is disrupted. This can be caused by behavioural patterns, such as changing your sleep schedule or too much blue light from a device, but also by genetic mutations to the clock genes involved in regulating our circadian rhythms. CRD can lead to many disorders such as disordered cognition, as seen in sundown syndrome, or sleep dysfunction disorders such as Insomnia.
"Sleep deprivation not only results in negative side effects such as cognitive dysfunction but also shifts the circadian cycle"
Circadian rhythm disruption and sleep disorders
However, that’s not all, as CRD has also been linked to mental health. According to the authors, “CRD is a common underlying p-factor that bridges across mental disorders”, highlighting that it could be a common ground amongst many mental health disorders, despite the differences in their presenting symptoms. To further investigate this, the researchers reviewed multiple sources in the literature that state abnormal sleep as a common factor contributing to disruption. Sleep deprivation not only results in a plethora of negative side effects, such as cognitive dysfunction but also shifts the circadian cycle, forcing the individual to perform daily routines outside of their typical rhythm. Moreover, there is a vicious cycle between stress and sleep; the less we sleep, the more stressed we are, and the more stressed we are, the less we sleep. This may lead to the development of stress-related mental health disorders.
Circadian rhythm disruption and neurodevelopment
Neurodevelopmental disorders are a group of mental health disorders that affect the development of the nervous system, including ADHD, Tourette’s syndrome, schizophrenia, and autism spectrum disorder. The authors investigate a genetic link involving CRD and its heritability, leading to neurodevelopmental disorders. To demonstrate shared CRD amongst mental disorders, the researchers at the UoC discuss an experiment concerning pregnant mice. These mice were exposed to CRD via a maternal stressor - dysregulation of melatonin production - much like the ones faced by most women during pregnancy. Melatonin is a hormone released from the brain at night and is commonly used to treat sleep and psychiatric disorders. The offspring of affected mice displayed behaviours such as social avoidance and hyperactivity, alongside molecular changes to the functionality of the suprachiasmatic nucleus. These two behaviours are often associated with ADHD and generalised anxiety disorder. The offspring also displayed increased production of adrenal cortisol, a stress-related hormone. This may suggest that stress caused by CRD during pregnancy can predispose offspring to such disorders.
Further work and implications
Although this study identifies a link between CRD and mental health, the underlying question, “Is CRD causative, or does it develop due to predefined mental health disorders?”, remains. The researchers at UoC suggest further work to answer this, such as an investigation of CRD at a molecular level on a large-scale animal model via gene transcription. In future, studies in this field could help scientists predict gene biomarkers for these conditions and develop novel approaches to manage mental health.
This article was written by Rebecca Parker and edited by Julia Dabrowska. Interested in writing for WiN UK yourself? Contact us through the blog page and the editors will be in touch!
Interesting! I often have that post-lunch dip but never knew circadian cycles could be contributing to that. Thanks for the insights @Rebecca Parker