The Relationship Between the Circadian Rhythm and Parkinson's and Alzheimer's

 The circadian rhythm can be described as oscillations that have about a 24 hour cycle. The suprachiasmatic nucleus, or SCN, is responsible for organizing the circadian rhythm in both physiology and behavior. The circadian rhythm is regulated by the SCN, behavioral factors, and environmental factors (Fishbein, et al., 2021). The disruption of the circadian rhythm by any factor can result in poor health, both mentally and physically (Fishbein, et al., 2021). A large number of people are at risk for disruption of their circadian rhythm including night shift workers, those who work indoors, and the majority of the population that is affected by light pollution (Fishbein, et al., 2021). Shen, et al. further discusses the relationship between circadian rhythm and neurodegenerative disorders, specifically Parkinson’s disease (PD) and Alzheimer's disease (AD).

Shen, et al. discuss that “dysregulated circadian rhythm and sleep could predispose disease onset and exacerbate disease progression” (Shen, et al., 2023). They focus on studying specifically how dysregulation of the circadian rhythm relates to PD and AD. Shen, et al. define PD as a blend of motor and nonmotor disorders. They classify the disruption of the circadian rhythm in PD in three ways: behavioral, physiologic, and molecular alterations. In PD, the circadian rhythm disruption is “characterized by a reduction in the amplitude of the circadian rhythm”, meaning there is not a shift in circadian rhythm phases (Shen, et al., 2023). Shen, et al. studied patients with PD that reported excessive daytime sleepiness (EDS) and those who did not. It was found that patients with PD that reported EDS had significantly lower amplitudes of the melatonin rhythm (Shen, et al., 2023). Studies have found that those who have reported EDS “have a twofold risk of developing PD” (Shen, et al., 2023). In relation to AD, rest-activity rhythm is a common indicator of circadian disruption. Patients with AD have been found to have an increased fragmentation in rest-activity rhythm as well as a decrease in daytime activity (Shen, et al., 2023). More studies need to be done in regards to circadian amplitude. Lastly, researchers noticed that greater sleep efficiency was associated with a decrease in AD risk (Shen, et al., 2023).

In regards to Parkinson’s disease, the findings described above indicate that it is possible that circadian rhythm disruption is a preliminary marker for PD. In regards to Alzheimer's disease, the above finding supports the idea that those with circadian rhythm disruption are at a higher risk for developing AD. Through the work done by Shen, et al. it can clearly be seen the toll that the disruption of the circadian rhythm can take on one’s health, as described by Fishbein, et al. Fishbein, et al. also discuss the population of people that are at risk for circadian rhythm disruption, including night shift workers and those who work indoors. With the work done by Shen, et al. more studies can be done to see if there are correlations between PD and AD in night shift workers and those who work indoors.

References: 

Fishbein, A. B., Knutson, K. L., & Zee, P. C. (2021, October 1). Circadian Disruption and human health. The Journal of Clinical Investigation. Retrieved from https://www.jci.org/articles/view/148286#version_history  

Shen Y, Lv QK, Xie WY, Gong SY, Zhuang S, Liu JY, Mao CJ, Liu CF. Circadian disruption and sleep disorders in neurodegeneration. Transl Neurodegener. 2023 Feb 13;12(1):8. doi: 10.1186/s40035-023-00340-6. PMID: 36782262; PMCID: PMC9926748.