Sleep and circadian rhythms are inherently connected in many species, and the proper function of these rhythms is extremely important for proper sleep and development in humans. With the rise of current electronic technology and blue-light screens on mobile devices, light pollution is not the only unnatural light that people face on a day-to-day basis. Light levels, specifically dim and low-level light during the night have been thought to be some of the main contributors to these disruptions. Besides symptoms like chronic sleep deprivation and poor sleep quality, various neurological conditions or disorders have been correlated with chronic circadian disruptions as well. Among the many conditions, mood disorders have been highlighted concerning the relationship between depressive symptoms and light exposure. Both articles in this review studied the connection between circadian rhythm disruptions and the drastic effects on human health for mood disorders.
"Circadian disruption and human health" by Zee et al., studied the interactions of circadian rhythm disruptions and many conditions, some of which were neurological mood disorders. Analysis of the data presented insists that there is a clear linkage between sleep disruption and these disorders, through various methods and ways. Manipulation of serotonin receptors had been shown to be a circadian disrupter; when the light was shown at inappropriate times, signs of depression were induced in mouse models. Similar functions with human fMRI scans showed suppression of the amygdala with the same conditions; relations to improved connectivity of the prefrontal cortex show a possible connection between light and mood. Melatonin suppression is shown to play a part in these disruptions as well, like in studying the delayed sleep-wake phase disorder (DSWPD) where misalignment of on-set melatonin release causes increased signs of depressive symptoms. When concerned with aligning melatonin release and showing light at appropriate times, it had been shown to lower depressive symptoms, while in turn decreasing circadian disruptions.
In "Circadian rhythm disruption and mental health" by Nelson et al., Nelson studied the effects of specific mood disorders, some of which were also discussed in Zee's article. Their focus centered on analyzing Bipolar Disorder (BD), Schizophrenia (SZ), Anxiety, and Major Depression Disorder (MDD), all of which have diagnostic criteria related to sleep disruption. For MDD, the symptoms of MDD in night-time shift workers were analyzed concerning individuals' circadian disruptions, compared to day-shift workers in South Korea. It was shown that night-shift workers were significantly more likely to suffer from MDD symptoms due to the circadian disruptions of light exposure while working at night. An accumulation of 11 replica studies found that on average night-shift workers were 40% more likely to suffer from depressive symptoms of MDD, showing evidence that circadian disruptions might play a role. Other mood disorders show similar results concerning their individual symptoms and how circadian disruptions can exacerbate those symptoms. For Anxiety, environmental circadian disrupters were shown to have an impact on anxiety-related behavior. For SZ, the severity of symptoms has been shown to be directly related to the number of circadian disrupters. Having circadian disrupters across the board tends to make symptoms more severe or more likely to happen in mood disorders.
In conclusion, both of these articles highlight important and similar findings when concerning the consequences of chronic circadian rhythm disruptions and levels of symptoms in mood disorders. More studies replicating these findings could lead to possible treatments, and help manage a patient's severity of symptoms for sometimes life-debilitating conditions.
References:
Fishbein, A. B., Knutson, K. L, & Zee, P. C. (2021) Circadian disruption and human health. J Clin
Invest. 2021;131(19):e148286. https://doi.org/10.1172/JCI148286.
Walker, W.H., Walton, J. C., DeVries, A. C., & Nelson, R. J., Circadian rhythm disruption and mental
health. Transl Psychiatry 10, 28 (2020) https://doi.org/10.1038/s41398-020-0694-0
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