It may seem like the easiest and most effortless thing, but falling asleep involves a lot more than just closing your eyes and resting your head on a pillow. Catching some z's requires a harmony between our body's internal systems and our external environment. Our body's internal systems work at a molecular level and fluctuate throughout the day. The internal factors are primarily composed of an interplay of hormones such as cortisol and melatonin. The external or environmental factors consist of light, temperature, and sound as well as behavioral factors such as feeding and activity. Circadian disruption occurs when there is a hindrance to the body's biological timing. This can occur at the molecular level with disturbances to rhythms in cells, or it can be attributed to the misalignment of behavioral patterns with environmental changes. The balance between our body's internal systems and external environment is processed in the suprachiasmatic nucleus located in the hypothalamus. The suprachiasmatic nucleus is referred to as the "master clock" as it regulates most of the body's circadian rhythms. It is important to note that the SCN initiates a 24 hour rhythm that is synchronized to exposure to sunlight. When light reaches the retina, the optic nerve delivers the light signal to the SCN which then activates the pineal gland, which is responsible for secreting melatonin. Melatonin is a hormone produced in response to darkness which regulates the body's internal clock. Being exposed to light at night can hinder melatonin production, thus disturbing the body's circadian rhythm.
Why is sleep so important? Getting good quality sleep improves health and brain function as well as mood. In the Article titled Circadian disruption and human health by Phyllis C. Zee, the impact of disrupted circadian rhythms on cardio-metabolic as well as neuropsychiatric disorders is discussed. It is noted that circadian disruption occurs at multiple organizational levels and involves a bidirectional relationship. This implies that disruption in circadian rhythms can increase the severity of a disease, while it is also possible that certain diseases impair the body's circadian rhythm. The article states that when circadian rhythms are disrupted, it can have serious repercussions on mental as well as physical health. The possible negative implications of circadian disruption include but are not limited to sleep-wake disorders, psychiatric disorders, neurological disorders, metabolic disorders, and cardiovascular disorders.
We have discussed why getting good sleep is important, as well as how harmful circadian disruption can be for mental and physical health. We have also discussed how our body's 24 hour circadian rhythms are closely synchronized with light exposure, meaning the proper timing and duration of exposure to light is critical in ensuring a good quality sleep. If we know that exposure to light during the day and darkness at night is what our body's need to get good sleep, what happens if you live somewhere where there are months of darkness followed by months of constant sunlight?
The article titled An exploratory study examining the associations between sunlight exposure, sleep behaviours and sleep outcomes during an Arctic summer by Margaret M. Lubas tackles this exact question. This article aims to investigate the relationship between light exposure, sleep outcomes, and living in the Arctic. This article states that being exposed to light in the late afternoon can set back the internal clock, while exposure to light in the morning can boost circadian rhythms. Considering the importance of light as a regulatory factor in the circadian system, living in an environment that undergoes extreme changes in day length depending on the season presents an impediment to the body's circadian rhythm. The findings of the study presented in this article indicated a high occurrence of poor sleep, an increase in sleep onset latency, and prevalent use of sleeping aids among the sample of Arctic workers throughout the period of increased sunlight during the summer. Based on the daily measures collected, the study suggested that as the length of daylight exposure increased, poor sleep quality simultaneously increased, while sleep duration also decreased. These findings support previous studies regarding sleep disturbances in the Arctic.
Considering the findings of this study on the Arctic as well as what we know about the importance of proper daylight exposure for regulating the body's circadian rhythm, additional evidence-based interventions would be beneficial in improving sleep quality for those who live in the Arctic.
References:
Fishbein, Anna B., et al. “Circadian Disruption and Human Health.” Journal of Clinical Investigation, vol. 131, no. 19, 2021, https://doi.org/10.1172/jci148286.
Lubas, Margaret M., et al. “An Exploratory Study Examining the Associations between Sunlight Exposure, Sleep Behaviours and Sleep Outcomes during an Arctic Summer.” International Journal of Circumpolar Health, vol. 78, no. 1, 2019, p. 1574698., https://doi.org/10.1080/22423982.2019.1574698.
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