by Nandita Jena
Credits: MedFriendly.com
Sleep is an essential bodily process that differs hugely among individuals, influenced by both genetic and environmental factors. Research shows that while on average, an adult needs between 7-9 hours of sleep per night, some individuals may function best with slightly more or less sleep.[1] Recognising individual sleep patterns involves considering chronotype, which categorises individuals based on their preference for waking hours. While ‘owls’ prefer to stay up later into the night and have difficulty waking up earlier in the morning, ‘larks’ are people who naturally wake up early and feel most alert in the morning. These preferences are partly determined by genetics but may also be influenced by environmental factors and age.
Sleep-wake cycles are controlled by the circadian system, an intricate network of biological clocks in the brain's suprachiasmatic nucleus which regulate other physiological processes such as body temperature and hormone release. The timing of these internal clocks is crucial for maintaining good health and well-being. Personal differences in circadian rhythm timing can be caused by genetic variations affecting the speed of the circadian clock. A slower circadian clock may lead to a preference for evening alertness (owls), but some people (larks) may have a circadian clock that runs faster than 24 hours, which causes them to prefer morning wakefulness.
Disruptions in circadian rhythm regulation, whether due to genetic mutations or environmental factors like shift work or jet lag, can have large effects on health and behaviour. Studies in mice have shown that altering circadian clock genes can lead to detrimental outcomes, including disruptions in mood, cognition, and metabolism. [2] Additionally, mutations in specific internal clock genes can result in extreme sleep phase disorders. Advanced sleep phase syndrome (ASPS) is characterised by a very early bedtime and wake time, often resulting in chronic sleep deprivation. Alternatively, delayed sleep phase syndrome (DSPS) involves difficulty falling asleep and waking up early, leading to challenges in meeting social and work obligations.
Treatment for these sleep phase disorders aims to reset the internal circadian clock. Light therapy, involving exposure to specific wavelengths of light at strategic times, can help adjust circadian rhythms to align more closely with desired sleep-wake schedules. Exposure to certain wavelengths of light, such as blue light from screens, can inhibit the production of the hormone melatonin in the pineal gland, keeping a person awake, whereas warm lighting stimulates melatonin production, increasing drowsiness. Future research aimed at understanding the genetics of the biological clock will also further develop treatment options for individuals with genetic sleep disorders.
Citations
[1] Chaput, J.-P., Dutil, C. and Sampasa-Kanyinga, H. (2018) ‘Sleeping hours: What is the ideal number and how does age impact this?’, Nature and Science of Sleep, Volume 10, pp. 421–430. doi:10.2147/nss.s163071.
[2] Imamura, K. and Takumi, T. (2022) ‘Mood phenotypes in rodent models with circadian disturbances’, Neurobiology of Sleep and Circadian Rhythms, 13, p. 100083. doi:10.1016/j.nbscr.2022.100083.
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