The circadian rhythm is like humans’ biological internal clock. It dictates biological cues on a daily cycle. The circadian rhythm is influenced by the environment, particularly light and darkness. This is why people tend to feel sleepy or wake up around the same time every day. However, this biological feature is not exempt for flaws. Some people suffer from circadian rhythm disorders, causing the biological clock to malfunction. There are several kinds of circadian rhythm disorders (CRDs). These disorders include jet lag, shift work sleep disorder, delayed sleep phase disorder, advanced sleep phase disorder, irregular sleep-wake rhythm disorder, and non-24-hour sleep-wake disorder. (National Institute of General Medical Sciences), (WebMD)
(National Center for Biotechnology Information), (American Academy of Sleep Medicine), (Sleep Foundation),
(National Organization for Rare Disorders), (Society for Endocrinology)
Although the association between jet lag disorder and age is still unclear, older people seem to be more likely to not only experience JLD but also have worse symptoms.
(National Association of Managed Care Physicians)
Social jetlag the time difference between the midpoint of sleep on workdays and on free days. If someone sleeps from 9 PM to 5 AM on workdays, his midpoint of sleep is 1 AM. If he sleeps from 12 MN to 8 AM on free days, his midpoint of sleep is 4 AM. This gives him a 3-hour SJL.
(National Center for Biotechnology Information)
The researchers further found that people below 61 years old with SJL have higher blood glucose levels, higher waist circumference.
(National Center for Biotechnology Information)
Not only did the people with SJL have higher fat mass and larger waist circumference, but they also had higher markers for inflammation and diabetes.
(Dr. MJ Parsons)
Besides being more prone to depression, the participants with SJL were also younger, more likely to be female, in a low-ranking job position, blue-collar workers, and smokers. They were also less likely to be married and consumed less vitamins.
(Oxford Academic)
People with SJL also generally ate more calories at dinner, more protein at lunch. They also had longer eating durations.
(Maria Carliana Mota affiliation Faculty of Medicine of the Federal University of Uberlândia, Minas Gerais, Brazil)
This same study also found that people with SJL also had poorer health, worse mood, and higher sleepiness and fatigue.
(Science Daily)
Shift work sleep disorder is common in people working outside the usual 8 or 9 to 5 job. SWSD is chronic causes excessive sleepiness, insomnia, unrefreshing sleep, difficulty in concentrating, low energy, and mood abnormalities such as depression.
(Christopher Drake, PhD), (National Sleep Foundation)
This same study found that rotation shift workers with SWSD are more than 4 times more likely to have ulcers. Rotating workers also more frequently missed work.
(Christopher Drake, PhD)
This often happened after every fourth night shift. Moreover, the risk for a drowsy driving episode doubled when nurses worked 12.5 or more consecutive hours
(Linda Scott, PhD)
This same study also found that these medical residents were nearly 6 times more likely to have near-miss incidents.
(Laura K. Barger, PhD)
These workers also had a 5% higher risk of hypertension. Moreover, these workers had higher fasting blood glucose and average blood pressure. They also poorer sleep quality.
(National Center for Biotechnology Information)
This was a 24-year study that was done with nearly 200,000 participants. Quitting from shift work reduced the chances of CHD.
(Céline Vetter, PhD)
People with delayed sleep phase disorder have a sleep pattern that is “delayed” by 2 or more hours. This delay happens when the circadian rhythm shifts later at night and later in the morning. People with DSPD may prefer late bedtimes and late wake-up times.
(Sleep Education)
This study found the most common mood disorder was major depressive disorder. This study also found that many of the participants were also diagnosed with alcohol or substance abuse.
(Kathryn J. Reid, PhD)
As the name suggests, people with advanced sleep phase disorder sleep at earlier times. These people also tend to naturally wake up between 2 and 5 AM. Thus, people with ASPD have a circadian rhythm that is ahead by a few hours.
(Sleep Education)
Since most people do not look down upon asleep and waking up earlier, in contrast to sleeping and waking up later, the prevalence of ASPD may be underestimated. ASPD also seems to affect males and females equally.
(Sleep Health Foundation), (Dr. Robert L. Sack), (Lirong Zhu MD, PhD)
This prevalence makes people think there may be a genetic factor in ASPD. Some researchers now link ASPD to mutations in the genes hPer2 and CSK1D, which are known as the clock genes of the human body.
(Dr. Robert L. Sack), (Lirong Zhu MD, PhD)
Normal people tend to fall asleep and wake up around the same time. However, people with ISWRD have a disorganized sleep and wake times that have no clear pattern.
(Phyllis C. Zee, MD, PhD and Michael V. Vitiello, PhD)
These bouts of sleep are spread throughout the day and may not occur at regular intervals. However, the total amount of sleep is normal for the age of the afflicted persons.
(Phyllis C. Zee, MD, PhD and Michael V. Vitiello, PhD)
Moreover, people with ISWRD daily periods of agitation and wandering, often in the evening, which is colloquially known as sundowning. This feature may actually be a sign of a dysfunctional cerebral cortex.
Daniel R. Wagner MD)
Nonetheless, age itself is not an independent risk factor. The high prevalence with age is secondary to the high prevalence of associated medical disorders with increased age.
(Phyllis C. Zee, MD, PhD and Michael V. Vitiello, PhD)
In N24, sleep and wake up times continue to move later and later every day. An external light-dark cycle stimulates normal people’s circadian rhythm resets every 24 hours. However, in N24, the body does not respond to this stimulus. This is the reason why N24 is prevalent in the blind.
(Sleep Education)
Diagnosis of N24 is difficult because it can be easily confused with other circadian rhythm disorders, such as delayed sleep phase disorder. A key difference, though, between N24 and DSPD is the progressive sleep delay in N24. People with N24 can initially fall asleep in the morning, which further shifts to the afternoon, and then eventually further shifting to night.
(Dr. Maria Antonia QUERA SALVA), (National Organization for Rare Disorders)
Although rare, N24 also occurs in those with sight. Factors that may cause N24 in sighted people include reduced or heightened response the internal body clock to light, reduced or untimely environmental or social cues, or genetics.
(National Organization for Rare Disorders)
Healthy adults show that on males have longer circadian periods than women, However, because of the extremely low number of known N24 cases in sighted people, this 4:1 ratio is a weak indication that males are more pre-disposed to N24.
(National Organization for Rare Disorders)
Diseases with higher prevalence and mortalities have the attention of most clinical trials. Thus, there are few medications or therapy procedures of circadian rhythm disorders.
(National Center for Biotechnology Information)
Behavioral therapy includes chronotherapy, bright light therapy, and enhancing environmental cues. These are often done in combination with sleep-promoting compounds such as melatonin.
(Ehren R. Dodson, PhD and Phyllis C. Zee, MD, PhD)
The circadian rhythm is a crucial part of human biology. Although it may be brushed off by those safe from circadian rhythm disorders, those who have these disorders can severely suffer. The small attention on circadian rhythm disorders should prompt anyone with possible symptoms to consult the few people who specialize in these ailments.
National Institute of General Medical Sciences:
https://www.nigms.nih.gov/education/pages/factsheet_circadianrhythms.aspx
WebMD:
https://www.webmd.com/sleep-disorders/circadian-rhythm-disorders-cause#1
Kim et al., 2014:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4212693/
Schrader et al., 1993:
https://pubmed.ncbi.nlm.nih.gov/10607071/
American Academy of Sleep Medicine:
https://aasm.org/resources/factsheets/crsd.pdf
Sleep Foundation:
National Organization for Rare Disorders:
https://rarediseases.org/rare-diseases/non-24-hour-sleep-wake-disorder/
Society for Endocrinology:
https://www.yourhormones.info/endocrine-conditions/jet-lag/
National Association of Managed Care Physicians:
http://www.namcp.org/sleepdisorders/html/disorders/jetlag/epidemiology.html
Koopman et al., 2017:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5564947/
Islam et al., 2020:
https://academic.oup.com/sleep/article/43/1/zsz204/5573922
Mota et al., 2019:
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0212126
ScienceDaily:
https://www.sciencedaily.com/releases/2017/06/170605085326.htm
Parsons et al., 2015:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4422765/
Drake et al., 2004:
https://pubmed.ncbi.nlm.nih.gov/15683134
Scott et al., 2007:
https://pubmed.ncbi.nlm.nih.gov/18246989/
Barger et al., 2005:
https://pubmed.ncbi.nlm.nih.gov/15647575/
Guo et al., 2013:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3745433/
Vetter et al., 2016:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5102147/
Sleep Education:
Reid et al., 2013:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3474860/
Sleep Education:
Sack et al., 2007:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2082099/
Zhu et al., 2012:
https://www.sciencedirect.com/science/article/pii/S0733861912000527?via%3Dihub
Zee and Vitiello, 2010:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2768129/
Sleep Education:
Salva et al., 2017:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5741691/
National Organization for Rare Disorders:
https://rarediseases.org/rare-diseases/non-24-hour-sleep-wake-disorder/
Selfridge et al., 2016:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5082589/
Dodson and Zee., 2011:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3020104/
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