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"The circadian rhythm is a fundamental mechanism that regulates the body's biological clock and directly impacts our health."
Title:
| What is the circadian rhythm?
| What happens when your circadian rhythm is disrupted?
| What is circadian rhythm-related sleep disorders?
| Delayed sleep phase disorder (DSP)
| Advanced sleep phase disorder (ASP)
| Irregular sleep-wake rhythm disorder
| Non-24-hour sleep-wake rhythm disorder
| Jet lag disorder
| Shift work disorder
| How are circadian rhythm sleep-wake disorders diagnosed?
| Who is at risk for circadian rhythm sleep disorders?
| How can we fix the circadian rhythm?
| How can we prevent circadian rhythm disorders?
| Summary
What is the circadian rhythm?
Circadian rhythms are biological rhythms generated by our body. “Circadian” means about a day, and circadian rhythm is defined as rhythmic changes in biological processes that occur within approximately 24 hours. Circadian clock adapted to track the Earth's daily rotation, enabling organisms to predict sunrise, establish consistent sleep-wake cycles, and efficiently manage metabolic needs. This timekeeping mechanism is preserved in humans, with nearly every organ and cell synchronized to the 24-hour cycle. This synchronization optimizes energy production during the activity span and supports energy conservation, cellular repair, and restoration during rest periods. Circadian rhythms are generated and coordinated by the central clock (suprachiasmatic nuclei (SCN), located in the brain. Every day, environmental cues such as the light-dark cycle, meal timing, work schedules, and social interactions adjust the circadian rhythms to the 24-hour. Light is the primary signal for synchronizing the circadian clock, detected by photoreceptors in the eye and transmitted to the brain through retinal ganglion cells.
What happens when your circadian rhythm is disrupted?
Circadian rhythm disruptions are linked to a wide range of health issues. When disrupted, the circadian rhythm can contribute to or exacerbate various conditions, including sleep disorders, cardiovascular disease, metabolic disorders such as diabetes and obesity, cancer, neurological diseases, and psychiatric conditions like major depressive disorder (MDD) and bipolar disorder (BD). Among these, sleep disorders are some of the most extensively studied and closely linked to circadian rhythm disruptions. While partially influenced by personal choices, the circadian clock is the main factor regulating sleep timing, length, and pattern. Adequate sleep is crucial for maintaining physiological functions, enhancing cognitive performance, and supporting emotional well-being, all of which are essential for overall health.
What is circadian rhythm-related sleep disorders?
Circadian rhythm sleep-wake disorders, as defined by the International Classification of Sleep Disorders, involve chronic or recurring disruptions in sleep-wake patterns caused by misalignment between the internal circadian clock and external schedules. These disruptions can cause sleep to occur too early, too late, to shift daily, or to lack a consistent pattern, and they are classified as specific types of circadian sleep disorders. Such disorders interfere with preferred sleep times, social activities, and work schedules, making it difficult to maintain a healthy sleep-wake cycle.
Delayed sleep phase disorder (DSP)
Delayed Sleep Phase (DSP) disorder is a circadian rhythm sleep disorder where a person's sleep-wake cycle is significantly delayed compared to the typical schedule. Individuals with DSP often go to bed and wake up much later than what is considered normal, preferring late-night activities and late-morning or afternoon wake-ups. Despite the delay, their sleep quality and duration are normal when aligned with their natural schedule. DSP is more common among adolescents and young adults, with a high number of cases showing a positive family history.
Advanced sleep phase disorder (ASP)
People with Advanced Sleep Phase (ASP) disorder have a sleep-wake cycle that is shifted earlier than normal. Those with ASP, often described as "morning types," generally go to bed between 6 p.m. and 9 p.m. and wake up between 2 a.m. and 5 a.m. Their sleep pattern remains consistent when they can stick to their preferred early schedule. ASP is more common in middle-aged and older adults, with its prevalence increasing with age.
Irregular sleep-wake rhythm disorder
Irregular sleep-wake rhythm disorder is characterized by a divided and inconsistent/irregular sleep-wake cycle, with sleep broken into multiple naps throughout a 24-hour period. Affected individuals are typically unable to experience a single, uninterrupted sleep episode. This disorder is most commonly observed in individuals with neuropsychiatric conditions, including schizophrenia, Alzheimer’s disease, and autism spectrum disorder.
Non-24-hour sleep-wake rhythm disorder
This disorder involves a progressively shifting sleep-wake cycle, with sleep times occurring later each day. It often arises when the brain lacks light environmental cues, commonly affecting blind people, as the circadian clock relies on the light-dark cycle for regulation.
Jet lag disorder
Jet lag arises from long-distance travel to a destination in a different time zone, causing the brain's internal clock to fall out of sync with the new environment. This misalignment with the light/dark cycle leads to symptoms such as daytime fatigue, mood changes, headaches, difficulty concentrating, and digestive problems. Jet lag typically begins within one to two days of crossing two or more time zones and generally takes about one day per hour of time difference to adjust fully. The severity of symptoms increases with the number of time zones crossed, and adjusting to eastward travel is generally more challenging than westward travel. All ages can be affected by jet lag, however elderly individuals frequently have more severe symptoms and recover more slowly than younger people.
Shift work disorder
Shift work disorder arises when work hours overlap with the normal sleep period, leading to sleepiness during shifts and difficulty sleeping during the day. Adaptation to shift work varies based on circadian preferences, with individuals who naturally prefer morning activity often obtaining less daytime sleep after night shifts. Those with medical or psychiatric conditions, sleep disorders like sleep apnea, or a strong need for consistent sleep schedules may be at higher risk. Chronic shift workers, whether on rotating schedules or consistent night shifts, are also at increased risk for a range of health issues, including psychiatric disorders such as depression.
How are circadian rhythm sleep-wake disorders diagnosed?
The following criteria are used for diagnosing circadian rhythm sleep disorders:
A persistent or repeated alteration in the sleep-wake cycle caused by the circadian clock or misalignment with planned or necessary schedules.
The presence of sleep-related issues, like excessive daytime sleepiness, insomnia, or both.
Disruption in daily functioning that significantly affects routines, including social or professional activities.
Note: Symptoms must persist for at least 3 months, and the condition should not be attributed to other sleep disorders or psychiatric problems. Jetlag disorder is excluded from this 3-month requirement.
Who is at risk for circadian rhythm sleep disorders?
Reasons causing circadian sleep disorders include both internal and external factors. The following factors may increase the risk of developing a circadian rhythm disorder.
Genetics: Polymorphisms or mutations of some genes regulating the circadian clock can affect circadian rhythms and cause sleep disorders.
Chronotypes: Certain chronotypes are more prone to specific circadian rhythm sleep disorders. For example, evening chronotypes, who naturally wake up and go to sleep late, are more likely to develop delayed sleep phase disorder than morning chronotypes.
Neuropsychiatric disorders, including brain injury, mood disorders, schizophrenia, Parkinson’s disease, and dementia
Working overnight shifts
Frequent travel across time zones
How can we fix the circadian rhythm?
Lifestyle changes:
Establish and maintain a consistent daily routine.
Spend time outdoors during daylight hours to enhance wakefulness and regulate your internal clock.
Avoid consuming caffeine, nicotine, and alcohol, particularly in the evening.
Limit exposure to artificial light, including light from screens, a few hours before bedtime, as blue light from electronic devices can prevent you from falling asleep.
Treatments:
Treatment options for circadian rhythm disorders depend on the specific type of the disorder and underlying causes and may include light therapy or medications such as melatonin and hypnotics, or a combination of both.
How can we prevent circadian rhythm disorders?
Preventing circadian rhythm disorders involves properly aligning biological rhythms and the natural light-dark cycle. This can be achieved through regular exposure to natural light during the day, particularly in the morning, to help synchronize the internal clock. Avoiding bright artificial light, especially blue light, during the evening is equally important to prevent delays in sleep onset. Additionally, following a consistent sleep-wake schedule, even on weekends, can strengthen the circadian rhythms.
Summary
Maintaining a healthy circadian rhythm and a consistent sleep schedule is essential for regulating critical biological processes, promoting overall health, and enhancing well-being. Understanding circadian sleep disorders is essential for minimizing their effects on both physical and mental health. If you experience persistent sleep difficulties—such as trouble falling asleep, staying asleep, waking up in the morning, or feeling excessively tired during the day—it is important to consult a healthcare provider, as disruptions to your circadian rhythm can significantly impact your health.
* Chronotype describes an individual's natural preference for sleep and wake times, which is influenced by the circadian clock.
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