Why do we wake up when there is light, and why do we sleep when there is darkness? Why do we feel the need to recharge ourselves through sleep, like a drained battery?
The human body has developed its own biological clock in response to environmental factors such as light and temperature.
Circadian Rhythm Sleep Disorder
This clock is often called the circadian clock or circadian rhythm/cycle. It's a 24-hour cycle that affects numerous physiological processes other than our sleep-wake cycle.
It is evident in hormonal levels fluctuations, heart rate, body temperature, cell cycle, feeding, etc. What happens to your body in response to an irregular circadian cycle? Here, we'll explore circadian rhythm abnormalities and what you can do to improve the cycle.
What Is A Circadian Clock?
The circadian cycle is generated, in mammals, by a circadian pacemaker located in the suprachiasmatic nuclei (SCN) of the brain's hypothalamus .
The reason this master clock is essential is that it anticipates environmental changes instead of reacting to them. This is a result of evolution.
The circadian system in the body consists of the circadian pacemaker and peripheral oscillators located in tissues such as lungs, muscles, heart, liver, retina, etc. . This cycle is activated by external cues as well as internal cues:
- Light: the most important cue. Receptors receive light in the retina, then transmitted to the SCN, activating genes responsible for the circadian rhythm .
- Feeding: the timing of your food intake is a critical cue .
- Temperature: the external temperature influences your body's circadian rhythm. Freezing and scorching temperatures affect your sleeping cycle by making you more alert or sleepier .
- Internal factors such as the metabolic state .
Due to its implications in many physiological, behavioral, and physiological aspects, disruption in the circadian rhythm could lead to many disorders.
Circadian Clock: The Disorders
Symptoms & Diagnosis
Individuals experiencing circadian sleep-wake disorders may experience all or some of the following symptoms [7,8]:
- Difficulty falling asleep (insomnia)
- Difficulty waking up
- Excessive sleepiness
- Daytime sleepiness
The diagnosis is made after documenting a sleep log for at least seven days and after clinical assessment. Based on the sleeping log, clinical and family history evaluations, the following disorders could be diagnosed.
Circadian Rhythm Sleep Disorders
Abnormalities in the circadian cycle deeply affect the quality and quantity of sleep. Circadian rhythm sleep disorders (CRSD) are characterized by sleep disruption caused by changes in the circadian cycle. There are many types of CRSDs.
1) Delayed Sleep-Wake Phase Disorder
People with delayed sleep-wake phase disorder have a natural sleep-wake cycle that is delayed with respect to a conventional one. They often experience insomnia and sleep later at night, sometimes even in the early hours of the morning, and have trouble waking up in the morning .
2) Advanced Sleep-Wake Phase Disorder
This disorder is the opposite of the delayed sleep-wake phase one; individuals fall asleep and wake up earlier than usual . Individuals experiencing advanced sleep-wake disorder often sleep before 8-9 pm and wake up between 2-5 am. It is less common than delayed sleep-wake phase disorder and has less impact on the individual's quality of life.
3) Irregular Sleep-Wake Rhythm Disorder
It is characterized by a disrupted sleep-wake cycle in which the individuals sleep and wake up repeatedly throughout one circadian cycle (24 hours). This does not mean that they are not getting enough sleep, but instead of sleeping for several hours at once, their sleeping hours are spread out throughout the day. This disorder is primarily seen in older individuals with either dementia or developmental disorder such as Alzheimer's .
4) Non-24-Hour Sleep-Wake Disorder
In this disorder, the 24-hour cycle is disrupted. People experiencing the disorder would sleep and wake up without any specific pattern and in no particular hours, alternating between sleeping during the daytime and the nighttime. They often experience insomnia and daytime sleepiness. This disorder is most seen in blind people .
5) Metabolic Disorders
The circadian cycle affects metabolic processes such as glucose metabolism, lipid metabolism as well as cholesterol metabolism. The genes of the circadian clock have been linked to metabolic disorders.
In a study done on mice where the circadian clock genes were artificially mutated, the mice had multiple disorders such as obesity, hyperglycemia, hyperinsulinemia, as well as disorders of the liver and lipids .
In humans, glucose tolerance was shown to be affected by the circadian cycle; the glycemic control was decreased at night in healthy adults . Additionally, recent studies showed that sleep delay caused impairment in insulin and lipid levels .
How Can You Improve Your Circadian Cycle?
If you are diagnosed with a circadian rhythm sleep disorder, the treatment will vary depending on the type:
- Delayed sleep-wake phase disorder: the patients are given low doses of melatonin (a naturally produced hormone that induces sleep) and exposure to bright light for at least 30 minutes as soon as they wake up. The “bright light” can be artificial if it is at least 5000 lux.
- Advanced sleep-wake phase disorder: the treatment is simply exposure to bright for two hours in the evening after 7 pm.
- Irregular sleep-wake rhythm disorder: changes in lifestyle, which include increased daytime light exposure.
- Non-24-hour sleep-wake disorder: for blind people, melatonin is prescribed at night, whereas, for sighted people, bright light is recommended alongside melatonin.
Lifestyle Changes: Taking Matters Into Your Own Hands
You can improve your circadian cycle through lifestyle and behavioral changes.
- Decrease caffeine intake: caffeine is a stimulant that helps you stay awake and alert. Try to decrease your caffeine intake throughout the day and avoid it in the evening.
- Decrease screen-time at night: light, even if artificial, interferes with the circadian cycle.
- Getting enough bright light: preferably natural light, it is best to be exposed to bright light early in the morning.
- Decrease daytime naps: especially long naps, since they can interfere with your sleeping schedule by keeping you up at night.
- Have a consistent sleeping schedule: while it is hard to be consistent, especially if your job has daytime and nighttime shifts, it is best to create a routine for your body.
- Avoid having all-nighters: don't binge-watch that Netflix show; get yourself in bed and sleep.
- Light exercises: avoid high-intensity workouts in the evening and opt for low-intensity ones such as walking.
Circadian Rhythm Sleep Disorder: Summing Up
The circadian cycle is an endogenous evolutionary clock that has helped us adapt to daily changes in the environment, such as light/darkness.
It affects our sleep-wake cycle as well as numerous metabolic and physiological behaviors. The most important stimulus for the circadian cycle is light.
It is perceived by our retina and transmitted to cells in our brain that control the circadian cycle.
Disruptions in the circadian sleep-wake cycle lead to different types of sleeping disorders and metabolic disorders. The disruptions are often caused by lifestyle choices such as:
- Disrupted or irregular sleeping schedule.
- Constantly staying up later than usual
- Excessive caffeine intake
- Lack of bright light exposure.
The circadian clock is essential for your body's function, for health and longevity. Maintain a healthy circadian cycle by having a consistent sleeping schedule and a good exposure to bright light. If our tips were unable to help you, don't hesitate to contact your healthcare provider.