Circadian Rhythm, Sleep and Health

Humans, animals, and all manner of living organisms all operate according to a schedule that balances sleep cycles and metabolism. These cycles, known as circadian rhythms, are physical, mental, and behavioral changes in the body that influence the release of hormones and manage various bodily functions.

Typically, a circadian rhythm is a 24-hour cycle in the physiological processes of living beings, including plants and microorganisms. Normally, circadian rhythms are endogenously generated, although these patterns can be altered by way of external cues, like sunlight and temperature.

The survival of any organism depends on its ability to adapt to changes in the environment and its anticipation of the day ahead. Circadian rhythms are often referred to as the internal body clock because they regulate the sleep and wake cycles. Release of the hormone melatonin rises at night and decreases during day, thereby influencing when one falls asleep. Flowers ready themselves for pollination by opening their petals at correct times, and nocturnal animals awaken at sunset.

When the circadian rhythm fluctuates or when someone is unable to follow a set schedule for sleeping and waking, it may be due to a circadian rhythm disorder, or sleep disorder. Insomnia, jet lag, and shift work disorder, to name a few are all due to imbalances or irregularities in the circadian rhythm and can have various effects on one’s health and overall lifestyle. This paper looks at the different kinds of disorders and the role the circadian rhythm plays in the lives of human beings.

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Circadian Rhythms: Effects and Disorders

A circadian rhythm (often called the internal clock) is a natural, internal process that regulates the sleep-wake cycle and repeats itself approximately every 24 hours. However, this term can also refer to any biological process that displays an endogenous, flexible oscillation of approximately 24 hours.

The circadian rhythm is primarily controlled by a part of the hypothalamus. Despite this, some outside factors such as light, darkness, and temperature can have an impact on the cycle. Circadian rhythms also influence the release of hormones, eating habits, digestion, body temperature, as well as many other important bodily functions.

Still, there are times when the biological clock runs too fast or too slow, which then results in a disrupted or abnormal circadian rhythm. Even though it may sometimes be necessary to adjust one’s sleep-wake cycle due to travel or work shifts, people should generally sleep at set times consistently because a steady sleep-wake cycle will make them feel rejuvenated after a night of rest.

Yet, despite their efforts, some people are unable to get a satisfactory level of rest. Even if they do get an adequate amount of sleep, due to disruptions or disorders within the circadian rhythm, this can become a very trying feat.

The Role of Circadian Rhythms

Circadian rhythms are the physical, mental, and behavioral changes in the body that influence hormone release and other bodily functions. Circadian rhythms are not only important to the sleep-wake cycle, but metabolism as well. In this sense, the time of day in which someone eats effects how their body processes food. Therefore, it is often recommended to not eat late at night.

Regardless, circadian rhythms allow people to maintain a stable relationship with their environment, thus adjusting the physiological variables which are needed for one’s survival (Pontes et al., 2010). This relationship allows one to become synchronized to their environment.

An important role of the circadian rhythm is the regulation of the sleep-wake cycle. Sleep is a necessity for normal psychological functioning, likewise, psychological function affects sleep integrity in turn (Cronin-Golomb, 2016). Circadian rhythms are often correlated to the biological clock. While they are not the same thing, they are indeed related. Biological clocks are able to produce their own rhythms and control their scheduling.

The suprachiasmatic nucleus (SCN) is a section in the brain that is found in the hypothalamus and is basically the body’s “master clock” because it synchronizes all the biological clocks in the individual. The body produces circadian rhythms through natural factors inside the body.

Nevertheless, outside signals from the environment can have an impact, and play a role in resetting the biological clock. Light, being the main influencing cue for circadian rhythms; the SCN receives direct light feedback from the eyes and modifies the biological clocks rhythm appropriately.

The light feedback that is sent to the SCN can turn on or off the genes that manage the framework of biological clocks. Shits that occur from the levels of light can accelerate, delay, or reset biological clocks and circadian rhythms as well.

Circadian rhythms play a critical role in proper body function and overall health. They influence sleeping and waking periods, the release of hormones, eating habits and digestion, body temperature, and other vital bodily functions.

If a biological clock runs too fast or too slow, it can result in a disrupted, or sometimes, abnormal circadian rhythm. Irregular rhythms have can cause a variety of chronic health conditions, such as sleeping ailments, obesity, diabetes, depression, bipolar disorder, and various other conditions that arise from improper bodily timing.

Circadian rhythms help determine one’s sleep patterns. The SCN, controls the production of melatonin, the hormone that makes the body ready sleep by inducing drowsiness. Since the SCN relies on light from the optic nerves, which relay the feedback from the eyes to the brain, when there is not as much light, like at nighttime, the SCN tells the brain to make more melatonin to make one feel drowsy and sleep. Physical exercise can also help with regulating the circadian rhythm by promoting health and overall well being (Maia, Sousa, & Azevedo, 2011).

Irregular rhythms are often present in young children who do not follow a specific sleep-wake schedule. Without a proper understanding of sleep disorders and other variables, professionals may misattribute developmentally appropriate behavior as problem behavior (Schreck, 2010). Therefore, it is necessary to have an understanding of the normal parameters for childhood sleep in order to determine if abnormal sleep-wake patterns do exist.

Moreover, in the modern age there has been an increase in shift work and exposure to (blue) light from mobile devices during the night. There has been prevalent ongoing research regarding how the use of mobile devices during the night may alter circadian rhythms and sleep-wake cycles (Lowden et al, 2010). Since the SCN alters the biological clocks through light input, consequently, light from TVs, computer screens, and mobile devices during nighttime may as well adjust the sleep-wake cycle for many individuals.

Circadian Rhythm Disorders

Circadian rhythm disorders are disruptions in a person’s circadian rhythm. These disorders include conditions in which the sleep times are out of alignment. Someone with one of these disorders does not follow normal sleep times at night and may experience negative effects.

Delayed Sleep-Wake Phase

Delayed sleep-wake phase disorder (DSPD) is a circadian rhythm disorder which consists of a typical sleep pattern that is delayed by two or more hours. “DSPD can range from mild to severe and affects not only an individual’s sleep but also daytime functioning” (Lack, Wright, & Bootzin, 2009, para. 37).

This delay occurs when one’s circadian rhythm is shifted later at night and later in the morning. Once it occurs, sleep is generally normal. However, the delay leads to a pattern of sleep that is later than what is desired or what is considered socially acceptable. This pattern of sleep can be especially troublesome when it interferes with work, school, or social demands.

Advanced Sleep-Wake Phase

Advanced sleep-wake disorder (ASPD) is a circadian rhythm disorder which occurs in people who sleep at times that seem to be out of the ordinary. People who have ASPD are typically early risers. They fall asleep several hours before a normal bedtime, and as a result, they also wake up hours earlier than most people do. Some people with ASPD are able to cope with this early schedule.

While ASPD may be inconvenient for most people and, “·as the condition is classically related to an aberration in the timing (but not quality) of sleep, the characterization of a disorder is invoked only if the schedule interferes significantly with social or occupational functioning” (Auger, 2009, para. 5). Even when they are deprived of sleep, people with ASPD will still wake up early.

Irregular Sleep-Wake Rhythm

People who have irregular sleep-wake rhythm disorder (ISWRD) have sleep times that appear to be out of alignment. This is another kind of sleep pattern that does not follow a normal schedule. People with this condition have sleep-wake cycles that are so disorganized that there is no clear pattern at all. Those who have this sleep-wake disorder may sleep on and off in a series of naps over a 24-hour period.

Their sleep pattern is broken into so many pieces that it is similar to infants who tend to sleep for a few hours and then stay awake for a few hours at a time. “Although sleeping and waking periods are fragmented, the longest sleep period usually is between 2 and 6 am” (Zee & Vitiello, 2009, para. 5).

During the day, they seem to be sleepy because of their frequent amount of naps. During the night, they seem to have insomnia due to them being awake for long periods throughout the night. Because their sleep pattern is broken into pieces all day and night, there is no set sleep time that happens at any time of the day.

Non-24-Hour Sleep-Wake Rhythm

Another sleep-wake rhythm with an irregular pattern is the non-24-hour sleep-wake rhythm. People with this disorder do not follow normal sleep times at night. In fact, those with this sleep-wake cycle shift their sleep patterns a little later each day. Sleeping and waking times continue to move later and later each day. Therefore, someone’s sleep times would go in and out of alignment with other people as weeks go by.

Normally, people have a circadian rhythm that is a little bit longer than 24 hours. Each day, sunlight and other behaviors help reset the sleep-wake cycle according to a 24-hour schedule. Without light and the clock resetting it brings, one’s sleep time would drift later and later into the day.

This is why many people who have non-24-hour sleep-wake rhythms are blind. Since light has a major influence on resetting the sleep-wake cycle, those who are blind tend to have difficulty following a set 24-hour schedule (Uchiyama & Lockley, 2009).

Shift Work

Shift work is the term used to describe work schedules that occur when most people are asleep. Shift work disorder occurs when one has difficulty adjusting to this work schedule. When someone has shift work disorder, there is a conflict between their body’s circadian rhythm and their work schedule.

The common routine for people with shift work disorder is that when they have to be at work their body wants them to sleep, and then when they try to sleep their body expects them to stay awake. Shift workers usually only get about four to six hours of sleep, and are often unable to return to sleep, presumably due to the internal clock promoting wakefulness during the schedule-induced circadian misalignment (Akerstedt & Wright, 2009).

Perhaps the most significant side affect of shift work is the impact on work performance and safety due to sleepiness. The link between safety and night work is most pronounced in road transport, where single-vehicle truck accidents are the most probable at night (Akerstedt & Wright, 2009).

Jet Lag

Jet lag, one of the most reoccurring instances of internal clock disturbance, occurs when travel disrupts the circadian rhythm. When someone passes through different time zones, their biological clock will be different from the local time. For example, if someone flies from the east coast to the west coast, they have gained 3 hours.

If they happen to awaken at 03:00 on the west coast, their biological clock is still running on east cost time, so they would feel the way they might feel at 06:00. It usually takes 24 hours for the biological clock to accommodate for each hour of difference. Since the example was a 3-hour difference, it would take about 3 days for one’s biological clock to reset to the local time.

Consequently, frequent jet travel can have long term health risks. Cognitive deficits, temporal lobe atrophy, disturbances in the menstrual cycle, as well as an increased risk of cancer for those who frequently fly across many time zones, can all occur with frequent jet travel (Eastman & Burgess, 2009).


Insomnia is the most common sleep complaint, affecting about one in three people. It may include difficulty falling asleep, difficulty staying asleep throughout the night, or waking up too early in the morning and being unable to go back to sleep. While insomnia is not directly caused by irregularities in the circadian rhythm, it does negatively affect the sleep-wake cycle by causing sleep disturbances and daytime symptoms.

The severity of insomnia may vary from person to person, but most people with insomnia report a worse overall quality of life. Although many people have the occasional night of poor sleep, that does not mean they have insomnia. It only means that they did not get enough sleep, probably due to staying up too late or waking up too early.

There are two types of insomnia: short-term insomnia and chronic insomnia. Short-term insomnia is usually brief and can last for up to three months. Chronic insomnia occurs at least three times per week and lasts for at least three months. Insomnia is more common in older adults, women, people under stress, and people with certain medical and mental health problems like depression.

Treatment and Therapy

A good night’s sleep is essential for one’s optimal health, performance, and safety on the job. Many of the disorders mentioned above can be treated or prevented by either taking precautions in advance or by taking appropriate after measures.


Melatonin is a hormone that is widely available in a supplemental form. This hormone is naturally produced by the body and plays a critical role in sleep. It helps regulate the body’s sleep-wake cycle by indicating when the time for sleep is approaching. Melatonin supplements are useful and effective for treating circadian rhythm disorders such as jet lag, shift work, DSPD, and even insomnia.

As night begins to fall and it becomes darker, the pineal gland in the brain produces melatonin. The hormone sends signals to the part of the brain that regulates the circadian rhythm and the body prepares itself for sleep. Melatonin levels normally rise in the evening and remain high throughout the night.

Melatonin levels being to drop in the morning before the body begins to wake up. Light helps determine the amount of melatonin that the body produces. The timing of melatonin production during the wintertime can change based on exposure to light.

Age also has a significant impact on melatonin production as many older adults may secrete little to no melatonin at all. Additionally, as one gets older their sleep patterns begin to change. Therefore, individual differences in sleep must be considered in order to maintain a good quality of sleep (Lewandowski, Rosipal, & Dorffner, 2013).

Cognitive Behavioral Therapy

Cognitive behavioral therapy (CBT) helps one to change the actions or thoughts that hurt their ability to sleep well. This kind of therapy helps one to develop habits that promote a healthy sleep pattern. The most common forms of CBT are: stimulus control, sleep restriction, relaxation training and biofeedback, cognitive control and psychotherapy, and sleep hygiene training. These are all good methods one can use to get their circadian rhythms back on track.

Bright Light Therapy

Light therapy is an effective treatment for those who suffer from circadian rhythm sleep disorders since light helps reset the circadian rhythm. “Although the effects of light on the circadian rhythm are not clearly understood, “It is likely that the intensity, spectral distribution, and temporal pattern of light can all affect the relative contribution of different photoreceptors to circadian responses” (Duffy & Czeisler, 2009, para. 3).

Sleep Medications

Sleep medication can be used to reduce some sleep-related issues. There are many different medications that target specific parts of the brain. Since the brain is the part of the body that controls when one’s body sleeps and wakes up, medication can provide much needed relief for someone with a severe sleep disorder.

Taking sleep medication may help promote good health and an overall sense of well being. However, there is a potential risk with the use of any medication and many people may experience some side effects. Therefore, one should not take any medication without the approval of their medical provider.


The circadian rhythms are the physical, mental, and behavioral changes that follow a daily cycle. They respond primarily to the fluctuations of light and darkness in the environment. Sleeping at night and being awake throughout the day is an example of a normal, light-influenced circadian rhythm.

Still, there are occasions when the circadian rhythm goes out of balance. This can lead to a number of disorders that interrupt the body’s everyday functioning by disrupting the sleep-wake cycle. There are many countermeasures for these disorders, but the overall outcome depends of the individual’s lifestyle.

Indeed, while it may sometimes be necessary to adjust one’s sleep-wake cycle due to travel or work shifts, people should do their best to sleep at set times consistently in order to maintain a healthy circadian rhythm.

Understanding what makes biological clocks tick can make way for better treatments for disorders regarding sleep, metabolism, mental health, circadian rhythms, and various other health problems. Knowing in what manner the circadian rhythm works can also develop better ways for individuals to adjust to shift work. Finally, learning about the inner workings of the circadian rhythm will fundamentally assist in the understanding of the biological systems and the human body.

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Circadian Rhythm, Sleep and Health. (2019, Dec 08). Retrieved from

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