Circadian rhythms of the body: Classification, disorders and treatment

The circadian rhythm is the 24-hour cycle of the “internal body clock” to carry out functions and processes essential for survival. One of the most important and well-known circadian rhythms is the sleep-wake cycle. The following article will talk more about the circadian rhythm of the human body.

The different systems of the body that follow circadian rhythms are synchronized with a "master clock" in our brain. This master clock is directly influenced by environmental cues, especially light, which is why circadian rhythms are tied to the day and night cycles. When properly aligned, circadian rhythms can help with sleep and recovery. However, when this circadian rhythm is disrupted, it can create significant sleep problems, including insomnia. The study also revealed that circadian rhythms play an integral role in aspects of physical and mental health.

The circadian rhythm is the natural cycle of changes in the chemicals or functions in each of us. It is like an internal “master clock” that coordinates the other clocks in your body. With that said, the "master clock" is located in the brain, right above the nerves where the eyes meet. It is made up of thousands of nerve cells that help synchronize the functions and activities of the body.

There are four circadian rhythms:
Circadian rhythms: A 24-hour cycle that includes physiological rhythms and behaviors such as sleep. Day-Night Rhythm: The circadian rhythm synchronizes with day and night. Ultradian rhythm: Circadian rhythms with shorter cycles and higher frequencies than circadian rhythms. Infrared Rhythm: A circadian rhythm that lasts more than 24 hours, such as the menstrual cycle. The circadian clock will play both physical, mental, and behavioral roles in response to light and darkness. This clock helps regulate body functions, including:
Sleep time. Craving time. Body temperature level. Hormone levels. Alertness. Daily performance. Blood pressure . Reaction time to external stimuli. External factors can affect our circadian rhythms. For example, exposure to sunlight, drugs, and caffeine can affect when to fall asleep, when to eat, and many other activities. The body's circadian rhythm controls the sleep or wake cycle. They play a role in sleep due to the way the body and brain respond to darkness, which is when most humans feel tired and tend to want to go to sleep. When darkness covers, the body's biological clock will instruct the cells to slow down. When it gets dark, the hormone melatonin will begin to rise and allow sleep to take place. Melatonin peaks around 2 – 4 a.m. and then, decreases in the morning, allowing us to stay awake and active.

Light is an external factor and is the main factor controlling the body's circadian rhythms. It keeps circadian rhythms in sync with the Earth's natural 24-hour cycle. In addition, other environmental cues that may help synchronize circadian rhythms include food intake and activity levels. However, many things are capable of interrupting this process. While circadian rhythms occur naturally, a number of factors can affect them during the day.

Abnormal light can easily disrupt normal circadian rhythms. According to a report by the US Centers for Disease Control and Prevention (CDC), the circadian clock is most sensitive around 2 hours before a person's usual bedtime. Using bright lights during this time can alter sleep needs and cause the person to sleep later. So a person may be drowsy and sleep later in the evening and wake up later in the morning.
Conversely, bright light in the morning can alter the need to sleep earlier. Sleeping in a bright room can also wake a person up earlier than necessary and alter their normal amount of sleep.

The color of light seems to disrupt biological patterns. Also according to experts from the US Centers for Disease Control and Prevention, light with a blue wavelength has the strongest impact on our circadian rhythms. Blue and white lights during sensitive times of the day, like 2 hours before bedtime, can make it difficult for a person to fall asleep or stay asleep. These light sources are typically emitted by electronic screens on devices such as phones, computers, and televisions. Other wavelengths of light have less effect on the biological clock.

People with unhealthy sleep habits can disrupt the circadian clock during the day. For example:
Going out late and waking up early. No sleep time. Eat and drink late at night. Consume caffeine at night. Use electronic devices at night. Do mentally stimulating activities at the end of your day. Pain or discomfort before and during sleep.

People who work late shifts or work all night are likely to have their natural circadian rhythm disrupted. As the body responds to the sun's natural light and dark cycles, the shift works to alter their circadian rhythms.

Frequent travelers can be disrupted by their sleep and circadian rhythms, especially if they frequently travel between time zones. This is known as jet lag, feeling groggy or tired as the body tries to keep up with the changes of time and new rhythms of the day.

Various types of underlying sleep disorders can also affect circadian rhythms, including:
Late sleep phase syndrome: When a person's circadian rhythms become delayed, they will prefer to go to bed late and stay up wake up later. Advanced sleep phase syndrome: An elevated circadian rhythm causes a person to feel sleepy earlier in the evening and wake up earlier in the morning. Irregular sleep disorders: Irregular rhythms lead to disrupted sleep-wake processes. Sleep-wake disorder without a 24-hour cycle: The circadian rhythm is not synchronized for 24 hours of the day, leading to drowsiness and insomnia.

Disorders can develop when the natural circadian rhythm is disturbed. These disorders include:
Sleep disorders : The body cannot go to sleep at night. Disruption to your body's natural rhythms can lead to affected sleep, including insomnia. Timing Disruption: Disruption of circadian rhythms when traveling across time zones or overnight. Mood disorders: Lack of exposure to sunlight can lead to conditions like depression, bipolar disorder, and seasonal affective disorder (SAD). Shift work disorder: When a person works in shifts, it causes changes in the body's basic circadian rhythm. Circadian rhythm disturbances can affect a person's health and well-being. Some effects of circadian rhythm disturbances may include:
Anxiety, restlessness. Day sleep status. Depression. Lower performance at work. More prone to accidents. Lack of mental alertness. Increased risk of diabetes and obesity. Some of the most important circadian human errors in the world have occurred while working the night shift. Examples include the Chernobyl disaster and the Three Mile Island accident. Also, most car crashes are caused by a pre-dawn driver, according to Cornell University.
From a brain and body perspective, our bodies are born and adapted to sleeping at night. This is why we do not have the ability to see at night or have a more sensitive sense of smell and hearing like nocturnal animals.
It is estimated that about 15% of full-time workers in the United States work in shifts. Shift workers often do service-related jobs that are vital to health and social mobility. They were also more likely to sleep less than six hours per night.
People who work shifts, or work beyond 9am to 5pm every day, are especially at risk for circadian rhythm disturbances. Examples of occupations that involve shift work include:
Healthcare workers. Drivers, pilots and transportation providers. Food preparers, waiters. Police Officer. Fireman. An NSF survey found that 63% of workers feel that their job allows them to get enough sleep. The same survey found that 25 to 30 percent of shift workers had periods of excessive sleepiness or insomnia. Other groups of people at risk for circadian rhythm disturbances include people who frequently travel across time zones or live in places where there is not much daylight, such as Alaska (USA).

Diagnosing a circadian rhythm disorder often requires a careful review of your medical history. The doctor will ask the patient questions such as:
When did you first notice your symptoms? Are there activities that make your symptoms worse? Or are there activities that make your symptoms better (make you happy)? How do symptoms affect you? What drugs are you taking?

Your doctor may also want to rule out other conditions, such as dysglycemia, that can cause similar mood disorder symptoms.
Treatments for circadian rhythm disorders vary and depend on the underlying cause. Example: Airplane delay symptoms will usually be temporary and do not require medical treatment. In the case of shift work or mood disorders, lifestyle changes can be helpful.
Talk to your doctor about more serious symptoms such as fatigue, low mood or depression. Your doctor can prescribe the right treatment and make lifestyle suggestions. For people with seasonal affective disorder (SAD), treatment with “light boxes” can be effective. These light boxes are modeled on daylight and can trigger the release of chemicals that create a feeling of well-being. These chemicals promote alertness in your body.
When lifestyle treatments and good sleep hygiene don't work, your doctor may prescribe medication. Modafinil (Provigil) is for people who have trouble waking up during the day. Your doctor may also prescribe sleeping pills as an option, but sleeping pills should only be used for a short time. Sleeping pills can cause dependence and lead to feelings of excessive sleepiness.
Circadian rhythms are natural cycles that the body goes through every day. The sleep-wake circadian rhythm is the most widely recognized example of circadian rhythms in the human body. Maintaining a healthy circadian rhythm can be about adjusting a person's habits to match nature's rhythms to help prevent some problems falling asleep or waking up. Anyone who is uncertain about their symptoms should talk to their doctor to get a diagnosis and treatment plan in place.
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Reference articles: nigms.nih.gov, medicalnewstoday.com, healthline.com