Sleep, Circadian Rhythm and its Disorders

Sleep is an integral part of our lives and a crucial fundamental need of our body besides food and water. We spend around 30% of our lifetime in sleep. Disturbance or interruption in sleep may lead to affected brain activity, decreased concentration, and sometimes disorder in our behavior. One of the well known facts is that our sleep and wake state is regulated by a hidden biological clock.

Sleep Chronobiology

Chronobiology is a multidisciplinary branch of Science that includes study of biological rhythms (Chronos – time; bios – life; logos – science). Biological Rhythms are pervasive in all living organisms right from simple unicellular microbes (Cyanobacteria) to complex multicellular organisms like us. When these biological rhythms are dictated by the solar and lunar rhythms, they are called as Circadian Rhythms (circa – approximately; dies – day or 24 hours). Circadian rhythms are physical, mental and behavioral changes that we follow on a daily cycle. Sleeping at night and being awake during the day is an example of a light-related circadian rhythm.

On the other hand, the biological clock is a natural timing device that regulates the cycle of Circadian Rhythms. The biological clock consists of a set of genes that synthesises proteins called as biological clock proteins. Switching ON and OFF of these genes causes increase and decrease of biological clock proteins respectively. These proteins are involved in carrying out various biochemical, hormonal, and metabolic activity of the body. In some organisms, the RNA also plays a role in regulating biological clock genes.

Jeffrey C. Hall, Michael Rosbash, and Michael W. Young had won the Nobel Prize in 2017 for their research in Circadian Rhythms. They discovered the role of genes in regulating the biological clock. They studied this phenomenon in fruit flies and found the rise and decrease of particular protein in day and night time that affects sleep and activeness.

The Master Clock supervises the biological clock; it ticks in our brain region called as suprachiasmatic nuclei (SCN). It receives signals of light and darkness through our eyes. These signals lead to a cascade of reactions and determine physiology and behavior. When a light is received, the hypothalamus sends a signal in the form neurotransmitter to cerebral cortex and keeps the brain active. Brain cells of Hypothamalus releases orexin/Hypocretin, which further induces the release of neurotransmitters, like Histamine, Serotonin, norepinephrine, acetylcholine, and dopamine. They all work together to keep us stay awake. When we remain awake for longer periods of time, there is an accumulation of adenosine that may make us feel sleepy. Caffeine has anti-adenosine effects, which inhibits its action and helps us stay awake.

When we are not exposed to light, various neurotransmitters and hormones keep us asleep. Neurotransmitters like GABA, Adenosine, Nitric oxide and melatonin hormone are responsible for inducing sleep.

Study has found that blind people have unsynchronized circadian cycle because light cannot enter through their eyes due to which there is no cascade of reaction.

You might have witnessed the disturbance of your Circadian Rhythm when you had slept during an odd time. When you get up from such an odd sleeping time, you feel drowsier rather than feeling fresh. This is because this sleep was not scheduled by your internal biological clock and hence you might need some time to feel normal.

The hidden clock regulates our sleep cycle, hormonal level, appetite, body temperature, blood pressure, and overall health. Hence, when the cycle gets disturbed, it may lead to several disorders.

Factors that affect Circadian Rhythm-

  1. Job shifts (Night shift/ Early morning shift/ Evening shift or rotating shifts).
  2. Travelling frequently across time zones.
  3. Life style and stress.
  4. Gene mutation (involved in regulating circadian rhythm.
  5. Watching electronic device’s screen at night.

Circadian Rhythm Disorders

Delayed Sleep Phase Syndrome (DSPS)

Delayed Sleep Phase Syndrome (DSPS) is a disorder in which a person’s sleep is delayed by few hours than the acceptable or conventional bedtime. The delayed sleep then causes difficulty in being able to wake up at the desired time. The people who stays awake until 1 a.m. or more comes under Delayed Sleep Phase Syndrome. Teenagers and young adults are more prone to stay awake in late nights. Social media, night out, and late night parties on a regular basis can make a person a victim of Delayed Sleep Phase Syndrome.

Advanced Sleep Phase Syndrome (ASPS)

Advanced Phase Sleep Syndrome (ASPD) is a disruption of the Circadian Rhythm, where a person sleeps and wakes up early than the normal time. Such people are called as “Morning People”. Such sleep pattern is mostly seen in adults and senior citizens.

Time zone change syndrome or Jet lag

Time zone change syndrome, also known as Jet lag or desynchronosis, occurs when people travel rapidly across time zones. After moving to a new time zone, the body tends to follow the former time zone and needs time to adapt to new timings. This could be a temporary phase, if a person travels less frequently across the time zone. But the syndrome may get severe if the person travels and changes the time zone frequently.

Shift Worker Disorder-

This disorder is caused due to a professional or job life style where a person needs to switch duties as per the need. The factory and Industry workers, Hospital, Hospitality, Police employees may have different shifts like night shifts, early morning shifts, evening shifts or rotating shifts. People working in such shifts may feel sleep deprived and it could lead to several diseases and disorders.

Some people may not have any of the above-mentioned disorders but may have an irregular circadian rhythm, which leads to fragmented sleep. Such people urge to get sound sleep. They are also know as “Light Sleepers”.

Why is it important to maintain or circadian rhythm?

The circadian cycle operates and maintains all the physiological, biochemical, and molecular reactions from time to time. These reactions have a direct impact on our physical and mental state. People with disturbed circadian cycles are prone to get diabetes, blood pressure, cholesterol, heart disease, obesity, stress, anxiety, and depression.

How to overcome?

Always listen to your internal clock and follow its prescribed schedule. One needs to take healthy diet and exercise regularly.


(2008). Circadian Rhythm Sleep Disorder. Darien: American Academy of Sleep Medicine.

Kumar Pati, A. (2001). Chronobiology: The Dimension of Time in Biology and Medicine. Proc. Indian natn Sci Acad., 323-324.

Pati, A. (2001). Cheonobiology: The Dimension of Time in Biology and Medicine. Proc. Indian natn Sci Acad.(PINSA), 323-324.

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