Understanding the Circadian Rhythm

Author: FITivate | Published date: March 24, 2022 | Category: Medical
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What is the circadian rhythm?

The circadian rhythm consist of a 24 hour cycle where the body functions, reacts and changes differently based on the time of the day (1).  It mainly governs the time period of sleepiness and wakefulness, which is  greatly influenced by bodily and environmental factors such as day light and darkness.

How the circadian rhythm works - what determines it

There are certain factors that define how our circadian rhythm works - the triggers that make us feel drowsy or to stay alert (2). 

Response to light and darkness

The brain responds to daylight and darkness through how we visually capture the amount of light in our environment. Naturally, when night falls, the decrease amount of light gathered will trigger the brain to feel sleepy. Conversely, during day time, the brain is triggered to stay more alert through this period.

Hormone production

Melatonin and Cortisol are hormones that the body produces to aid our bodily functions throughout the day and night. Melatonin is produced in greater amounts at night as it makes the body feel drowsy. On the other hand, Crotisol is produced in the day as it encourages wakefulness and alertness.

Body temperature

Body temperature fluctuates at different parts of the day and with lower activity, typically at night, our body temperature dips when we sleep and rises during our active hours in the day.

External factors  

The circadian rhythm will shift and evolve based on our daily activities, habits and job requirements. However, certain activites can cause our natural circadian rhythm to go out of sync which can have detrimental effects in the long run.


Generally as we age, our melatonin releases tend to vary, with teens usually feeling more sleepy closer to midnight while adults may feel fatigued well before that. Elderlies will tend to go to bed much earlier and wake up in the wee hours of the morning.

Upsetting the natural circadian rhythm

There are certain factors that cause our circadian rhythm to go out of sync and these are usually results of individual choices and habits (3).

Indefinite sleep schedules

It might be hard for many to stick strictly to a fixed sleep and wake timing. For those who tend to get lesser sleep during weekdays and sleep in more during free time, such as weekends or public holidays will ultimately mess up their circadian rhythm.

Jet Lag

As an individual pass through different time zones due to travel, they might find their sleep cycle being thrown into confusion. It takes some time, probably a few days, for the body to adjust back to the current time zone and cycle, but frequent travelling of such arrangements might make take a strain on the body.

Electronic devices 

Many of us might be guilty of this. Using our electronic devices late into the night while lying in bed might keep our brain alert due to the emission of blue light from the screen. Turn off or turn away from all electronic devices and make your bed room as conducive for sleep as possible.

Shift work

Night shift workers will have their natural circadian rhythm almost flipped 180 degrees around, where they might be the most alert at work during the wee hours of the night and sleep through the day. This is not how our body is being programmed and over time, shift work disorder might be experienced, where individuals might find it hard to stay awake at night (during their working hours) and find it difficult to fall asleep during the day (after they knock off).

Delayed and advanced sleep phase disorder

People with advanced sleep disorder are morning people or “lark”. They tend to get sleepy early in the evening and tend to wake up very early in the morning. This disorder affects about 1% of people in the middle and older age group. It can also run in the family line.

Delayed sleep disorders are also known as “night owls” who tend to sleep late at night and wake up late into the morning. It affects about 16% of teens and can be attributed to genetics and even personal habits (4).  

Negative impacts of disrupted circadian rhythm

Here we will discuss 4 common the negative effects of an out of sync circadian rhythm (5).


If individuals are not sleeping at their designated natural circadian rhythm timing, which can be due to shift work or other factors, might experience periods of wakefulness in the wee hours of the night. The quality and duration of restful sleep will ultimately be negatively impacted.

Gaining Weight

Insufficient and lack of quality of sleep can lead to weight gain as it encourages the increased release of a appetite inducing hormone called ghrelin. Insufficient sleep can also cause cravings towards high calorie foods and reduced physical activity due to daytime fatigue.

Reduced productivity

A disrupted circadian rhythm can result in behavioural and cognitive changes which negatively impacts alertness, focus, wakefulness, motor skills and memory. This ultimately results in issues such as workplace errors, drop in work efficiency and even lead to physical injuries.

Mental health

Mood changes can occur from circadian rhythm disruptions. A research showed that as people are exposed to longer incidences of circadian rhythm disruptions, they have a increased risk of mood disorders such as anxiety and depression.

Read more : Top 10 ways to sleep better, naturally

By : Alvin Ho

B (Eng), MBA, Certified Allied Healthcare/Fitness Professional (EIMS), Master Fitness Trainer / Fitness Nutrition, Resistance & Endurance Training Specialist (NFPT)



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