The Circadian Rhythm is your body’s natural biological clock, which is roughly 24 hours long and creates physical and mental changes within us. It has a central role in many processes such as digestion, immune response, heart rate, cell metabolism and sleep.
The term circadian comes from the Latin phrase “circa diem,” which means “around a day.”
The sleep-wake cycle is the most recognised circadian rhythm where we become tired and sleep at night and awake and alert throughout the day. The sleep-wake cycle responds to external clues (zeitbergers), in particular the amount of light available. As darkness sets in, a message is sent from the body’s biological clock to slow down and get ready to sleep.
In humans, the circadian rhythms are connected to an internal master clock, a group of about 20,000 nerve cells that form a structure called suprachiasmatic nucleus or SCN, located within the hypothalamus. The SCN is highly sensitive to light cues which are received by direct input from the eyes.

A Disturbed Sleep Cycle
If the circadian rhythm of sleep is off it and the internal clock isn’t signalling properly then someone can experience:
- Difficulty falling asleep
- Wake up more often through the night
- Unable to sleep as long as needed in the morning
- Total sleep can be reduced
- Shallow, fragmented and low quality sleep
What Can Disrupt Circadian Rhythm?
Disruptions to circadian rhythm can occur due to individual behaviour such as:
- Jet lag (changing time zones)
- Shift work
- Late night socialising
Note: The seasonal change of clocks can affect our internal biological clock.
Circadian disruption disorders:
- Advanced sleep phase disorder: People with this rare type of disruption find that they get tired early in the evening and wake up very early in the morning. Even if they want to be up later at night or sleep later in the morning, people with an advanced sleep phase disorder usually cannot do so.
- Delayed sleep-wake phase syndrome:This type of circadian rhythm disruption is associated with staying up late at night and sleeping in late in the morning. The exact cause is unknown, but delayed sleep-wake phase syndrome may be related to genetics, underlying physical conditions, and a person’s behaviour.
- Non-24-hour sleep wake disorder: Non-24-hour sleep wake disorder occurs primarily in people who are blind and are not able to receive light-based cues for their circadian rhythm. Their body still follows a 24-hour cycle, but their sleeping hours constantly shift backward by minutes or hours at a time.
- Irregular sleep-wake rhythm disorder: People with this rare disorder have no consistent pattern to their sleep and may have many naps or short sleeping periods throughout a 24-hour day. Irregular sleep-wake rhythm disorder is frequently connected to conditions that affect the brain.
Any of the above disorders would need to be checked out by a physician and appropriate help sought.