What Circadian Rhythm Means

The circadian rhythm is the biological system that regulates when the body feels awake and when it feels ready for sleep. This internal timing system operates on a roughly twenty four hour cycle and influences many functions including sleep, hormone release, digestion and body temperature.

The circadian rhythm acts as the body’s internal clock, helping align sleep patterns with the natural cycle of day and night.

How the circadian rhythm is controlled

The circadian rhythm is controlled by a small group of cells in the brain known as the suprachiasmatic nucleus, located within the hypothalamus. This region receives signals from the eyes about light levels in the environment.

When light enters the eyes, signals are sent to the brain indicating that it is daytime. This suppresses the production of melatonin, a hormone that promotes sleep.

As evening approaches and light levels fall, melatonin production increases and the body begins preparing for sleep.

The role of light exposure

Light is the most powerful regulator of circadian rhythms. Exposure to natural daylight during the morning helps maintain a stable internal clock, while darkness in the evening encourages melatonin production.

Artificial light, particularly from screens and electronic devices, can interfere with this process by signalling to the brain that it is still daytime.

What happens when circadian rhythms are disrupted

When circadian rhythms become misaligned with the external environment, sleep problems can occur. Irregular work schedules, frequent travel across time zones and inconsistent sleep times can all disrupt the internal clock.

This disruption can make it difficult to fall asleep, stay asleep or wake feeling refreshed.

Supporting a stable circadian rhythm

Maintaining regular sleep and wake times helps reinforce the circadian rhythm. Exposure to daylight during the day and reducing bright light in the evening also support healthy sleep timing.

When the circadian rhythm is stable, the body naturally transitions between alertness during the day and sleepiness at night.

References

Harvard Medical School Division of Sleep Medicine

National Institutes of Health Circadian Rhythm Research

Czeisler CA. Circadian Rhythms and Human Performance