What else does circadian rhythm affect besides sleep?

Before life was born, the earth was already rotating 24 hours a day. The sun rises on the top of a mountain and sets on the west; the change of light and shadow is the initial condition of the world.

3.5 billion years ago, when the first single cell was born on Earth, it began to be affected by natural selection. Over billions of years, the Earth's environment has undergone tremendous changes, but the only thing that remains unchanged is the alternation of day and night.

During the long process of evolution, organisms have evolved a set of physiological mechanisms that are synchronized with day and night, namely the circadian rhythm.

01 What is circadian rhythm?

Circadian rhythm is a biological rhythm that is universally present in all living things on Earth. It is closely related to the alternation of light and dark during the Earth's rotation.

The suprachiasmatic nucleus (SCN) of the thalamus is the pacemaker of the body's circadian rhythm. It precisely controls the biological clocks of eating/fasting and wakefulness/sleep in animals, while plant photosynthesis is also regulated by the circadian rhythm.

The 2017 Nobel Prize in Physiology or Medicine was awarded to three scientists who revealed the molecular regulatory mechanism of circadian rhythms. In their experiments, they discovered that there is a period gene expressing Per protein and a timeless gene expressing TIM protein in the thalamus of fruit flies. At night, Per protein will bind to TIM protein and enter the nucleus from the cytoplasm and be stored and accumulated in the nucleus. During the day, Per protein accumulated in the nucleus will gradually degrade. The process of Per protein accumulation and degradation corresponds exactly to the night and day of the earth, and this cycle is very close to 24 hours.

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02 Circadian Rhythm and Sleep

When people talk about circadian rhythms, it’s usually in the context of sleep. The sleep-wake cycle is one of the clearest and most critical examples of the importance of circadian rhythms.

During the day, light exposure signals the master clock to keep us alert, helping us stay awake and active. As night falls, the master clock begins to produce melatonin, a sleep-promoting hormone, which then continues to send signals to help us stay asleep throughout the night.

In this way, our circadian rhythm aligns our sleep and wakefulness with day and night, creating a steady cycle of restorative rest that increases daytime activity.

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03 Circadian Rhythm and Health

While the sleep-wake cycle is one of the most prominent circadian rhythms, these 24-hour internal clocks play a vital role in nearly all systems in the body.

Research continues to uncover details about circadian rhythms, but evidence suggests they are linked to metabolism and weight through the regulation of blood sugar and cholesterol. Circadian rhythms also influence mental health, including the risk of developing psychiatric illnesses such as depression and bipolar disorder, and the likelihood of developing neurodegenerative diseases such as dementia.

There are signs that circadian rhythms have important effects on the immune system and on DNA repair processes involved in preventing cancer. Early studies have shown that circadian rhythms can affect the effectiveness of anti-cancer drugs, and new drugs may be able to use the body clock to kill cancer cells.

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04 What happens if circadian rhythm is disrupted?

When the circadian rhythm is disrupted, it means the body's systems don't function optimally.

A disrupted sleep-wake circadian rhythm can lead to serious sleep problems. Without the right signals from the body's internal clock, a person may have trouble falling asleep, wake during the night, or be unable to sleep as long as they would like in the morning. Their total sleep time may decrease, and a disrupted circadian rhythm may also mean that sleep is shallow, fragmented, and of reduced quality.

Additionally, research has identified circadian rhythm disruption as a potential cause of obstructive sleep apnea (OSA), a sleep disorder characterized by repeated interruptions in breathing. OSA reduces the body’s oxygen levels and causes disrupted sleep throughout the night.

Overall, a disrupted circadian rhythm can negatively impact sleep in many ways, increasing a person’s risk for insomnia and excessive daytime sleepiness. Given the importance of sleep to productivity and overall health, when a person’s circadian rhythm is out of whack, there are often significant consequences.

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05 How to maintain a good circadian rhythm

While we can’t completely control our circadian rhythms, there are some healthy sleep techniques we can adopt to try to better guide our 24-hour sleep cycles.

Exposure to natural light, especially early in the day, helps reinforce the strongest circadian signals.

Maintain a regular sleep and sleep schedule.

Activity during the day can support your internal clock and help you fall asleep more easily at night.

Avoid coffee after noon; stimulants like caffeine can keep you awake and disrupt the natural balance between sleep and wakefulness.

Experts recommend dimming the lights and putting down electronic devices before bed, and keeping electronic devices away from the bedroom and mattress.

These steps to improve sleep hygiene can be an important part of supporting a healthy circadian rhythm, but additional steps may be necessary depending on the situation. If you have persistent or severe sleep problems, daytime sleepiness, and/or a problematic sleep schedule, be sure to consult with your healthcare provider.

Reference articles for this article:

Circadian Rhythm

By Eric Suni