晝夜節律是 24 小時循環，是身體內部時鐘的一部分，在後台運行以執行基本功能和過程。最重要和最著名的晝夜節律之一是睡眠-覺醒週期。

身體的不同系統遵循與大腦中的主時鐘同步的晝夜節律。這個主時鐘直接受到環境線索的影響，尤其是光線，這就是為什麼晝夜節律與晝夜循環聯繫在一起的原因。

如果正確對齊，晝夜節律可以促進一致和恢復性的睡眠。但是，當這種晝夜節律被打破時，就會產生嚴重的睡眠問題，包括失眠。研究還表明，晝夜節律在身心健康的各個方面都發揮著不可或缺的作用。

晝夜節律如何工作？

晝夜節律有助於確保身體的過程在 24 小時內的各個時間點得到優化¹. 晝夜節律一詞來自拉丁短語“circa diem”，²這意味著“大約一天”。

晝夜節律存在於所有類型的生物體中。例如，它們幫助花朵在正確的時間打開和關閉，並防止夜行動物離開它們的庇護所³在白天，它們會接觸到更多的捕食者。

在人類中，晝夜節律協調心理和生理系統⁴遍及全身。消化系統產生蛋白質⁵與典型的進餐時間相匹配，內分泌系統調節激素以適應正常的能量消耗。

The circadian rhythms throughout the body are connected to a master clock,⁶sometimes referred to as the circadian pacemaker, located in the brain. Specifically, it is found in the suprachiasmatic nucleus (SCN), which is in a part of the brain called the hypothalamus. At different times of the day, clock genes⁷ in the SCN send signals to regulate activity throughout the body.

The SCN is highly sensitive to light, which serves as a critical external cue that influences the signals sent by the SCN to coordinate internal clocks in the body. For this reason, circadian rhythms are closely connected to day and night. While other cues, like exercise, social activity, and temperature, can affect the master clock, light is the most powerful influence on circadian rhythms.

Is a Circadian Rhythm the Same As a Biological Clock?

Biological clocks help regulate the timing of bodily processes, including circadian rhythms. A circadian rhythm is an effect of a biological clock, but not all biological clocks are circadian. For instance, plants adjust to changing seasons using a biological clock with timing that is distinct from a 24-hour cycle.

How Does Circadian Rhythm Affect Sleep?

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

During the day, light exposure causes the master clock to send signals that generate alertness⁸ and help keep us awake and active. As night falls, the master clock initiates the production of melatonin, a hormone that promotes sleep, and then keeps transmitting signals that help us stay asleep through the night.

In this way, our circadian rhythm aligns our sleep and wakefulness with day and night⁹ to create a stable cycle of restorative rest that enables increased daytime activity.

What Does Circadian Rhythm Affect Besides Sleep?

While the sleep-wake cycle is one of the most prominent circadian rhythms, these 24-hour internal clocks play a vital role in virtually all systems of the body¹⁰.

Research continues to uncover details about circadian rhythms, but evidence has connected them¹¹ to metabolism and weight through the regulation of blood sugar and cholesterol. Circadian rhythms influence mental health as well, including the risk of psychiatric illnesses like depression and bipolar disorder as well as the potential for neurodegenerative diseases¹² like dementia.

There are indications that circadian rhythms have an important influence on the immune system as well as processes of DNA repair that are involved in preventing cancer¹³. Early-stage research indicates that circadian cycles can influence the effectiveness of anti-cancer drugs¹⁴ and that new medications may be able to harness biological clocks to kill cancer cells.

What Happens When Circadian Rhythm Is Off?

When circadian rhythm is thrown off, it means that the body’s systems don’t function optimally.

A disturbed sleep-wake circadian rhythm can give rise to serious sleeping problems. Without the proper signaling from the body’s internal clock, a person can struggle to fall asleep, wake up during the night, or be unable to sleep as long as they want into the morning. Their total sleep can be reduced, and a disrupted circadian rhythm can also mean shallower, fragmented, and lower-quality sleep.

In addition, studies have identified circadian rhythm disruptions as potential contributors¹⁵ to obstructive sleep apnea (OSA), a sleep disorder marked by repeated lapses in breathing. OSA reduces the body’s oxygen levels and causes numerous sleep interruptions through the night.

As a whole, a misaligned circadian rhythm can negatively affect sleep in many ways, increasing a person’s risk of insomnia and excessive daytime sleepiness. Given the essential role of sleep for productivity and overall health, there are often significant consequences when a person’s circadian rhythm is off.

What Can Disrupt Circadian Rhythm?

Disruptions to circadian rhythm can occur over the short- or long-term. Experts have identified a number of types of circadian rhythm sleep-wake disorders (CRSWD) based on their characteristics and causes.

• Jet Lag Disorder: This occurs when a person crosses multiple time zones in a short period of time and gets its name from the fact that it is often experienced by people who take intercontinental flights. Until a person’s circadian rhythm can acclimate to the day-night cycle of their new location, they are likely to suffer sleeping problems and fatigue from jet lag.
• Shift Work Disorder: Work obligations can cause major disruptions in a person’s circadian rhythm. Shift work, which requires having to work through the night and sleep during the day, puts a person’s sleep schedule directly at odds with the local daylight hours.
• Advanced Sleep Phase Disorder: People with this 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. This disorder is relatively rare, affecting around 1% of people in middle and older age¹⁶, and occurs more frequently in older adults. In some cases, advanced sleep phase disorder may be related to an inherited genetic cause.
• Delayed Sleep Phase Disorder: This type of circadian rhythm disruption is associated with “night owls” who stay up late at night and sleep in late in the morning. It is rare among the general population — affecting just 1 or 2 people out of every 1,000 — but impacts up to 16% of teens. The exact cause is unknown but may be related to genetics, underlying physical conditions, and a person’s behavior.
• Non-24 Hour Sleep Wake Disorder: This condition occurs primarily in people who are blind¹⁷並且無法接收基於光線的晝夜節律提示。他們的身體仍然遵循 24 小時的循環，但他們的睡眠時間會不斷地向後移動幾分鐘或幾小時。
• 不規則的睡眠-覺醒節律障礙：患有這種罕見疾病的人的睡眠模式不一致，並且在 24 小時的一天中可能有很多小睡或短睡眠時間。它經常與影響大腦的條件有關¹⁸，例如癡呆或創傷性腦損傷，會限制下丘腦主時鐘的正常功能。

正如這份清單所示，晝夜節律紊亂有多種原因。一些晝夜節律紊亂與個人行為有關，例如旅行或工作，這會使睡眠時間表與正常的日光暴露不符。其他疾病源於一個潛在的問題，該問題導致無法接收或處理調節身體主時鐘的環境線索。在某些情況下，可能涉及遺傳原因，或者原因可能仍然未知。

如何保持健康的晝夜節律

雖然我們無法完全控制自己的晝夜節律，但可以採取一些健康的睡眠技巧來嘗試更好地引導我們的 24 小時睡眠週期。

• 尋找陽光：暴露在自然光下，尤其是在一天的早些時候，有助於加強最強的晝夜節律信號。
• 遵循一致的睡眠時間表：改變你的就寢時間或早晨起床時間會阻礙你的身體適應穩定的晝夜節律的能力。
• 每天鍛煉：白天的活動可以支持您的內部時鐘，並幫助您在晚上更容易入睡。
• 避免咖啡因：像咖啡因這樣的興奮劑可以讓你保持清醒，並打破睡眠和清醒之間的自然平衡。每個人都不一樣，但如果你有睡眠困難，你應該在中午之後避免攝入咖啡因。
• 睡前限制光照：夜間人工光照會干擾晝夜節律。專家建議在睡前調暗燈光並放下電子設備，並將電子設備遠離臥室和床墊。
• 午睡時間短而早：午睡時間長而晚會推遲你的就寢時間，讓你的睡眠時間變得不平衡。

這些改善睡眠衛生的步驟可能是支持健康的晝夜節律的重要部分，但根據情況可能需要採取其他步驟。如果您有持續或嚴重的睡眠問題、白天嗜睡和/或有問題的睡眠時間表，請務必與最能診斷原因並提供最合適治療的醫生交談。