Circadian rhythms are natural processes that occur throughout the day and exist in all living beings, from plants to animals. They are vital for organisms and continue to take place even in the absence of external factors. In humans, circadian rhythms refer to the 24-hour patterns that the body and brain undergo, leading to changes in the physical and mental states, mood, and behavior.
The sleep-wake cycle is one of the most noticeable circadian rhythms in humans, where people tend to feel tired at night and more alert during the day. However, these rhythms involve more than sleep. Other circadian rhythms in humans include hormonal activity, body temperature, digestion, and immune function.
Is A Circadian Rhythm The Same As A Biological Clock?
Biological clocks play a crucial role in regulating the timing of bodily processes, including circadian rhythms. It’s important to note that not all biological clocks are circadian, and while a circadian rhythm is one effect of a biological clock, plants, for example, use a biological clock with timing that differs from a 24-hour cycle to adjust to changing seasons.
How Does Circadian Rhythm Affect Sleep?
Circadian rhythm is a term that is often used in the context of sleep. The sleep-wake cycle is a prime example of how important circadian rhythms are. During the day, exposure to light causes the internal clock to generate signals that help us stay awake and active. As night approaches, the internal clock triggers the production of melatonin, a hormone that promotes sleep, and then continues sending signals to help us stay asleep throughout the night. This way, circadian rhythms help us align our sleep and wakefulness with day and night, creating a stable cycle of restorative rest that enables increased daytime activity.
What Happens When Your Circadian Rhythm Is Off?
When the body’s natural sleep-wake cycle, also known as the circadian rhythm, is disrupted, it can lead to serious sleep troubles. A disturbed circadian rhythm can cause difficulties in falling asleep, frequent awakening throughout the night or inability to sleep as long as desired in the morning. This can result in reduced total sleep time, and the quality of sleep can become shallower, fragmented, and lower in quality.
Studies have also found that circadian rhythm disruptions can contribute to obstructive sleep apnoea (OSA), which is a sleep disorder characterized by repeated lapses in breathing. OSA reduces the body’s oxygen levels and causes several sleep interruptions through the night. In general, a misaligned circadian rhythm can affect sleep negatively in many ways, increasing the risk of insomnia and excessive daytime sleepiness. Given that sleep plays an essential role in productivity and overall health, the consequences of a disrupted circadian rhythm can be significant.
What Can Disrupt Circadian Rhythm?
Circadian rhythm can be disrupted in both short and long-term periods. Based on their characteristics and causes, experts have identified several types of circadian rhythm sleep-wake disorders (CRSWD).
Jet lag disorder
This disorder occurs when a person travels across multiple time zones within a short period. Until a person’s circadian rhythm adjusts to the day-night cycle of their new location, they may experience sleeping problems and fatigue from jet lag.
Shift work disorder
Work obligations can significantly disrupt a person’s circadian rhythm. Shift work, which requires working through the night and sleeping during the day, can put a person’s sleep schedule in direct conflict with the local daylight hours.
Advanced sleep phase disorder
This rare type of disruption causes people to feel tired early in the evening and wake up very early in the morning. People with this disorder usually cannot stay up later at night or sleep later in the morning, even if they want to.
Delayed sleep-wake phase syndrome
This circadian rhythm disruption is associated with staying up late at night and sleeping in late in the morning. The exact cause of this disorder is still unknown, but it may be related to genetics, underlying physical conditions, or individual behaviour.
Non-24-hour sleep-wake disorder
This disorder mostly occurs in blind people who cannot receive light-based cues for their circadian rhythm. Although their body follows a 24-hour cycle, 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. This disorder is often associated with conditions that affect the brain, such as dementia or traumatic brain injury.
Some circadian disruptions are related to individual behaviour, such as travel or work, which can make sleep-wake schedules inconsistent with normal daylight hours. Other disorders stem from an underlying issue that causes an inability to receive or process environmental cues that regulate the body’s biological clock. In certain situations, genetic causes may be involved, or the cause may be unknown.
How to Maintain a Healthy Circadian Rhythm?
To entrain your 24-hour sleep cycles, follow these healthy sleep tips:
- Keep a consistent sleep schedule.
- Exercise daily.
- Avoid caffeine after noon.
- Limit light exposure before bed.
- Keep naps short and early in the afternoon.
- Create a sleep-friendly bedroom environment.
