Have you had trouble sleeping recently or staying awake at the right times? To figure out the solution to your sleep disturbances, it is essential to understand how and what regulates sleep in the first place. At the core of these processes lies the circadian rhythm—the natural patterns that affect many processes in the body, including your mental state and sleep pattern.
Continue reading our article as we explain the circadian rhythm, how it works, and what factors influence its balance.
What is Circadian Rhythm?
Now, what is circadian rhythm, exactly? It is an internal biological clock that regulates physical, mental, and behavioral changes over 24 hours. In humans, almost every tissue and organ has a circadian rhythm. Together, they regulate the body’s day and night cycles.
In regards to the sleep-wake cycle, circadian rhythms play a critical role in cueing the body to produce melatonin—a hormone that promotes sleep—when the sun is out while suppressing its release during daylight to wake you up. Besides that cycle, this rhythm also plays important parts in other biological functions such as:
- Digestion and Metabolism: This regulates appetite, digestive efficiency, and metabolic processes, which are higher during the day when energy demands are higher due to your daily activities.
- Temperature Regulation: For you to be able to sleep, your body temperature should be in a comfortable range, which is lower. In contrast, to induce wakefulness, your temperature should be higher. This rhythm controls these two processes, too.
- Hormone Release: In addition to melatonin, cortisol and the human growth hormone follow the circadian rhythm. Cortisol peaks in the morning to boost energy, while the growth hormone is mainly released during deep sleep.
The Role of the Suprachiasmatic Nucleus (SCN)
SCN is a group of nerve cells in the hypothalamus of the brain that controls circadian rhythms. It integrates various time cues, known as ‘zeitgebers‘ (German for “time givers”), to synchronize biological processes earlier throughout the day.
The most powerful time cue is the light, which directly influences the SCN. However, other factors, such as physical activity, social interactions, eating, and stress, also play a role in keeping the time in check.
How Does Circadian Rhythm Work?
Circadian rhythm responds to ‘time givers’, especially light exposure. After the light or other environmental cues are detected by your body, it will send signals to the master clock, the SCN itself. Then, the SCN sends signals to other parts of the brain that control the sleep-wake cycle, eating habits, digestion, body temperature, and energy use.
The Sleep-Wake Cycle
As it gets dark, the body clock signals the pineal gland to produce melatonin and gradually lower the body temperature. These two create an optimal state for falling asleep and maintaining restful sleep. In the morning, exposure to light and other environmental cues triggers melatonin suppression and increases body temperature, which signals us to wake up.
However, the circadian rhythm also plays a major role in how we sleep through different stages of sleep:
- Non-REM Sleep: This stage consists of light and deep sleep stages in the early night, which are crucial for physical restoration and tissue repair. Circadian rhythms ensure that non-REM sleep aligns with the first part of the night, when the body temperature is at its lowest and melatonin levels are highest.
- REM Sleep: The REM stage, characterized by the occurrence of dreams (good or bad) and heightened brain activity, is essential for cognitive functions, such as memory consolidation. This stage occurs in the rising phase of body temperature and the lowest point of melatonin production, suggesting it is largely controlled by circadian rhythm.
What Affects Circadian Rhythm?
Environmental Factors
Light is the most significant factor, as around 20,000 nerve cells respond to it. Exposure to bright light during the day reinforces wakefulness and aligns the body clock with daylight hours. In contrast, exposure to artificial light at night, such as digital screens, can disrupt melatonin production, disturbing the sleep-wake cycle.
Temperature also regulates rhythms. Cooler temperatures at night cause the body temperature to drop, signaling the body to sleep. Hence, significant changes such as overly warm nights or unusually cold days can disrupt the body’s ability to maintain normal rhythm, making it harder to sleep.
Noise exposure can also affect sleep quality by increasing the duration of light sleep stages, making it harder to achieve deep, restorative sleep. Chronic exposure to noise, especially during the night, has also been linked to poor sleep efficiency and heightened levels of stress hormones like cortisol.
Lifestyle Factors
Unsurprisingly, irregular sleep can disrupt your body’s circadian rhythm. Frequent changes in bedtime or wake-up time confuse the master clock, delaying melatonin release and disturbing the natural sleep-wake cycle. However, if you consistently experience an irregular sleep schedule, feeling sleepless at night and excessively sleepy during the day, it may be time to consult a sleep doctor.
Another lifestyle factor that influences circadian rhythm is exercise. Morning or afternoon workouts align well with the body’s natural clock. However, a vigorous one close to bedtime may raise body temperature and delay melatonin production, disrupting sleep. Hence, it is generally advisable to keep your exercise moderate and finish at least 2–3 hours before bedtime to minimize any potential effects on your circadian rhythm.
Travel and Shift Work
When discussing circadian rhythm, we also have to talk about jet lag. If you wonder what causes your restlessness each time you travel, it stems from a mismatch between your body’s internal clock and the local time at your destination. Your circadian rhythm remains aligned with the time zone of your departure, causing feelings of fatigue, insomnia, or daytime sleepiness. Luckily, jet lag gradually corrects itself as your internal clock adjusts to the new schedule.
Imagine the occasional mismatch happening daily, as it does for night shift workers. Irregular work hours—such as five days of night shifts followed by a regular sleep-wake cycle on weekends to spend time with family—can be extremely disorienting for the circadian rhythm. The constant dyssynchrony does not allow the body enough time to adjust, leading to insomnia or sleep deprivation.
Health Conditions
Two common sleep conditions, insomnia (difficulty falling asleep, staying asleep, or both) and sleep apnea (repeated interruptions in breathing due to various conditions during sleep), can interfere with the body’s ability to establish a consistent sleep-wake cycle. However, the relationship with the circadian rhythm can go both ways for insomnia. While insomnia disrupts the sleep-wake cycle, a disorder in the rhythm can also contribute to insomnia.
The last factor worth mentioning is age. You may not realize it, but your circadian rhythm changes as you age. After puberty, the internal clock shifts about two hours later than in childhood. This shift remains until adulthood and shifts to become earlier as you grow older.
The Importance of Maintaining a Healthy Circadian Rhythm
After learning about circadian rhythm, it is clear how vital it is to maintain a healthy internal clock. In the short term, a well-aligned circadian rhythm improves sleep quantity and quality and boosts energy levels to power you through your day. Over the long term, maintaining this balance can help prevent serious health issues.
How to Support a Healthy Circadian Rhythm
1. Establish a Consistent Sleep Schedule
If you can, follow a consistent sleep routine. Stick to your schedule night by night, even on weekends, because a slight shift to your sleep-wake cycle can, in the long run, throw off your body clock.
2. Create a Relaxing Bedtime Routine
Our circadian rhythm picks up habits through the repetition of specific cues. Creating a relaxing bedtime routine gives external cues to your body block that it is time to sleep. In response, it will instruct the body to make you sleepy.
3. Limit Screen Time Before Bed
When discussing what circadian rhythm is, we learned that light is the most significant ‘time giver’. This light includes the blue light emitted by screens, which can trick your body’s clock into thinking it is still daytime. Limiting screen time before bed can signal your body that it’s time to wind down and improve overall sleep quality.
4. Optimize Your Sleep Environment
Optimize your sleep environment by ensuring your bedroom is completely dark, cool, and quiet. Even in a busy area, you can block those lights and noise using blackout curtains and earplugs.
5. Adjust Gradually to Time Zone Changes
When traveling across time zones, you will most likely experience jet lag. To minimize its effects, it’s important to adjust gradually. A few days before travel, shift your sleep, wake times, and mealtime by 1–2 hours closer to the destination’s time zone. These gradual adjustments make it easier for your body to adapt to the new schedule and maintain a healthier circadian rhythm.
How WISH Can Help with Circadian Rhythm Issues
Whether you’re dealing with jet lag, night shifts at work, or an out-of-the-ordinary sleep/wake cycle, WISH sleep coaches are here to help you identify and address disruptions in your circadian rhythm. Through personalized consultations, we will assess factors affecting your off-balance circadian rhythm and use evidence-based strategies to create tailored plans that may include environmental modifications or pharmacological changes if needed to realign your circadian rhythm.
Book your appointment with us today to achieve better sleep quality and overall well-being.
