Circadian Rhythm

What Is Circadian Rhythm?

Through millions of years, life has been shaped by the world’s rhythmic shifts of night and day. Many living things—including plants, animals, and humans—have circadian rhythms, which are tailored to life on earth and the changes that occur as the planet rotates on its axis. Every 24 hours, predictable shifts in light and temperature take place. Circadian rhythms help living things respond to changes in their environment Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source in ways that conserve energy, help them find food, and allow them to grow and heal. 

In humans, circadian rhythms serve many functions, Trusted Source UpToDate More than 2 million healthcare providers around the world choose UpToDate to help make appropriate care decisions and drive better health outcomes. UpToDate delivers evidence-based clinical decision support that is clear, actionable, and rich with real-world insights. View Source including helping regulate :

• Sleeping and waking
• Core body temperature
• The immune system
• Hormones
• Metabolism
• Cognitive function
• The body’s reaction to stress

How Do Circadian Rhythms Work?

Circadian rhythms are controlled by biological clocks located in organs and glands throughout the body, but all of these peripheral clocks are commanded by a “master clock” in a region of the brain called the suprachiasmatic nucleus.

In most adults and adolescents, this master clock operates on a cycle that is slightly longer than 24 hours. In order to maintain alignment with the 24-hour rotation of the planet, the master clock must adjust by about 12 to 18 minutes every day. For this reason, it times circadian rhythms according to environmental cues known as “zeitgebers,” German for “timekeepers.”

Light and darkness are the most important and powerful zeitgebers. Other zeitgebers involved in circadian timing Trusted Source UpToDate More than 2 million healthcare providers around the world choose UpToDate to help make appropriate care decisions and drive better health outcomes. UpToDate delivers evidence-based clinical decision support that is clear, actionable, and rich with real-world insights. View Source include :

• Meals
• Exercise
• Social interactions
• Daily routines Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source
• Stress

These zeitgebers trigger the release of hormones in the brain and the delivery of chemical signals to body tissues. Thus, the master clock Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source is able to effectively time vital body functions, such as the conversion of food into energy, fluctuations in body temperature, and when a person feels like sleeping or waking up.

“An adult’s natural internal clock is on average 24.2 hours. We use external stimuli to help entrain this rhythm daily to 24 hours. Changing the amount and times of sunlight exposure, or changing our routines, can send signals to our ‘master clock’ and shift our natural circadian rhythms.”

Dr. Lulu Guo

Sleep Medicine Physician

The Link Between Sleep & Circadian Rhythm

Circadian rhythms play a vital role in a person’s ability to sleep in one consolidated block of time at night and to stay up for roughly 16 hours straight every day. Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source As the sun sets in the evening, the brain begins producing melatonin, a hormone that induces sleepiness. Core body temperature also drops, Trusted Source UpToDate More than 2 million healthcare providers around the world choose UpToDate to help make appropriate care decisions and drive better health outcomes. UpToDate delivers evidence-based clinical decision support that is clear, actionable, and rich with real-world insights. View Source contributing to decreased alertness.

These changes, driven by circadian rhythms, combine with sleep drive to cause a person to fall asleep at night. In the morning, as exposure to light increases, melatonin production stops and body temperature rises, promoting wakefulness.

Sleep is most likely to be refreshing and restorative when circadian rhythms, the natural cycle of daylight and darkness, and sleep patterns align.

What Happens If Your Circadian Rhythm Is Off?

If you don’t sleep when your body tells you that it’s time to—or if you sleep for long periods during the day—your circadian rhythms might become misaligned with the 24-hour cycle of day and night. Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source There are many reasons why this might happen, including shift work, travel across time zones, social or study habits that lead to irregular bedtimes, illness, stress, frequent sleep disruptions, or a noisy and bright sleep environment.

Misalignment between your circadian rhythms and your environment, especially over the long term, can have serious consequences for your health and wellbeing. 

• Sleep problems: Misaligned circadian rhythms can make it harder to fall asleep at bedtime, lead to more wake-ups during the night, and result in less sleep overall. Misalignment can first be confused as insomnia but frequent misalignment can in fact  contribute to the development of insomnia.
• Performance issues: If your circadian rhythms are off, you are likely to experience a range of issues that affect your ability to function, such as excessive sleepiness, difficulty focusing, memory problems, and difficulty performing high-precision tasks.
• Emotional and social difficulties: Sleep deprivation makes it harder to manage stress and to regulate emotions, so if your circadian rhythms are out of sync, you’re more likely to experience mental health struggles like depression and conflict in your relationships.
• Accidents and errors: Misaligned circadian rhythms increase your risk of having a car accident, making a serious mistake at work, or getting hurt on the job.
• Health problems: A range of health problems are associated with out-of-sync circadian rhythms, including obesity, diabetes, heart attacks, high blood pressure, and cancer.
• Fatigue: Chronic misalignment of circadian rhythms or a lack of a routine to help entrain the internal clock can cause symptoms of low energy and grogginess.

“Sleeping at the right times is just as important as the number of hours of sleep.”

Dr. Lulu Guo

Sleep Medicine Physician

Circadian Rhythm Sleep Disorders

There are six sleep disorders that can cause abnormalities in a person’s ability to sleep and wake in expected 24-hour patterns. Some of these disorders are environmental in nature or “extrinsic,” meaning that they happen when a person’s activities or circumstances cause their circadian rhythms to desynchronize from their environment. Other disorders are “intrinsic”—that is, they happen when a person’s circadian timekeeping system doesn’t function properly. 

• Shift work disorder: This disorder occurs when shift work prevents a person from sleeping according to their natural circadian rhythms. People with this disorder often struggle to stay awake during night shifts and to sleep at home during the day, which results in sleep deprivation. There is further disruption as many shift workers change sleep schedules throughout the week depending on if they are working or not working.
• Jet lag disorder: When people travel across multiple time zones, their circadian rhythms won’t initially align with the light-dark cycle in their new environment. This can result in jet lag, which causes daytime sleepiness, digestive problems, and sleep difficulties.
• Advanced sleep-wake phase disorder: Individuals with this disorder feel sleepy before their desired bedtime and wake up very early in the morning. Sleep debt occurs when people with this disorder force themselves to stay up late, as they are unable to sleep in.
• Delayed sleep-wake phase disorder: People with this disorder don’t feel ready for bed until very late at night, and they struggle to get up at conventional wake times. They would sometimes feel a “second wind” in the evening and this pattern is frequently labeled as being a “night owl”. This can result in sleep loss for people with work, school, or family obligations in the morning.
• Non-24-hour sleep-wake rhythm disorder: In people with this disorder, the master clock driving circadian rhythms fails to make the daily corrections that align it with the 24-hour day. Their internal clock may shift by a few minutes or hours every day, making it difficult to maintain a routine and  sleep at night or stay awake during the daytime.
• Irregular sleep-wake rhythm disorder: For individuals with this disorder, sleeping and waking are not governed by circadian rhythms. As a result, sleep tends to happen in short intervals interspersed throughout the day without a clear pattern.

How To Maintain a Healthy Circadian Rhythm

Following sleep hygiene guidelines can help ensure that your sleep-wake cycle aligns with your circadian rhythms. 

• Maintain a regular schedule. To the extent that it is possible, eat your meals, go to bed, and wake up at the same time every day. 
• Implement a bedtime routine. Choose one to three relaxing activities, like taking a warm bath or stretching, and do them before bed every night.
• Exercise. Get regular physical activity during the daytime.
• Avoid naps late in the day. Naps, especially in the late afternoon, can interfere with your ability to fall asleep at bedtime.
• Avoid screens and bright light before bed. Light, particularly blue light produced by electronic devices, can inhibit melatonin production—so it’s important to avoid light exposure when you’re trying to wind down.
• Enjoy sunlight during the day. In the morning, open the curtains, and if you feel tired during the day, spend a few moments outside.

If you are a shift worker or you have travel plans, talk to your doctor about how to minimize misalignments between your circadian rhythms, your sleep schedule, and your environment.

How To Fix a Disrupted Circadian Rhythm

Many people experience disruptions to their circadian rhythms at some point in their lives. If your circadian rhythms are out of sync with your environment, there are several approaches that might help you bring them back into alignment.

• Light therapy: This common treatment for disrupted circadian rhythms involves strategically timed exposure to light and darkness. Controlling exposure to light can alter melatonin production and shift sleep and wake times earlier or later. This is often accomplished through the use of a light box or light-blocking glasses. 
• Melatonin supplements: In some circumstances, melatonin supplements are an effective way to induce sleepiness at appropriate or desired times. Correct timing and dose of melatonin is important to help adjust the circadian rhythm effectively. This strategy can help travelers advance their bedtimes and may help individuals with certain circadian rhythm disorders adjust their sleep schedules. 
• Sleep schedule adjustments: Strategic adjustments to your sleep schedule may help realign your circadian rhythms. If you are a shift worker, implementing a consistent sleep schedule, even on your off days, may help. If you are a traveler, gradually adjusting your sleep schedule in small increments can help you minimize the effects of jet lag.
• Medications: In some cases, your doctor might recommend using medications to induce sleep or promote wakefulness. However, these medications can pose risks and may have undesirable side-effects, so they are often a second-line treatment for disrupted circadian rhythms and circadian rhythm sleep disorders.

Before beginning any therapy intended to realign your circadian rhythms, make sure to talk to your doctor about your symptoms and treatment plans.

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