You’ve probably noticed that your body naturally feels more awake during certain times of the day and sleepier during other times. For example, many adults feel alert in the late morning, experience an energy slump in the afternoon, and feel sleepy again in the time leading up to bed. None of this is coincidental; instead, it’s the result of our circadian rhythms and their influence on circadian sleep.
Research into circadian rhythms tells us that we are all influenced by an internal biological clock. This clock regulates our circadian rhythms, which are then responsible for everything from our hunger cues to our hormone function, body temperature, sleep-wake cycle, and more.
While maintaining each of these functions is important, circadian sleep (aka a healthy sleep-wake cycle) is especially critical. That’s because a regular sleep-wake cycle is crucial for everything from hormone and immune system function to cognitive and mental wellbeing. And when these cycles get out of whack, it may result in a host of negative consequences.
Convinced that it’s time to care about circadian sleep? Then read on to learn more about circadian rhythms, sleep-wake cycles, and how to promote the healthiest sleep possible.
Note: The content on Sleepopolis is meant to be informative in nature, but it shouldn’t be taken as medical advice, and it shouldn’t take the place of medical advice and supervision from a trained professional. If you feel you may be suffering from any sleep disorder or medical condition, please see your healthcare provider immediately.
What Are Circadian Rhythms?
If you’ve ever researched how to sleep better, then you’ve probably come across the idea of circadian rhythms. But being familiar with the term and actually understanding the concept behind it are two different things.
Put simply, “circadian rhythms” is an umbrella term that refers to a series of physical, mental, and behavioral changes that occur on a cycle throughout each day. Most living things—from humans and animals to plants and microbes—experience circadian rhythms. Most people operate on a circadian cycle that is just around 24 hours.
Circadian rhythms are responsible for daily changes in a variety of bodily processes, from body temperature to blood pressure, alertness, hunger, metabolism, and hormone production (including the production of the sleep hormone melatonin). These rhythms are influenced by a variety of factors ranging from genes to a person’s lifestyle.
When we talk about circadian sleep, we’re talking about the circadian rhythms that relate specifically to sleep. These rhythms are produced naturally within the body, but a wide range of factors can influence their regularity. Circadian sleep rhythms, for example, are heavily influenced by exposure to light and darkness. As you’ll see below, other factors may also affect circadian sleep.
Circadian rhythms are often confused with the idea of biological clocks—but they’re not quite the same thing. Instead, biological clocks are responsible for stimulating and regulating circadian rhythms.
A person’s biological clocks are made of up tiny proteins that interact with the body’s cells and influence the rhythms of tissues, organs, and so on. These proteins are regulated by what researchers refer to as “the master clock” (aka the suprachiasmatic nucleus, or SCN)—a collection of thousands of neurons in the brain that is responsible for syncing up all of the body’s biological clocks.
Because the master clock is in charge of all of the body’s biological clocks (which then produce circadian rhythms), it probably comes as no surprise that the master clock has a role to play in circadian sleep.
Its primary role in sleep involves controlling the production of melatonin, a potent sleep hormone. When the body is exposed to light, the master clock processes this cue via the eyes and then calls for the production of less melatonin. When it seems like darkness is setting in, the master clock will call for the release of more melatonin. As melatonin increases in the body, that communicates to the brain that it’s time to start heading toward sleep.
If your eyes are glazing over from all that biology, take heart: The next few sections will be a straightforward look at the factors that influence circadian sleep, why circadian sleep matters, the most common circadian rhythm sleep disorders, and how to promote healthier sleep-wake cycles.
What Factors Influence Circadian Sleep?
Despite the importance of consistent circadian rhythms, many factors can throw off the balance that keeps these rhythms functioning optimally. Here are just some of the elements that may influence circadian sleep:
- Genetics. For the most part, people and non-human animals all possess a gene that helps regulate the body’s internal clock and support circadian sleep. But in some cases, people or animals may lack this gene, or the gene may become mutated. When this happens, it can severely disrupt sleep-wake cycles.
- Light exposure. For those people who do possess an internal-clock-regulating gene, this gene works together with sunlight exposure to maintain a steady cycle of approximately 24 hours. Exposure to natural light during the day helps keep these rhythms on track. Studies suggest that when people are not exposed to sunlight every day, their circadian rhythms start to shift.
- Age. It’s not uncommon for a person’s circadian rhythms to change as they age. For example, odds are good you have a different sleep-wake cycle as an adult compared to the one you had as a teenager.
- Jet lag. If you’ve ever traveled halfway around the globe, then you don’t need us to tell you that air travel can seriously disrupt your body’s normal sleep-wake routine. That’s because it takes a while for our bodies to catch up to an abrupt change in time zones; even if the surrounding environment suggests it’s time to be awake, your body may still be running on programming that says it’s time to sleep (or vice versa). Jet lag is such a potent circadian rhythm disruptor that in some cases it’s classified as a circadian rhythm sleep disorder. (More on those below.)
- Shift work. Another common culprit when it comes to disrupting circadian sleep is shift work. (Much like jet lag, long-term stints of shift work may also fall under the category of circadian sleep disorder.) Working night shifts can throw off the body’s internal clock, because night shift forces the body to be awake when it would normally want to sleep and to sleep when it would normally want to be awake.
- Alcohol consumption. Research suggests as little as two glasses of wine can interfere with sleep. (Consuming beer and liquor has also been linked to sleep disturbances.) When we don’t sleep properly through the night, this throws off our circadian rhythms.
- Blue light exposure. More and more research suggests exposure to the type of light emitted by electronics (such as smartphones, computers, TVs, tablets, and so on) can interfere with our body’s sleep-wake cycle. That’s because blue light suppresses our body’s production of the sleep hormone melatonin. So if we expose ourselves to blue light in the hours leading up to bed, our body is less likely to receive cues that it’s time to head to sleep.
- Meal and exercise schedules. When we choose to eat and exercise may influence our body’s sleep-wake cycle. For example, exercising right before bed has a stimulating effect, which can delay the onset of sleepiness. Similarly, eating large or hard-to-digest meals right before bedtime may also delay the onset of sleep.
It’s important to be aware of these factors, because each of them has the capacity to throw off your circadian rhythms. That’s no good, because healthy circadian rhythms are critical for enjoying high-quality sleep. We’ll touch more on the benefits of this sleep in the next section.
What Are the Benefits of Healthy Circadian Sleep?
When our circadian rhythms are operating at their best, this significantly increases the chances that we’ll enjoy sufficient, high-quality sleep on a regular basis. That’s important, because a healthy sleep-wake cycle is essential for our bodies and minds to continue functioning optimally. Here are just some of the benefits of circadian sleep:
- It may sustain endocrine system function. As noted above, research suggests circadian rhythms play a big role in regulating hormone production and, by extension, the overall function of the endocrine system. When our circadian rhythms are in balance, we’re more likely to sleep better thanks to proper production of the sleep hormone melatonin.
- It may support immune system function. Studies have found that healthy sleep promotes better immune system responses. This can reduce the risk of infection and speed up healing times when infections do occur.
- It may sustain the healthy function of most other bodily systems. Healthy circadian sleep doesn’t just support the endocrine and immune systems; it also supports virtually every other system in the body. This includes the respiratory system, the digestive system, the cardiovascular system, and so on.
- It may reduce the risk of chronic illness. Largely because healthy sleep is necessary for immune system function, there’s strong evidence that regularly obtaining adequate, high-quality sleep can reduce the risk of a wide variety of chronic diseases. These health conditions include Alzheimer’s disease, dementia, diabetes, heart disease, Huntington’s disease, and Parkinson’s disease.
- It may support cognitive function. Adequate, high-quality sleep promotes greater cognitive function in the form of enhanced creativity, decision-making, and problem-solving skills. Not only that, but it may also help stave off degeneration in the brain.
- It may support mental health. More and more research suggests a number of factors relating to circadian rhythms may influence mental health. For example, adequate amounts of sleep and exposure to sunlight—both of which relate to circadian rhythms—are associated with upticks in positive mood and greater mental health overall. This may help explain why people with mood disorders (including bipolar disorder, depression, and seasonal affective disorder) are more likely to have irregular circadian rhythms.
What Risks are Associated with Not Getting Healthy Circadian Sleep?
When our circadian rhythms are off kilter, this can result in a cascade of issues, from run-of-the-mill sleep deprivation to a full-blown circadian rhythm sleep disorder. (We’ll touch more on the most common circadian rhythm sleep disorders below.)
No matter the cause of a person’s sleep deprivation, the failure to enjoy adequate, high-quality sleep can have several negative consequences. For example, sleep deprivation is associated with the following ill effects:
- It impairs cognitive function, including memory formation, creativity, decision-making, and problem-solving skills.
- It increases the risk of being in an accident at work, on the road, and anywhere else.
- It impairs mental health and increases the risk of anxiety and depression.
- It increases the risk of developing serious health conditions including heart disease, diabetes, heart attack, stroke, high blood pressure, and so on.
- It increases the chances of weight gain and makes it harder to lose weight.
- It speeds up signs of aging, especially in the skin. Chronic sleep deprivation is even associated with a higher risk of mortality overall.
In addition to provoking sleep deprivation and its many negative consequences, there’s some evidence irregular circadian rhythms may themselves increase the risk of various health conditions including bipolar disorder, depression, diabetes, and seasonal affective disorder. If you feel like you may be suffering from any of these conditions, it’s best to consult a healthcare professional immediately.
What Are the Most Common Circadian Sleep Disorders?
When a person’s circadian rhythms are routinely out of sync, this may be a sign that they’re suffering from a circadian rhythm sleep disorder.
(Again, if you feel you may be suffering from any of the above or below conditions, please consult with a medical professional immediately.)
While the cause and manifestation of these disorders may vary, for the most part they produce the same negative consequence. Symptoms of circadian rhythm sleep disorders may include:
- Trouble falling asleep
- Trouble staying asleep
- Feeling tired even after sleeping
If left unchecked, these symptoms can result in persistent fatigue that causes negative ramifications for a person’s physical and mental health and degrades performance at work, school, or home.
Certain people may be more prone than others to developing a circadian sleep disorder. This includes:
- People with certain medical conditions including Alzheimer’s disease, chronic pain, chronic obstructive pulmonary disease, congestive heart failure, dementia, hyperthyroidism, and Parkinson’s disease
- People who take certain medications, such as amphetamines, asthma medication, steroids, and selective serotonin reuptake inhibitors (SSRIs)
- People who have recently experienced a major change in their usual routine
- People who regularly participate in shift work, particularly working night shift
- People who travel overseas
Different sleep disorders may manifest in different ways. Here are some of the most common circadian rhythm sleep disorders:
- Advanced Sleep Phase Disorder. This disorder is characterized by unusually early bedtimes (between 6 and 9 p.m.) and unusually early morning wakeups (between 2 and 5 a.m.). It’s most common among elderly adults and can produce insomnia and/or daytime fatigue.
- Delayed Sleep Phase Disorder. People suffering from Delayed Sleep Phase Disorder tend to have unusually late bedtimes (typically after 2 a.m.). Unless they can make up this sleep by snoozing until the afternoon, people with this sleep disorder tend to experience excessive daytime sleepiness that can impair their performance on the job, at school, and so on. This disorder is most common in adolescents and young adults.
- Irregular Sleep-Wake Disorder/Circadian Sleep Wake Disorder. As the name implies, this disorder is typically characterized by a sleep-wake pattern that is totally irregular. People with this disorder may struggle to sleep for lengthy periods of time and may find themselves drawn to napping several times throughout the day. Because it’s so challenging to sleep for longer periods, people with this disorder may suffer from extreme sleepiness.
- Jet lag. As noted above, jet lag arises when a person’s biological clock is not aligned with their local environment. This can make it difficult to function properly in a different time zone—at least until the body adjusts to that time zone. Studies suggest jet lag is more severe when people travel east in comparison to traveling west.
- Narcolepsy. Narcolepsy represents a disruption in the body’s normal circadian rhythms in several ways. For starters, it’s characterized by excessive daytime sleepiness—even when a person already had adequate amounts of sleep during the night. It’s also marked by uncontrollable bouts of falling asleep during the day—again, in spite of enjoying adequate amounts of sleep at night.
- Non-24-Hour Sleep-Wake Disorder. As a general rule, the brains of people with this sleep disorder have trouble identifying the lighting cues that so strongly influence circadian sleep. This can result in irregular sleep patterns, such as going to bed later and later until a person’s body prompts them to fall asleep during the day instead of at night. The disorder is most common among people with blindness, dementia, and intellectual disabilities.
- Shift work disorder. As noted above, shift work can severely interfere with a person’s natural circadian rhythms. When people work night shift or they work different shifts on a regular basis, it can disrupt their body’s sleep-wake cycle and make it challenging to enjoy adequate amounts of sleep. This recurrent pattern of insufficient sleep can result in excessive fatigue.
If you suspect you might be experiencing a circadian sleep disorder, it’s important to consult a medical professional. They’ll make a diagnosis via a combination of several protocols, such as the use of sleep diaries or overnight sleep tests.
For people who are diagnosed with a circadian sleep disorder, potential treatments will depend on the severity of their disorder, how much it’s interfering with their daily life, the type of disorder, and so on. The most common treatment options include behavior therapy (which involves maintaining regular daily routines, avoiding stimulants, and so on), bright light therapy (which can help promote or delay the onset of sleep), and/or medication (such as melatonin supplements or the short-term use of sleeping pills).
How to Promote Circadian Sleep
Now that you understand why circadian sleep is important, it’s time to make it a priority. Here are some tips for upping your chances of enjoying healthy circadian sleep:
- Maintain a regular sleep routine. Climbing into bed and setting the alarm for the same time every day increases the chances that your body will synchronize to a standard sleep-wake cycle. Try to go to sleep and wake up within 30 minutes of the same time every day, even on weekends.
- Get some sunlight. Enjoying natural sunlight exposure during the day helps maintain your body’s circadian rhythms. For best results, aim to spend some time in bright outdoor light (or at least sit near an open window) in the earlier half of the day.
- Stay active. Regular exercise has been shown to help sustain healthy sleep-wake cycles. So if you needed one more reason why it’s important to exercise on a daily basis, this is it. Aim to squeeze in activity every day, whether by taking a lunchtime stroll or hitting the gym before work. Just try to avoid working out in the last few hours before bed, as this can have a temporary stimulating effect that makes it harder to fall asleep.
- Minimize light exposure at night. From high-powered overhead lighting to the blue light emitted by electronic devices such as smartphones or TVs, nighttime light exposure can interfere with our body’s production of the sleep hormone melatonin. This, in turn, can make it harder to drift off to sleep. To increase your odds of falling asleep at a healthy time, aim to minimize light exposure in the evening hours by avoiding electronics use, dimming the lights, and/or investing in blue light blockers.
- Avoid stimulants in the hours leading up to bed. Stimulating activities can take several forms, from drinking caffeine to smoking cigarettes, working right up until bedtime, exercising right before bed, or having intense conversations before trying to fall asleep. Try to avoid these activities in the hours leading up to bed and opt for a restful routine instead.
- Practice good sleep hygiene. This primarily revolves around creating a bedroom environment that is conducive to sleep. For example, it’s a good idea to make sure you’re sleeping in an environment that is dark, cool, and quiet. Reserve the bed for nothing but sleep and sex, and remove electronics, work, clutter, and stressful conversations from the bedroom.
Circadian rhythms may sound like a vague, scientific concept, but the truth is they impact us every day. In order to sustain healthy hunger cues, hormone function, sleep-wake cycles, and more, it’s essential that we take the time to understand and support our body’s circadian rhythms. Emphasizing circadian sleep is a surefire way to help sustain your body’s natural rhythms and enjoy the many benefits that a healthy sleep-wake cycle has to offer.