Timing is everything. When it comes to sleep, that much-quoted truism is especially fitting. Because when you sleep is just as important as how long you sleep. If you have difficulty falling or staying asleep at night or struggle with excessive daytime sleepiness, your circadian rhythm could be off track. And a more chronic or severe case could indicate a circadian rhythm sleep disorder (CRSD).
Your circadian rhythm is a kind of internal body clock that dictates your ideal sleep and wake times during a roughly 24-hour period. Heavily influenced by the natural cycle of light and darkness associated with sunrise and sunset, this rhythm is baked into our human biology. That’s why you function and feel your best when your sleep schedule coincides with your circadian rhythm. Unfortunately, modern life often gets in the way of that alignment.
Circadian misalignment and circadian rhythm disorders were likely not as prevalent among our ancestors who lived before the industrial revolution and the widespread use of artificial lighting. But many of our modern conveniences have caused inconvenient problems when it comes to falling asleep and staying asleep through the night. Being exposed to artificial light at night — especially blue light emitted from the screens of our electronic devices — and jet travel across time zones are two common culprits of circadian disruption. Shift work and erratic sleep schedules are also problematic.
In this article, we’ll discuss the inner workings of your circadian clock, go over the different types of CRSDs, and explain their risk factors, symptoms, and treatment options. We’ll also share sleep hygiene tips that can help you reach and maintain circadian alignment — for better sleep at night and more energy during the day.
The cyclical rhythms of different organisms have been a subject of scientific inquiry for centuries, but sleep did not formally emerge as a topic of research until the 1920s. The term “circadian rhythm” was coined in 1959 by a scientist named Franz Halberg, the father of chronobiology, which is the study of biological rhythms. From the Latin words “circa” (about) and “diem” (day), Halberg formed the word “circadian” after studying and documenting the daily biological rhythms that can tip the scale between health and disease.
Indeed, chronic circadian misalignment has since been linked to increased risk for cardiovascular disease, diabetes, obesity, cancer, depression, and other mental health problems. And healthy circadian functioning promotes restorative sleep, which can help boost the immune system, reduce stress, and improve mood and cognitive performance.
Circadian rhythm is one of the Two Laws of Sleep. Based on sleep scientist Alexander Borbély’s two-process model of sleep regulation, these two laws govern how we feel and function each day. The second law is sleep debt.
Sleep debt is the amount of sleep you’ve owed your body over the past 14 days. It’s a running total of the hours of sleep you’ve missed, compared to the sleep your body needed. High sleep debt is linked to lower cognitive performance and a number of poor health outcomes.
Although these two laws work independently of each other, they are also interrelated. Together, they point you toward your ideal sleep schedule and wake schedule. But problems with either one can negatively impact the other and make it more difficult to get the sleep your body needs. For instance, if your sleep schedule gets thrown off, you may have a hard time getting to sleep, which causes your sleep debt to go up.
Before we get into what can go wrong and the different kinds of circadian rhythm disorders, let’s take a look at how your internal clock works when everything is perfectly aligned.
Your circadian rhythm is driven by a complex biological system that has two main components: the master clock, located in the suprachiasmatic nucleus (SCN), a special group of neurons in your brain’s hypothalamus; and peripheral clocks, located in most tissues and organ systems throughout the body.
Sunlight is the most important external influence on the SCN, which is attuned to the roughly 24-hour cycle of changing light caused by the Earth’s orbit around the sun. In the morning, when the optic nerve senses daylight, the SCN releases cortisol, norepinephrine, and serotonin — hormones that make you feel more alert and awake. At night when it gets dark, the SCN prompts the brain’s pineal gland to produce the sleep-inducing hormone melatonin.
Melatonin helps prepare your body for sleep by lowering body temperature, blood pressure, stress hormones, and alertness. About 2-3 hours before your biological bedtime, your dim light melatonin onset (DLMO) marks the beginning of what the RISE app calls your Melatonin Window. Because this is when your brain produces its highest levels of melatonin, going to bed during this window is your best shot at falling asleep quickly and staying asleep through the night.
The exact time of your DLMO on any given night is unique to you and can be a clue to your chronotype. Determined by age and genetics, your chronotype is an indicator of the length of your underlying circadian rhythm. If you’re naturally an early riser or morning chronotype, your internal clock runs shorter than 24 hours. The internal clock of a night owl or evening chronotype runs somewhat longer. But chronotype is really a spectrum, and where you sit on the spectrum may make you more or less susceptible to circadian misalignment and disorders.
Because most of us lead busy lives with work schedules and family obligations that don’t always line up with our natural circadian rhythm, it’s not unusual for things to go off track. And there are a few things that can be especially disruptive to your biological clock.
Exposing yourself to too much light at night — bright light and blue light in particular — can wreak havoc on your circadian rhythm because light disrupts your body’s melatonin production and makes it difficult to fall asleep. Well-timed light exposure, on the other hand, is a cornerstone of circadian alignment. Ideally, you want to expose yourself to sunlight soon after waking and avoid most light (or wear blue-light blocking glasses) in the 90 minutes before bedtime.
Timing is also important when it comes to substances like alcohol, caffeine, and nicotine. Consuming them too late in the day can make it difficult to fall asleep and stay asleep, which can lead to circadian disruption and increased sleep debt.
Anything that contributes to an irregular sleep-wake schedule is also potentially disruptive. If stress, social jet lag, or health problems make it difficult to keep a regular bedtime and wake time, your risk for misalignment goes way up. And because your circadian rhythm thrives on consistency, major schedule changes brought on by jet lag and shift work can also be incredibly disruptive.
Circadian misalignment and CRSDs have also been associated with certain medications, medical conditions and events (blindness, dementia, Parkinson’s disease, head injury, stroke), and old age.
Common symptoms of CRSDs include difficulty falling asleep, waking up frequently during the night, waking up too early or too late, and persistent daytime fatigue and sleepiness. Some people also develop secondary symptoms such as depression and impaired cognitive performance. There are also specific symptoms, tendencies, and risk factors for different disorders.
A person who regularly goes to bed in the early evening (6 p.m. to 9 p.m.) and wakes up hours earlier than is considered normal (2 a.m. to 5 a.m.) may be suffering from advanced sleep phase syndrome (or advanced sleep phase disorder). The fact that rising before the sun in the very early morning is more common in some families suggests that there is a genetic component to ASPS.
Risk groups: Morning chronotypes, older adults
This disorder is characterized by an undefined sleep-wake cycle. People with ISWRD have fragmented sleep and seem to be lacking a regular circadian pattern. Instead of consolidating sleep at night, they take a series of naps throughout a 24-hour period.
Risk groups: Nursing home residents as well as people with Alzheimer’s, dementia, traumatic brain injuries, intellectual disabilities, and other neurological conditions
As its name suggests, shift work disorder is a disruption in the circadian rhythm brought on by jobs that require employees to work when they would normally be sleeping. It can affect people who work night shifts, early morning shifts, swing shifts, and rotating shifts.
In addition to causing insomnia, on-the-job sleepiness, downgraded performance, and increased accident risk, shift work has been labeled as a “Class 2A carcinogen” by the International Agency for Research on Cancer and the World Health Organization. Over time, working the night shift increases the risk of hormone-dependent cancers, including prostate cancer, breast cancer, and ovarian cancer.
Risk groups: Shift workers, including first responders, health care professionals, transportation workers, factory workers, etc.
Many people find it difficult to adjust to and function in a new time zone, especially after quickly crossing multiple time zones on a lengthy flight. Jet lag disorder is a temporary sleep problem that usually occurs after travel to a destination that’s two or more time zones different from your home. Since most people find it easier to delay sleep than to advance sleep, eastward travel is typically more problematic than westward travel.
Risk groups: Frequent fliers, anyone who travels by air across multiple time zones
Although rare among the sighted, non-24-hour sleep-wake disorder is quite common among blind people whose circadian rhythms do not follow a 24-hour light-dark cycle. Sometimes called free-running (non-entrained) type, this disorder often causes alternating episodes of daytime sleepiness, insomnia, and normal sleep.
Risk groups: Individuals who are totally blind
Although the exact prevalence of circadian rhythm sleep disorders may be underestimated, studies suggest that approximately 3% of the adult population suffers from a CRSD. Because these disorders often share symptoms with other conditions — insomnia, sleep apnea, and narcolepsy for example — diagnosis is best left to a sleep medicine specialist.
To determine whether or not a patient is suffering from a CRSD, doctors often use sleep diaries, sleep studies, and actigraphy.
Actigraphy is a noninvasive technique that measures physical activity levels with a wristwatch-like motion-sensing device that can be worn over an extended period. Data gathered is used to rule out or diagnose a CRSD.
The goal when treating a CRSD is to address and correct the underlying mismatch between the desired timing of sleep and the ability to fall asleep and remain asleep. Treatment options may vary depending on the specific type of CRSD, but many regimens involve one or more of the following.
Maintaining good sleep hygiene — the upkeep of behaviors that influence the way you sleep — is important for all of us.
Good sleep habits are vital for maintaining proper circadian functioning and keeping sleep debt low. So it should come as no surprise that improving sleep hygiene is often the first line of treatment for circadian rhythm sleep disorders. (It may not be enough to correct some disorders, but it’s a step in the right direction.)
With easy to set up daily reminders, the RISE app can help you turn these recommendations into healthy habits. The app will tell you the right timing for each one based on your unique circadian rhythm.
Because light is the most impactful environmental cue for circadian functioning, strategically adjusting the timing of a patient’s light exposure can help correct CRSDs. The specifics of treatment protocols vary depending on the specific disorder, but bright light therapy has proven to be both effective and versatile.
It is used to gradually shift a patient’s sleeping patterns and sleep period back into normal range. A sleep specialist might prescribe 15-90 minutes of exposure to a high-intensity lamp first thing in the morning because light is a signal for the brain to stop producing melatonin. Other guidelines for timed light exposure followed by CRSD patients can be beneficial to all of us:
Chronotherapy is a method of modifying a person’s sleep schedule to resynchronize their underlying circadian rhythm to fit within a more normal or desired timeframe. The idea is to gradually adjust the timing of the biological clock by delaying (for DSPS) or advancing (for ASPS) sleep. The keyword here is ‘gradually.’ Shifting to a new bedtime and/or wake time in small increments (5 - 15 minutes at a time, for example) makes it easier for the body to adapt to a new sleep schedule. (Phototherapy is sometimes considered to be a part of chronotherapy.)
Phototherapy is the best way to support your body’s natural melatonin production, but melatonin supplements are used to treat some cases of circadian rhythm sleep disorders. For DSPS, taking melatonin in the late afternoon or evening can help patients shift to an earlier bedtime. The optimal timing and dosage of melatonin supplements used to treat jet lag disorder and shift work disorder will vary depending on the individual and each specific situation.
Circadian rhythm sleep disorders can make day-to-day functioning a challenge. Fortunately, CRSDs are usually treatable —and your odds of being diagnosed with one are slim.
Circadian misalignment, on the other hand, is much more prevalent. But it is certainly not insurmountable. And preemptively adopting the sleep hygiene and phototherapy recommendations used to treat some CRSDs might be the best way to prevent them or correct more run-of-the-mill circadian misalignment.
Whether you’re looking to maintain circadian alignment or reset your circadian rhythm, we can help. With the RISE app, you will understand and navigate your biological rhythm and turn good sleep hygiene recommendations into actual habits that ensure you’re getting enough sleep to fuel your day.
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