What Is Circadian Rhythm?
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Medically reviewed by Rafle Fernandez, MD
A circadian rhythm is a natural process that regulates your body's sleep and wake patterns, among other key functions. It's often described as an internal clock that operates on a roughly 24-hour cycle, influencing when you sleep, wake, eat, and more.
Even a slight disruption to your daily routine on a regular basis can make you—and your body—feel out of sorts. Shifting some habits can help you reset your circadian rhythm. You can also reach out to a healthcare provider for other treatment options, including medications and supplements.
How Does Circadian Rhythm Work?
Circadian rhythms are internal cycles that rise and fall over a period of 24 hours, primarily in response to light and dark. These cycles help manage some of your body's processes related to daily activities, including sleeping and waking. It's most well known as the sleep-wake cycle`.
Circadian rhythms are driven by a "control center" in your brain: a cluster of nerve cells that coordinate signals received from visual cues in your environment. For example, exposure to morning sunlight tells your body it's time to wake up and start your day. A setting sun prompts the release of melatonin, a hormone that promotes sleep.
Your circadian clock is most sensitive to light at certain times:
About two hours before your typical bedtime
During the night
About one hour after your typical waketime
Your energy naturally shifts throughout each 24-hour cycle. Wakefulness tends to decrease at certain times of the day:
2 a.m.-5 a.m.
2 p.m.-5 p.m.
12 a.m.-2 a.m.
However, circadian rhythms vary from person to person. Your circadian rhythms are influenced by genetics, in addition to external factors and routines.
For example, some people prefer to go to bed and wake up early because they feel more alert and active earlier in the day. Other people prefer to go to bed and wake up later because they feel more alert and active during the second half of the day.
The Importance of a Circadian Rhythm
Sleep is crucial for physical and mental functioning. For example, it restores and builds-up energy, helps you learn and store memories, and builds immunity. Maintaining a stable sleep-wake cycle is essential for functioning well.
Circadian rhythms also affect other bodily functions. They help regulate:
The release of hormones
Digestion and appetite
Body temperature
Alertness and reaction times
Circadian rhythms influence metabolic health, including cholesterol and blood sugar regulation. They can also affect your risk of certain mental health conditions, including depression.
What Can Affect Circadian Rhythms?
Changes in your environment, as well as internal factors, can desynchronize (shift the timing of) your circadian rhythm.
These triggers include:
Sunlight: The amount of natural light exposure you receive each day affects the timing of your internal clock. Spending more time in natural light energizes you.
Caffeine: Consuming this stimulant, particularly later in the day or in the evening hours, can interfere with your sleep-wake periods.
Jet lag: Traveling across time zones impacts your sleep schedule, including how and when your body produces melatonin.
Shift work: A work day that starts and ends at irregular times—especially over the course of a long period of time—can shift your internal clock.
Electronic device light: Exposure to blue light, as well as white light (which contains blue light), within two hours of bedtime can make it difficult to fall and stay asleep. This artificial light can disrupt your sleep cycle and performance. Blue light radiates from screens like televisions, computers, and cell phones. Red, orange, and yellow light has minimal or no effect on circadian rhythm.
Daylight saving time: Any shift in a 24-hour cycle—even by one hour—can desynchronize your circadian rhythm.
Visual impairment: The brain perceives light through sight in order to cue circadian rhythm processes. This can be difficult for people with visual impairments.
Medications: Certain types of medications, as well as when you take them, can disrupt your circadian rhythm.
It takes time to readjust your circadian rhythm, which is why traveling to another time zone or starting a job with different hours can feel jarring. For example, some parents of infants and young children gradually adjust bedtime in the week leading up to daylight savings to prevent disrupting sleep schedules.
What Happens if Your Circadian Rhythm Is Disrupted?
Schedules continually shift, and it can be difficult to maintain a stable circadian rhythm. You will probably adjust to some fluctuation here and there. However, frequent disruption can negatively affect your health.
Sleep disorders connected with disrupted circadian rhythms include:
Delayed sleep-wake phase syndrome (DSPS): Going to bed at least two hours later than what is considered normal bedtime
Advanced sleep-wake phase syndrome (ASPS): Going to bed several hours earlier than what is considered normal bedtime
Shift work sleep disorder (SWD): Symptoms like insomnia (difficulty falling or staying asleep, or low-quality sleep) and excessive fatigue connected to working more evening and/or early morning hours (between the hours of 6 p.m.-7 a.m.)
Non-24-hour sleep-wake rhythm disorder (N24HSWD): A condition in which your sleep-wake cycle gets progressively later each day
Jet lag disorder: Symptoms like excessive sleepiness, difficulty sleeping, and gastrointestinal discomfort due to travel across multiple time zones
Other possible complications include:
Night eating syndrome (NES), a condition characterized by high-calorie consumption in the evening and during the night, which has been linked to weight gain and depression
Diabetes, when the body resists or doesn't produce enough insulin
Cardiovascular disease, an umbrella term that refers to several conditions that affect the heart and its blood vessels
Mental health disorders like depression and bipolar disorder
Seasonal affective disorder, a type of depression brought on by the change of seasons
People who work irregular hours and night shifts might be at a higher risk for developing these conditions.
What Are the Signs?
While you might feel more tired some days, certain signs suggest that your circadian rhythm is negatively affecting your health.
Signs that you might need a reset include:
Difficulty falling or staying asleep
Feeling excessively tired or exhausted
Difficulty focusing or concentrating on tasks
Unusual aches, pains, or stomach discomforts
How To Reset Your Circadian Rhythm
Irregular sleep patterns can interfere with your health and your quality of life. Fortunately, you can take steps to realign your circadian rhythm.
Lifestyle Habits
The following lifestyle habits can help you shift to a more stable circadian rhythm:
Follow a relaxing bedtime routine to help yourself wind down physically and mentally.
Avoid screens at least two hours before bedtime.
Try blue light glasses when using screens.
Establish a consistent bedtime and try to stick to it, even on the weekends.
Create a healthy sleep environment. Sleep in a cool, dark, and quiet room.
Avoid napping during the day if possible, or limit naps to 30 minutes or less.
Exercise daily. Try not to exercise too close to bedtime, as this can make falling asleep more difficult.
Limit caffeine and alcohol intake, particularly in the evening hours.
Light Therapy
Your circadian rhythms respond to sunlight exposure. Exposing your eyes to natural light, as well as some types of artificial light, at certain times of the day can help reset your sleep-wake clock.
Here are some suggestions:
Morning sunlight: Get bright sunlight exposure first thing in the morning, if possible, to help you feel more awake. This will also help you fall asleep more quickly at bedtime.
Less time with screens and artificial light: Be mindful of screen time and indoor (artificial) light exposure, particularly before you plan to go to sleep.
Bright light therapy: Light therapy products include light boxes, desk lamps, light visors, and dawn simulators. Your healthcare provider might recommend spending a particular amount of time using a product like this—for example, 45-60 minutes daily.
Supplements and Medications
If lifestyle shifts don't seem to be helping you resynchronize your internal clock, you may want to reach out to a healthcare provider about other treatment options.
Treatment options include:
Melatonin supplements: These supplements can work as aids to help you fall asleep.
Melatonin medication: This can help treat sleep disorders like non-24-hour sleep-wake rhythm disorder.
Sleep-promoting medications: Medications like benzodiazepines (a class of depressant medications) can cause drowsiness and promote restful sleep.
Wake-promoting medications: Medications like Provigil (modafinil) and Nuvigil (armodafinil) can prompt alertness during the work day, particularly for shift workers.
Dietary supplements are minimally regulated by the FDA and may or may not be suitable for you. The effects of supplements vary from person to person and depend on many variables, including type, dosage, frequency of use, and interactions with current medications. Please speak with your healthcare provider or pharmacist before starting any supplements.
A Quick Review
Your body's natural circadian rhythms dictate much of your daily functioning from the time you fall asleep to the time you wake up. Disruptions to these patterns can lead to poor quality sleep and other health conditions.
Things like getting enough natural light exposure and incorporating healthy sleep hygiene habits can help you reset a disrupted circadian rhythm.
Each person's internal body clock is unique, and your genes play a role in whether you're naturally a night owl or an early bird. Be patient with yourself as you try to stabilize or modify your circadian rhythm.
Reach out to a healthcare provider if your sleep-wake schedule is interfering with your daily life or if you think you might benefit from shifting your circadian rhythm. A healthcare provider can give you recommendations or refer you to a sleep specialist.
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