Your body runs on an internal time clock. This clock affects sleep, hormone levels, digestion and cognitive function. While research is still occurring regarding biological rhythms, disruptions to our biological rhythm can result in heightened risk for sleep disorders, depression, obesity, diabetes, and cardiovascular disease.
According to research at the National Institute of General Medical Sciences, in most cases, these cycles follow a typical 24-hour time schedule, determined by both light exposure and lifestyle factors.
Unfortunately, with increased exposure to screens, late-night shifts, and irregular habits, more people have rhythm-related health problems than ever before—often without them knowing.
What is Circadian Rhythm?
Circadian rhythm is a natural, biological process that supports the body's ability to remain regulated throughout a roughly 24-hour cycle. This rhythm is regulated by the suprachiasmatic nucleus of the brain (SCN), which is located in the hypothalamus. The internal biological clock acting as the basis for circadian rhythms can be easily influenced by outside cues, including light and darkness.
Circadian rhythms are not just about sleep. They influence:
- Energy levels throughout the day
- Metabolism and digestion
- Heart rate and blood pressure
- Mental alertness and mood stability
- Cell regeneration and immune response
How Does it Work?
The circadian clock is your body's internal clock that is controlled by a master clock located in the hypothalamus - called the suprachiasmatic nucleus (SCN).
The SCN receives light and dark signals from the eyes and interprets those signals to manage important physiological processes like hormone secretion, body temperature, metabolism and the sleep-wake cycle.
In the morning, when light is present, the SCN suppresses melatonin (the sleep hormone), activates cortisol (the waking hormone) and gets your body moving in preparation for daytime activity.
At night, melatonin production occurs, initiating the signal for rest and repair. The process is repeated roughly every 24 hours and is important to resynchronizing each day by external signals such as sunlight, physical activity, and meals.
On the cellular level, clock genes are switched on and off in a rhythmic pattern in nearly every organ responsible for biological timekeeping.
The SCN is the master clock however, peripheral oscillators in the heart, liver, and digestive tract can also adapt to behavioral instructions regarding our meals and sleep schedules which helps them sync their rhythms to the master rhythm and/or disconnect.
Circadian Rhythm Across Life Stages
In Babies, Toddlers, and Children
Newborns lack a complete circadian rhythm when they’re born. They sleep in cycles typically shorter than 24 hours, and they do not have a means of differentiating between night and day.
Usually between 6 and 12 weeks, babies begin to develop their internal clocks in relation to the outside world, having a series of regular events (like light exposure, feeding routines, sleep times, etc.).
Facultatively, most toddlers and younger children tend to have earlier circadian phases and will wake up and go to sleep earlier than adults. In this phase of sleep, daylight, and regular routines at bedtime are crucial for promoting their sleep habits.
In Teenagers
The circadian rhythm shifts to a later hour during adolescence. This is called "sleep phase delay." Teens are typically more alert later in the evening and want to wake up later in the morning, which is often a conflict to the early start time of school.
While this biological shift is completely normal, it can lead to chronic sleep deprivation if teens are required to wake up early. The lack of morning light and increased behavior on screens at night can disrupt the adolescent's circadian rhythm again.
In Adults
Most adults have a stable circadian rhythm, with a circadian cycle that includes waking during the day and sleeping at night.
Despite this rhythm, shift work, traveling across time zones, too much screen time, poor sleep hygiene, as well as aging can lead to disruptions in our natural rhythm.
Aging adults over 60 may struggle with a gradual phase advance that results in feeling sleepy earlier in the evening and waking earlier in the morning due to changes in melatonin release and light sensitivity.
What will trigger the Circadian Rhythm?
Your circadian rhythm is influenced by both environmental cues and internal biological processes. These triggers help regulate your sleep-wake cycle, body temperature, hormone release, and more.
Main Triggers of Circadian Rhythm:
- Light exposure (especially natural sunlight)
- Sleep-wake timing
- Meal schedules
- Physical activity
- Social interaction
- Environmental temperature
- Melatonin release due to darkness
Circadian Rhythm Disorders
Delayed Sleep Phase Disorder (DSPD): Individuals who have DSPD naturally feel tired much later in the night (e.g., 2–4 AM) and prefer waking later in the day. DSPD is more common in adolescents and young adults, and it can sometimes negatively impact school or work obligations.
Advanced Sleep Phase Disorder (ASPD): The opposite of DSPD, ASPD individuals feel sleepy during early evening hours (e.g., 6–8 PM) and wake up early in the morning. ASPD is more common in older adults.
Irregular Sleep-Wake Rhythm: Unspecified has no consistent sleep pattern. Sleep occurs though multiple naps over a 24-hour period, instead of consolidated overnight sleep. This can commonly occur in individuals with neurodegenerative disorders like dementia.
Non-24-Hour Sleep-Wake Disorder: Mainly affects individuals with no light perception, as their internal clock receives no light input. Therefore, they gain a sleep period progressively later each day and their sleep period becomes desynchronized from the 24-hour day.
Shift Work Sleep Disorder: Affects individuals who have work schedules that are not fixed, and they are required to work at night. Disruption to the body's normal sleep and wake cycle results in insomnia, fatigue, and impaired alertness.
Jet Lag Disorder: Occurs when travelling quickly across time zones (especially west to east). The body remains linked to the original time zone and, through time, sleep problems and fatigue are exhibited.
Effects of a Disrupted Circadian Rhythm
When circadian rhythm is disrupted—from lifestyle, environment, or medical conditions—it can involve nearly every major bodily system. Here are some ways disruption can impact your wellbeing:
1. Sleep Issues
- Insomnia or difficulty falling and staying asleep
- Daytime sleepiness or fatigue
- Poor sleep quality and reduced REM sleep
2. Mental Health
- Increased risk of depression and anxiety
- Mood swings and irritability
- Cognitive decline and difficulty concentrating
3. Physical Health
- Weakened immune function
- Elevated risk of obesity, type 2 diabetes, and cardiovascular disease
- Hormonal imbalances (cortisol, melatonin, insulin, etc.)
4. Digestive Problems
- Irregular appetite and food cravings
- Disrupted metabolism
- Higher likelihood of gastrointestinal disorders
5. Performance and Productivity
- Reduced alertness and reaction time
- Poor memory retention and decision-making
- Impaired motor coordination
How to Monitor Circadian Rhythm?
Monitoring your circadian rhythm involves clinical assessments and diagnostic tools that give you an objective view of your internal clock. These are used when sleep disorders or disruptions are suspected:
Actigraphy
A small wrist-worn device (actigraph) tracks your movement over several days to estimate sleep-wake cycles. It’s used to diagnose circadian rhythm disorders like delayed sleep phase disorder.
Polysomnography (Sleep Study)
This overnight sleep test records brain waves, oxygen levels, heart rate, breathing and body movements. It will tell you if disruptions in your circadian rhythm are causing insomnia or hypersomnia issues.
Core Body Temperature Monitoring
Body temperature follows a circadian pattern. Measuring core temperature over 24–48 hours will show you abnormalities in rhythm timing and amplitude.
Dim Light Melatonin Onset (DLMO) Test
These methods are typically recommended when lifestyle tracking isn't enough or when a circadian rhythm disorder is suspected. A sleep specialist or neurologist can guide appropriate testing and treatment.
Salivary or Blood Melatonin Tests
Frequent sampling (every hour or two in dim light) can track melatonin throughout the evening and night to see where melatonin production is disrupted.
Sleep Questionnaires & Diagnostic Interviews
Clinicians may use standardized questionnaires like the Morningness-Eveningness Questionnaire (MEQ) or the Munich Chronotype Questionnaire (MCTQ) to assess sleep habits and rhythms.
These are usually recommended when lifestyle tracking isn’t enough or when a circadian rhythm disorder is suspected. A sleep specialist or neurologist can guide testing and treatment.
How to Control Your Circadian Rhythm?
Enhancing your circadian rhythm can lead to improved sleep, increased concentration, and overall health. You cannot reset your clock overnight, but daily practices and environmental cues can help naturally reset it.
1. Stay Consistent with Your Sleep Schedule
Try to go to bed and wake up at the same time daily, even on weekends, to reinforce your internal clock.
2. Get Morning Sunlight Exposure
Natural light is the strongest cue for your circadian rhythm. Aim for at least 15–30 minutes of sunlight exposure in the morning.
3. Limit Artificial Night Light
Avoid screens and bright lights at least an hour before bed to allow melatonin levels to rise as naturally as possible.
4. Make a Consistent Bedtime Routine
Calming activities such as reading, meditating, or taking a warm shower can help signal your brain to slow down and prepare for sleep.
5. Avoid Caffeine and Heavy Meals Late in the Day
Caffeine and heavy meals can delay sleep onset and alter your natural rhythm if consumed too close to bedtime.
6. Use Your Day to Be Active
Regular physical activity, preferably during the first half of the day, is associated with better, deeper sleep and enhances circadian stability.
7. Control Stress
Stress is a part of life, and constant bad stress, along with frequent cortisol spikes, can disrupt your rhythms. Deep breathing, mindfulness, or yoga-based practices can help you keep your stress regulated.
8. Sleep in a Cool, Dark Environment
Sleeping in a room that is dark, quiet, and cool (60-67°F or 15-19° C) will keep you sleeping uninterrupted and aligned to your rhythms.
When to Consult with a Doctor?
You should think about seeing a health care provider if:
- You have had difficulty falling asleep or staying asleep for more than two weeks.
- You have had daytime fatigue, brain fog, or changes in your mood that are starting to disrupt your life.
- You believe you have made reasonable and sustainable changes to your environment and lifestyle, but still feel your sleep-wake cycle is off.
- You suspect and have experienced symptoms of a circadian rhythm disorder or sleep disorder that might include insomnia, delayed sleep phase, or non-24-hour sleep-wake disorder.
- You are experiencing difficulties sleeping in conjunction with anxiety, depression, or other mental health symptoms.
- You work night shift or have other irregular hours and are struggling with sleep loss issues.
The sooner you seek help, the less likely you are to long-term issues and improvements in quality of life will be possible through appropriate diagnosis, therapy, or medication if necessary.
Final Thoughts
Your circadian rhythm is vital in health and wellness, but it influences everything from sleep to mental clarity to hormones. Disrupting your internal clock—whether through lifestyle, work, or health condition—can influence your physical health and emotional wellness.
Learning how your circadian rhythm works and recognizing imbalance to manifest physical or emotional disturbances allows you to take simple and effective steps to restore your body back into rhythm.
Making sleep a priority and ensuring you seek medical attentiveness in a timely manner to serve your overall well-being is an important step to bettering your sleep and, subsequently, your daily functions and performance.
