What Is Your Circadian Rhythm? Here's How It Impacts Your Sleep, Health, and Life
Your internal clock plays a big role in your physical and mental health—sleep experts explain how it works.
Fact checked by Haley Mades
It may seem instinctual that humans understand when to go to sleep, wake up, and eat, and while this is true to some extent, we can thank our circadian rhythm for sending these life-sustaining cues. Our circadian rhythm is a (roughly) 24-hour internal “clock” in our bodies that plays a major role in our physical and mental health, both affecting and affected by multiple organ systems (and even all the way down to individual cells). Here’s how your circadian rhythm works, and how to honor and support your unique sleep-wake cycle to feel your best.
Related: This Is How Much Sleep You Need Every Single Night, According to Experts
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What is your circadian rhythm?
Christina Pierpaoli Parker, PhD, licensed clinical psychologist who is board-certified in behavioral sleep medicine, calls a circadian rhythm the body’s “central pacemaker” that “regulates our sleep timing.”
Everyone is born with the ability to develop a circadian rhythm. It typically develops in humans around the two-to-three month mark, which helps explain why newborns’ sleep schedules don’t distinguish much between day and night. Once established, your circadian rhythm regulates cycles of alertness and sleepiness by responding to external stimuli, primarily light changes, in your environment. Therefore, when it’s dark out, you begin feeling sleepy, and when the day breaks, you start to wake up.
Without a circadian rhythm, humans would sleep in a disorganized fashion and lack a general understanding of day and night. Not only would our sleep be erratic, but we also "would not be able to optimize energy expenditure and the internal physiology of the body," explains a research article on physiology and circadian rhythm.
How does it affect your health and life?
Your alertness, sleepiness, appetite, and even body temperature are all impacted by your circadian rhythm. “Our knowledge about circadian rhythm now tells us that the wake-sleep cycle is an integral part of human health,” says Sudha Tallavajhula, MD, sleep neurologist and medical director at TIRR Memorial Hermann Neurological Sleep Medicine Center. “All other organ systems function in response to wakefulness and sleep.”
Circadian rhythm disturbance or interference can have any number of health-related ripple effects throughout your body and its vital systems, including your immune system, digestive system, different hormone systems (like reproductive and endocrine), and cardiovascular systems, to name a few.
Critical bodily functions also align themselves to the rhythm of day and night, Dr. Tallavajhula explains, and this is all thanks to our circadian rhythm. “For example, your kidneys reduce urine output at night, so that your sleep is not disrupted,” she says. “Many hormones like steroids, which help us function during wakefulness, are also minimized during sleep.”
Why does understanding your circadian rhythm matter?
It’s no secret that good quality sleep is essential to overall health, influencing everything from memory and mood, to immune system strength, to even your blood pressure. If we didn’t sleep according to the cues sent by our circadian rhythm, what might happen? Trying to sleep at a “suboptimal circadian time,” Pierpaoli Parker says, can impact sleep quality and sleep architecture, or the basic phasic structure of normal, healthy sleep.
When this happens, Pierpaoli Parker explains that people can develop an increased risk of diseases such as diabetes, hypertension (high blood pressure), and even cancer. Not only does our circadian rhythm help us understand when to sleep and eat, but it plays an important role in keeping us healthy and disease-free long term.
Related: 11 Healthy Habits That Can Help You Sleep Better
What affects your circadian rhythm?
Staying on track with a consistent sleep schedule is often easier said than done. Changing time zones, work shifts, and inevitable stress can throw your circadian rhythm, or your internal clock, off balance. Other times, influencing factors can be as small as our habits and surroundings. Light emitted from artificial sources, Pierpaoli Parker says, can disrupt your circadian rhythm. These blue light sources include smartphones, computers and TV, which is why many sleep experts recommend avoiding their use near or at bedtime.
Related: Those Blue-Light Glasses Aren’t Doing Much for Your Eyes, Study Finds
Genetic conditions that affect your brain or hormones can also cause circadian rhythm disorders. Evening caffeine consumption can delay the onset of your natural circadian rhythm as well, so if you’re craving a mug of something before bedtime, consider enjoying a cup of caffeine-free herbal tea instead of green tea, black tea, coffee, or espresso. Lastly, a room that’s too bright may signal to your body that it’s not time for sleep, even if it’s technically night out. Blackout curtains can help in this regard, as can wearing a sleep eye mask if your room has too much light pollution.
The Best Ways to Support Your Circadian Rhythm
While it may be a natural process, there are steps you can take to support your circadian rhythm and honor your body’s natural sleep-wake needs. This can allow you to work with your body to feel your best and stay as healthy as possible. Pierpaoli Parker recommends implementing the following lifestyle changes—or good sleep hygiene practices—for optimal circadian rhythm balance and support.
Only go to bed when you feel truly sleepy, not just tired (i.e. avoid naps when possible—though they can be helpful in some cases when kept on the shorter side and not taken too late in the day).
Keep as consistent a wake-up time as possible, even on weekends.
Attempt to get 10 to 30 minutes of natural light upon waking.
Follow a consistent bedtime routine.
Take a warm bath or shower before bed (this warms up, then subsequently cools down your body temperature—this temperature drop helps promotes sleep).
Opt for a book instead of TV or prior to sleep.
Avoid smartphone/laptop/TV use in bed.
With a sleep-promoting bedtime routine and regular wake times, you can help keep your circadian rhythm balanced - and ultimately reap the many health benefits it can offer.
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