What is the circadian rhythm?
The Circadian Rhythm
An internal timing mechanism that regulates our daily biological processes.
Our circadian rhythm determines when we are most active during the day, when we get hungry, when we wake up, and when we feel tired. It plays a fundamental role in maintaining health and well-being, so much so that disruptions in the circadian rhythm can lead to numerous health problems, including sleep disorders, depression, and obesity.
The Importance of the Circadian Rhythm
The circadian rhythm is regulated by the body's "master clock," located in the center of our brain, in the suprachiasmatic nucleus. This clock sets the timing of various biological and chemical processes across the 24-hour cycle of the day, responding to changes in environmental light.
Environmental light is the most important external factor controlling the circadian rhythm. When light hits the retina, it signals the suprachiasmatic nucleus to adjust the sleep-wake cycle to track day and night changes. For example, morning light signals the body to increase cortisol levels, which helps with waking up and increased activity, while the fading light in the evening triggers melatonin production to promote sleep.
Nearly every living organism that lives for more than a few days has a circadian rhythm designed to synchronize our own functioning with the Earth's rotation, as it causes alternating periods of light and darkness. This rhythm is pre-programmed and repetitive, which is clearly observable in how it regulates our body temperature.
As bedtime approaches, our body temperature drops, reaching its lowest point about two hours after falling asleep, but this process also begins if we stay awake all night. Our circadian rhythm doesn’t stop; at the usual time, the suprachiasmatic nucleus sends signals and turns down the "thermostat." That's why the same temperature in the evening feels cooler.
Morning Larks & Night Owls
Everyone has a circadian rhythm, but the peaks and troughs within the 24-hour cycle can vary.
Some people feel alert early in the day and therefore get tired earlier and go to bed sooner. These individuals are called morning larks and make up about 40% of the population. They enjoy waking up at dawn and generally function best during those early hours.
Another large group are the "night owls," who prefer staying up late and getting up later. They can be active even when morning larks have long been asleep. They constitute roughly 30% of the population (the remaining 30% are intermediate types who don’t like waking up too early or too late).
Studies have shown that the prefrontal cortex region of night owls' brains—which is responsible for higher-level thinking, logical reasoning, and emotional regulation—is in "offline" mode during early morning hours. This means they need much more time to reach their normal operating state. Such individuals are often mistakenly labeled as lazy because they can’t get up on time, but it’s not their fault. Whether someone is a morning lark or a night owl is encoded in their DNA.
Most societies have fixed work schedules—including school routines—that favor early risers, which disadvantages night owls. They aren’t able to perform at their best during the morning hours and lose the opportunity to shine in the afternoon, when they’re really at their peak, because work hours end. Additionally, night owls tend to suffer from greater sleep deprivation as they are forced to wake early but tend to fall asleep later.
Due to sleep deprivation, night owls are at higher risk of illnesses such as depression, anxiety, diabetes, cancer, heart attacks, and strokes. These individuals can maximize their potential and protect their health best by choosing work that aligns with their circadian rhythm.
No Coincidences
There are important evolutionary reasons for the division between night owls and morning larks! When we lived in smaller tribal communities, this ensured the community was protected or supervised for the least amount of time possible. The "owls" stayed awake late to keep watch, and the "larks" took over early in the morning.
The Impact of Circadian Rhythm on Health
Synchronizing the circadian rhythm and the sleep-wake cycle is essential for physical and mental health. Disruptions to this rhythm—such as shift work, frequent time zone changes from travel, or inappropriate light exposure—can contribute to sleep disorders, metabolic diseases, cardiovascular problems, and mood disorders.
Suggestions for Synchronizing Your Circadian Rhythm
Proper Light Exposure: Try to expose your eyes to plenty of natural light during the day, especially in the morning, to help set your biological clock.
Consistent Sleep Schedule: Aim to go to bed and wake up at the same time every day, even on weekends.
Avoid Late-Night Screen Time: The blue light from screens can disrupt melatonin production, making it harder to fall asleep.
