We might not fully realize that our lives are regulated by circadian rhythms (the natural sleep-wake schedule in the brain). Experts believe that nearly every tissue and organ has its own 24-hour rhythm, all working in sync with the day and night cycle. What are circadian rhythms? They are physical, mental, and behavioral changes the body experiences over a 24-hour cycle. This rhythm depends on light and darkness, but it’s also influenced by meal schedules, physical activity, social environment, air temperature, and even stress. And it’s not just us; every living creature operates according to its own circadian rhythm.
Circadian Rhythms Rule Us
Circadian rhythms affect important functions in the human body, including sleep patterns, hormone release, appetite, digestion, and body temperature. The so-called biological clock controls these rhythms. "It consists of proteins encoded by thousands of genes that turn on and off in a specific sequence. The master clock coordinates all biological clocks in the body," explain scientists from the National Institute of General Medical Sciences (NIGMS) in the USA.
The human master biological clock is located in the brain, specifically in the suprachiasmatic nucleus. This region is responsible for releasing melatonin, the hormone that helps us fall asleep. Melatonin production is directly linked to the amount of light entering our eyes. The suprachiasmatic nucleus also oversees the release of two other hormones related to circadian rhythms: cortisol (which keeps us awake) and adenosine (which induces sleepiness at night, though it starts accumulating in the morning).
Circadian Rhythm Disruptions
For thousands of years, we lived in tune with the day and night cycle (light and darkness). Today, however, our biological clock is constantly disrupted by artificial light, including that emitted by electronic devices, as well as by shift work or, for example, traveling across time zones. Additionally, illnesses, especially neurological disorders, and certain medications can disrupt circadian rhythms. Genetics also plays a role.
Circadian rhythm disruptions are associated with serious health risks. Prolonged sleep deprivation and continuous disturbances to these rhythms increase the risk of obesity, diabetes, mood disorders, heart issues, high blood pressure, and even cancer. Lack of sleep can also exacerbate existing conditions and lead to fatigue, difficulty concentrating, and learning problems.
Wake-up Time and Health
The time you go to bed and wake up matters. It’s important to maintain a consistent sleep-wake schedule because regularity can improve sleep quality and stabilize your circadian rhythm. Why is it beneficial to go to bed and wake up at the same time each day? This practice is linked to better sleep quality, as it helps balance the proportions between REM sleep (rapid eye movement sleep) and deep sleep (NREM or slow-wave sleep).
Additionally, it impacts the release of hormones such as melatonin (which helps us sleep) and cortisol (which helps us wake up). If our circadian rhythm is out of balance, we risk hormone imbalances, including hunger hormones, reduced cognitive performance, alertness, and productivity, and mood disorders like depression or anxiety. Sleep quality also influences disease susceptibility, as it affects the immune system. Sleep studies conducted at Stanford Medicine a few years ago showed that both early risers and late sleepers who stay up late have higher rates of mental health disorders, including depression and anxiety.
What’s the best time to wake up? Generally, it depends on individual preferences, lifestyle, circadian rhythm, and your chronotype ("night owls" vs. "early birds"). However, following general guidelines is recommended, such as ensuring you get enough sleep (adults should aim for 7 to 9 hours of sleep). Consistency, meaning a regular sleep schedule, is also important. It seems best to wake up when it’s already light outside. Exposure to natural light helps regulate the internal clock and improves mood and well-being.
Sleep experts also emphasize that it’s better to allow yourself to sleep longer in the morning rather than setting an early alarm only to hit snooze and doze off again. Waking up and falling back asleep interrupts the release of several hormones, including cortisol and serotonin, which can confuse the brain and leave you feeling more tired or groggy. Additionally, waking up early isn’t necessarily beneficial for everyone, especially for those who go to bed late. The key remains the length and quality of sleep.
