What is the Body's Circadian Rhythm

What is the body's circadian rhythm?

The body's circadian rhythm, often called the "biological clock," is a natural, internal process regulating various physiological and behavioural processes over a 24-hour cycle. It plays a crucial role in coordinating the body's sleep-wake cycle, hormone production, metabolism, and other essential functions to align with the Earth's day-night cycle.

Awareness and management of circadian rhythms improve your daily performance. According to research, you should be:

• Highly alert at 10 am.

• Best Coordination at 2.30 pm.

• Fasted Reaction Time 3.30 pm.

• Greatest Cardio Vascular Efficiency & Muscle Strength 5 pm.

• Highest Blood Pressure 6.30 pm.

• Sleep Hormone Starts To Secret 9 pm.

Are you performing to maximum efficiency?

The circadian rhythm is influenced by the suprachiasmatic nucleus (SCN) in the hypothalamus. The SCN receives input from light-sensitive cells in the eyes, which helps synchronise the body's internal clock with the external environment. Here are some critical aspects of the circadian rhythm:

1. Sleep-Wake Cycle: One of the most well-known aspects of the circadian rhythm is the sleep-wake cycle. The circadian clock regulates the release of the hormone melatonin, which helps induce sleepiness in the evening and decreases in the morning, promoting wakefulness.

2. Body Temperature: The circadian rhythm affects body temperature, making it warmer during the day and cooler at night. This temperature variation can influence sleep patterns and alertness.

3. Hormone Production: Various hormones, such as cortisol, growth hormone, and insulin, exhibit circadian rhythms in secretion. Cortisol levels typically peak in the early morning, helping to promote wakefulness and energy. At the same time, growth hormone release often occurs during deep sleep.

4. Metabolism: The circadian rhythm also plays a role in regulating metabolism. It influences how the body processes and stores energy, affecting factors such as hunger, digestion, and energy expenditure.

5. Cognitive Function: Cognitive abilities, such as alertness, concentration, and memory, are influenced by the circadian rhythm. Peak mental performance usually aligns with times of increased wakefulness.

6. Mood and Emotions: Disruptions to the circadian rhythm can impact mood and emotions. Irregular sleep patterns and disturbances in the biological clock have been linked to mood disorders such as depression and bipolar disorder.

7. Shift Work and Jet Lag: When the circadian rhythm is disrupted by factors such as shift work or rapid time zone changes (jet lag), individuals may have difficulty adjusting to new sleep-wake patterns and experience sleep disturbances, fatigue, and impaired performance.

Why Is The Circadian Rhythm Important?

Maintaining a consistent circadian rhythm is essential for overall health and wellbeing. Irregularities in the biological clock, such as those caused by irregular sleep schedules or exposure to artificial light at night, can disrupt hormone balance, affect sleep quality, and potentially contribute to health issues like obesity, diabetes, skin tone, and cardiovascular problems.

To support a healthy circadian rhythm, experts advise maintaining regular sleep patterns, exposing oneself to natural light during the day, and creating a sleep-conducive environment at night. Additionally, understanding the importance of the circadian rhythm can help individuals make informed decisions about when to engage in various activities to optimise their physical and mental performance.

How to reset the circadian rhythm

Resetting your circadian rhythm, the internal 24-hour clock that regulates your sleep, energy, hormones, digestion, and overall wellbeing, requires a combination of consistent habits, strategic exposure to natural cues, and the removal of behaviours that confuse your body's biological clock.

The most powerful and scientifically supported method is controlling light exposure, because light is the master signal your brain uses to determine whether it is time to be awake or asleep.

To reset your rhythm, expose yourself to bright natural sunlight within the first 30–60 minutes of waking, ideally by stepping outside rather than staying indoors near a window. Morning light tells the brain it is daytime, suppresses melatonin, and sets a timer for sleepiness to return about 14–16 hours later.

In the evening, do the opposite: reduce exposure to bright light, especially blue light from phones, tablets, and televisions, at least two hours before bed. Darkness triggers the release of melatonin, the hormone that helps you drift into restful sleep.

Along with proper light management, going to bed and waking up at the exact times every day, including weekends, is crucial, as irregular sleep schedules confuse the internal clock. Your body thrives on routine; even a one-hour shift can throw off your hormones, hunger cues, mood, and concentration the next day. Another critical factor is optimising your behaviour during the hours leading up to bedtime:

• Avoid heavy meals.

• Caffeine.

• Intense exercise.

• Emotionally stimulating activities at night.

These raise cortisol or increase alertness when your body should be winding down. Instead, develop a predictable wind-down routine:

• Dim the lights.

• Read a book.

• Stretch gently.

• Practice slow breathing.

These cues signal to the brain that sleep is approaching and help stabilise the rhythm. Physical activity during the day, especially in the morning or early afternoon, also helps reset the circadian system by reinforcing the difference between day and night.

Refreshing your sleep environment is equally important; keep your bedroom calm, dark, and quiet, and reserve the bed only for sleep so your brain associates that space with rest rather than wakefulness. Avoid naps longer than 20–30 minutes, as late-day naps, exceptionally long ones, can shift your sleep window later.

Food timing also plays a role: eating meals at consistent times helps synchronise your internal clocks, especially those in the gut and liver, which communicate closely with your main circadian centre. Avoid eating large meals late at night, as your metabolism naturally slows down in the evening.

Suppose your sleep schedule is severely disrupted, such as due to night shifts, travel, or prolonged insomnia. In that case, you may need to adjust your rhythm in small increments, shifting bedtime earlier or later by just 15–30 minutes per day.

This gradual approach prevents the body from resisting the change. Stress management also matters; chronic stress and high cortisol can disrupt sleep signals, so practices like:

• Meditation.

• Breathwork.

• Journaling.

• Evening relaxation rituals, Hot Bath or Shower.

Help bring your body into the calm state needed for consistent rest. With the right combination of light management, consistent timing, healthy habits, and a supportive environment, it is absolutely possible to reset your circadian rhythm and restore the natural energy, clarity, and mood that come from a well-aligned internal clock.

Final Thoughts

In today's modern world, with all its technology and electronic entertainment, we are constantly surrounded by the beeping and flashing of phones and other devices. It's no surprise that our basic biological need for sleep is being affected.

This constant presence of technology reminds me of New York, the city that never sleeps, a place where everything is available 24/7. During my first visit in my early twenties in the 1980s, I would be lucky to get two hours of sleep each day; that might even be an exaggeration. We were stimulated and anxious about missing out, as there was always something happening. It’s pretty similar to the digital world we experience today. After our three-day adventure in New York, we were both exhausted and unable to function, confused, irritable, and tired, yet we couldn't find a way to sleep.

See Blog, The Importance of Sleep