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Biological Clock Day – April 28, 2025

Biological Clock Day is celebrated every April 28 to raise awareness about the circadian rhythm and its impact on our sleep-wake cycle, body system, and mood. Did you know that we practiced segmented sleep in medieval times before the invention of the electric bulb reduced sleeping hours to six hours? The biological clock is linked with the circadian rhythm, a 24-hour cycle part of our internal clock that carries out essential functions and processes, such as regulating the sleep-wake cycle. The circadian rhythms are connected to a master clock located in the brain that sends signals to regulate activity throughout the body. This master clock is influenced by environmental cues, allowing the circadian rhythms to work based on the day and night cycle.

History of Biological Clock Day

Sleep is as much a part of the natural process as eating and breathing. Since the beginning of human evolution, we have always needed sleep. And as we experience changes in civilization, human sleeping patterns also change, impacted by cultural shifts, migration, and technological advancements. Our understanding of how early humans sleep is limited, as there is little to no historical evidence of early hunter-gatherer and agricultural societies. However, by observing hunter-gatherer groups in Tanzania, Bolivia, and Namibia, researchers discovered that early humans only slept for about 6.25 hours and rarely woke up during the night. This sleeping pattern changed when humans migrated to Europe, where they experienced longer nights, leading to segmented rest.

The earliest references to the segmented sleeping pattern were in Homer’s “The Odyssey,” dating back to about 725 B.C. to 675 B.C., and this practice continued into the Renaissance. During the period between the first and second sleep, people socialize quietly, pray, do chores, visit friends, and have sex. This sleeping pattern was most revered during the late Middle Ages and Renaissance. However, all these changed in the 19th century, at the peak of the Industrial Revolution. In 1839, Thomas Edison invented the incandescent light bulb, which led to more extended workdays and a permanent end to segmented rest.

Businesses and people started prioritizing work and productivity over getting a good night’s rest. This increase in working hours led to early labor movements such as the eight-hour movement. In 1926, Ford adopted the eight-hour work and the 40-hour workweek, which became the regulation for all businesses everywhere. Today, people are back to placing reverence on sleep because of its numerous health benefits and impact on productivity. Corporate business people are now using sleep as one of their tools to increase productivity, using periods between meetings and business travels to get that needed nap.

Biological Clock Day timeline

Neolithic Era
Hunter-gatherer Sleeping Patterns

Hunter-gatherer groups sleep for an average of 6.5 hours every night, without interruption.

1300 — 1600
The Height of Segmented Rest

During the late Middle Ages and Renaissance, people spend the time between the two sleep periods having quiet reflection or enjoyment.

19th Century
The End of Segmented Rest

The Industrial Revolution and the invention of the incandescent bulb bring an end to segmented rest.

21st Century
A Productivity Tool

Business people are now using sleep to improve their productivity after learning about its impact on work.

Biological Clock Day FAQs

Can you change your biological clock?

Yes, it’s possible to change your biological clock. First, you need to understand your sleep-wake cycle, set a sleep schedule, and gradually move your bedtime. Exercising, avoiding alcohol and caffeine in the evening, and limiting screen time can help change your biological clock.

What is the biological clock in humans?

The biological clock (circadian rhythm) is a 24-hour cycle affected by light or darkness. It controls our sleep-wake cycle, body temperature, and hormonal production.

How accurate is our biological clock?

Our biological clock is relatively accurate. If exposed entirely to darkness, it will only lose or gain a few minutes.

How to Observe Biological Clock Day

  1. Learn about your biological clock

    Each person has their own internal clock that governs their body functions. Understanding your biological clock can help boost your overall health, prevent weight gain, and improve productivity. You can learn about your biological clock by observing your daily routine or taking the TimeSignature test. The latter requires two blood tests spaced 10 to 12 hours apart. Check your local clinic if the test is available.

  2. Take sleep more seriously

    Sleep offers a world of benefits when given the proper priority. Pushing it down to the least important section of your schedule could lead to drastic implications for your health and relationship. Commit this National Biological Clock Day to start prioritizing sleep more.

  3. Share your knowledge of biological clock

    Are you part of the medical or science community? Or do you happen to be more knowledgeable about the biological clock than the average person? Use that knowledge on National Biological Clock Day to educate people about the circadian rhythms and their importance. You can share this knowledge with your coworkers, friends, or followers on social media.

5 Interesting Facts About Sleep

  1. One-third goes to sleeping

    Humans spend an average of one-third of their life sleeping.

  2. Dreams also come in black and white

    According to research, many people dreamt in black and white before the introduction of colored television.

  3. Dreams don’t last

    Within five minutes of waking up, we forget about 90% of what we dreamt about.

  4. Sleep deprivation kills

    Losing sleep can kill you faster than food deprivation.

  5. Lose sleep, feel more pain

    According to a study, cutting down your sleeping hours can reduce your pain threshold.

Why Biological Clock Day is Important

  1. It’s vital to our overall health

    The biological clock, also known as the circadian rhythm, helps regulate the body’s processes and functions such as the sleep-wake cycle, heart rate, metabolism, body temperature, and hormone levels. A disruption to the circadian rhythms can lead to weight gain, insomnia, poor mental health, and reduced productivity.

  2. Adequate sleep increases productivity

    According to research, losing sleep can diminish your concentration and cognition and reduce your confidence level. Getting enough sleep can potentially improve your problem-solving skills and enhance memory performance. In fact, corporate individuals are now taking advantage of sleep to improve their productivity at work.

  3. Sleep improves social interaction

    Sleep deprivation can lead to issues such as depression and a reduction in our ability to control our emotions and behaviors. Giving sleep a priority in your day-to-day lives can help you build better, healthy relationships and improve your interaction with others.

Biological Clock Day dates

2025April 28Monday
2026April 28Tuesday
2027April 28Wednesday
2028April 28Friday
2029April 28Saturday

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