We’re reminded that humans are part of Nature when we discover the many similarities between all living things. One interesting commonality has to do with our circadian rhythms. Circadian rhythms are physical, mental, and behavioral changes that follow a 24-hour cycle. These natural processes respond primarily to light and dark and affect most living things, including animals, plants, and microbes. One example of a light-related circadian rhythm is sleeping at night and being awake during the day.¹

The study of circadian rhythms is called Chronobiology, from the Greek “chronos” meaning time, and “biology” which pertains to the study of science and life. The body follows an internal timekeeping system known as the circadian clock, and this clock is what regulates the natural circadian rhythm.

What makes up the circadian rhythm? Our daily cycles of sleeping and waking, hunger and digestion, hormonal changes and other bodily processes all pertain to the circadian rhythm. Circadian comes from Latin, “circo diem,” which literally translates to “about a day.” Most circadian rhythms automatically reset every in 24 hours, the timeframe for “circo diem.”

Circadian rhythms are not only affected by light and dark, but also by interactions with people, meal times, and hormonal fluctuations. For example, when the sun rises in the morning, the body produces cortisol, a hormone that makes us feel refreshed and alert. After waking, a healthy person will become increasingly tired throughout the day until the sun goes down, when feelings of tiredness are at their highest. As the sun begins to set, the pineal gland will release melatonin, a hormone that reduces wakefulness and alertness.

There are variations on when people feel tired and when they feel alert throughout the day. Two examples are “early risers,” who go to bed and wake up early, and “night owls” who go to bed relatively late and then sleep in. Our sleep rhythm may evolve and change with age—older people tend to go to sleep and wake up earlier in the day than younger people, while babies will sleep in multiple phases throughout the day and night.

A master clock in the brain coordinates all the biological clocks in a living thing, keeping the clocks in sync. In vertebrate animals, including humans, the master clock is a group of about 20,000 nerve cells (called neurons) located in a part of the brain called the hypothalamus where it receives direct input from the eyes. In the grand scheme of Nature, researchers have identified similarities in the master clocks of people, fruit flies, mice, plants, fungi and other organisms!

When our circadian rhythm goes out of whack, it can cause insomnia, weight gain, mood changes, anxiety, shortened attention spans, daytime sleepiness and lethargy. The good news is that we can help keep our circadian rhythm functioning smoothly.

• Wake up every day at the same time: Keeping a regular sleep schedule will help reset your circadian rhythm. Even if unable to fall asleep at the desired time, make sure to set an alarm and wake up at the set time anyway. This will keep you on track.
• Bright light therapy: Exposure to bright artificial lights can re-orient circadian rhythms. Different light therapy devices are available, including lightboxes, desk lamps and sunrise simulators. Before using one of these devices, it’s best to speak with a credentialed sleep medicine physician about the light exposure level and times of the day that are best suited to the particular timing of your personal circadian rhythm.²
• Different meal times: Circadian rhythms regulate when we feel hungry and how we digest food—some studies have found that eating sooner or delaying meals can alter how your circadian rhythm adjusts those processes.
• Exercise: Proper exercise can improve sleep quality and duration, while a healthy sleep-wake cycle ensures more strength and endurance when you work out. However, exercise is also stimulating if you work out too close to bedtime. If you find you don’t get enough sleep at night and want to reorient your circadian rhythm, try incorporating regular exercise into your routine. But as with all things related to the circadian rhythm, timing is important so do not exercise within 1-2 hours of your bedtime.
• Keep your electronic devices off or out of sight. Light from electronic devices at night can confuse our biological clocks.

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1 https://www.nigms.nih.gov/education/fact-sheets/Pages/Circadian-Rhythms.

2  https://www.sleepfoundation.org/circadian-rhythm/can-you-change-your-circadian-rhythm