Circadian rhythms are 24-hour cycles that are part of the body’s internal clock, running in the background to carry out essential functions and processes. They provoke physical, psychological, and behavioral changes primarily in response to light or darkness of an organism's environment. Sleeping at night and being awake during the day is an example of a light-related circadian rhythm.
Biological clocks are an organism’s natural timing device, meaning they regulate the timing of bodily processes, including circadian rhythms. A circadian rhythm is an effect of a biological clock, but not all biological clocks are circadian. For example, plants adjust to changing seasons using a biological clock with timing that is distinct from a 24-hour cycle. There is a so-called Master clock located in the brain, that coordinates all biological clocks in an organism and keeps them in sync. In humans, the master clock is made up of about 20,000 neurons (a structure called the suprachiasmatic nucleus or SCN), located in the region of the brain called the hypothalamus where they receive direct input from the eyes.
How Circadian Rhythms are related to sleep?
Circadian rhythms help determine and regulate our sleep patterns through the production of hormones like melatonin and cortisol. Melatonin is a hormone that makes you sleepy, and your body releases more of it at night and suppresses it during the day. On the opposite Cortisol makes you more alert, and your body produces more of it in the morning. The Master clock or SCN receives information about incoming light directly from the optic nerves, which relay information from the eyes to the brain. When there is less light—like at night—the SCN tells the brain to release more melatonin in order to induce sleepiness.
Changing the light-dark cycles can disrupt the body’s biological clocks. Biological clocks that run fast or slow can result in irregular circadian rhythms, which have been linked to various chronic health conditions, such as sleep disorders, obesity, diabetes, depression, and bipolar disorder.
There is ongoing research focused on finding out the effects night-shift work and exposure to light from mobile devices during the night may have on circadian rhythms and sleep-wake cycles.
How jet lag impacts Circadian rhythms?
Jet lag occurs because your body's clock is still synced to your original time zone, instead of to the time zone where you've traveled. For example, if you fly east from California to New York, you “lose” 3 hours. When you wake up at 7:00 a.m. on the east coast, your biological clocks are still running on west coast time, so you feel the way you might feel at 4:00 a.m. The more time zones crossed, the more likely you are to experience jet lag. Your biological clocks will reset, but it often takes a couple of days, until your body adapts to its new environment.
How Circadian Rhythms are studied
Researchers learn about circadian rhythms by studying humans and other organisms with similar biological clock genes, most commonly fruit flies and mice. Those conducting these experiments control the subject’s environment by altering light and dark periods, after which they look for changes in gene activity or other molecular signals.
Understanding what makes biological clocks tick may lead to new treatments for sleep disorders, obesity, mental health disorders, jet lag, along with plenty other health problems. It can also improve ways for individuals to adjust to nighttime shift work. This research helps us understand how biological clocks work and keep time.
The image shows how time-of-day information flows in the fruit fly brain: Clock neurons (stained in blue) communicate with other nerve cells (stained in red), which then signal to additional neurons (stained in green).
What Circadian Rhythms effect besides sleep?
While the regulation of the sleep-wake cycle is one of the most important aspects/ duties of the Circadian Rhythms, they are involved in the regulation of virtually all systems of the body.
New details about the Circadian Rhythms are constantly uncovered, but so far there has been evidence connecting them to metabolism and weight through the regulation of blood sugar and cholesterol levels. They also influence mental health and the risk of developing psychiatric illnesses and disorders like depression and bipolar disorder; as well as the risk of neurodegenerative diseases like dementia.
Although there is still no hard evidence, there are certain indications that Circadian Rhythms have an effect on the immune system and the processes of DNA repair, which opens up the possibility of its use in cancer prevention.
Mammalian Circadian research timeline
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