read Circadian Rhythm: Your 24-hour Body Clock

Circadian Rhythm: Your 24-hour Body Clock

Circadian Rhythm: Your 24-hour Body Clock

You wake up to an alarm at 6am every day for work. But even on a holiday, when there is no alarm, you wake up at the same time. While you may find it a tad inconvenient sometimes, it’s your circadian rhythm or internal body clock at work. 

What is circadian rhythm?

Circadian, derived from Latin, means “around the day”. The circadian rhythm is the 24-hour internal or biological clock that regulates physiological processes such as:  

  • Sleep-wake cycle
  • Body temperature 
  • Hormone activity
  • Blood pressure 
  • Appetite and digestion

It is the master clock that syncs all other biological clocks. The regulator for this clock is located in the brain, in a structure called the suprachiasmatic nucleus (SCN). The SCN comprises about 20,000 neurons (nerve cells), which work in tandem to respond to various environmental cues like the sun’s rays, changes in temperature, and so on. In fact, each cell in the body has its own circadian rhythm, which is ultimately controlled by the master clock in the SCN.

How does it work?

Naturally, the body responds to changes in environmental factors. These responses are regulated by genes, which are unique to each species on earth. 

When there is low light in your surroundings, the cells in your eyes capture the changes and send signals to SCN in the brain. Depending on the intensity of light, the SCN instructs the pineal gland in the brain to increase or decrease the release of the hormone, melatonin. An increase in melatonin at night helps you fall asleep. At sunrise when there is light, your melatonin level drops, which helps you wake up. 

These changes in levels of melatonin activate or deactivate all other circadian rhythms like the release of hormones, including insulin and steroids, which are required for procreation as well as muscle strength (like it is used in hunting a prey). 

Similarly, the body temperature rises and falls in the morning and evening. It remains high during the day, which helps you stay energetic and physically active. At night, it drops to help preserve energy and slow down the body for rest and repair. 

The release of almost all hormones including reproductive hormones, digestive enzymes, activation of hunger and satiety centers, regulation of meal timings, and metabolic activities are inherently tied to the body clock. 

Factors that can disrupt the circadian rhythm

Circadian rhythms are controlled by species-specific genes, but they can be altered by external factors like changes in the amount of natural light reaching the SCN or drugs affecting the release of melatonin. It may be noted that artificial changes in these rhythms can have an adverse effect on health, metabolism, and immunity.

Light: Artificial light from bulbs, LEDs, mobile, computer, and TV screens interferes with the natural working of the circadian rhythm. If you are using these devices till late at night, your brain may think that it is still daytime. This is a major reason behind sleep disorders. Over a period of time, the sleep-wake cycle may adjust to this pattern. However, several other biological clocks may become erratic and never reset.  

Traveling in different time zones: When you fly across different time zones in a short span of time, you experience jet lag. It usually takes about one day per time zone crossed for the brain to adjust to the new time zone. Traveling from west to east causes more problems than traveling from east to west, because the body clock has to be advanced in eastward travel. Thus, it takes slightly longer to adjust to the destination time zone.

Working in shifts: Physiological changes similar to those seen in jet lag are observed in individuals working in shift routines or night duties.  

Medications: Drugs that contain melatonin or caffeine alter the natural rhythm of the body. Sometimes, sleep-inducing or wake-promoting agents have an adverse effect on the circadian rhythm.

Stress: When you are stressed, your body produces a hormone called cortisol, which is also involved in the regulation of circadian rhythm. Overproduction of this hormone may alter the natural rhythm.

Unhealthy lifestyle: Irregular eating habits, consumption of alcohol, extra screen time, etc may disturb your sleep and disrupt the circadian rhythm.

Disruption of circadian rhythm may cause

Sleep disorders: Delayed sleep phase disorder — you may stay awake for two hours or more after normal bedtime
Advanced sleep phase disorder — you may fall asleep earlier than normal bedtime
Insomnia or sleep loss — you may find it extremely difficult to fall or stay asleep

Difficulty in waking up: Those two minutes will never end if you do not fix your sleep cycle

Tiredness: If your sleep routine is disturbed, you may feel tired throughout the day

Hormonal imbalances: Menstrual disturbances and infertility due to disturbances in levels and actions of reproductive hormones

Metabolic disorders: Obesity, diabetes, and other metabolic disorders have been linked to disruption of circadian rhythms

Depression and stress: Disrupted circadian rhythm may cause depression, anxiety, and other mood disorders

Damage to organs, cardiovascular system, metabolism, gastrointestinal system, and skin: This happens over a period of time. It also makes one susceptible to diabetes, obesity, and mental health conditions. Circadian rhythm disorders may also lead to memory loss and delayed healing.

How to have a healthy circadian rhythm? 

Fix a routine: It’s important to have a proper sleep-wake routine. Take the help of an alarm clock if you want to reset your internal clock. After a few days, it will adjust itself to the new schedule. 

Be in the outdoors during the day to promote wakefulness: A stroll in the park or a brisk walk will instantly rejuvenate you and alleviate your senses. Studies have shown that walking outside for 20 minutes enhances vitality and boosts the energy of adults as compared to doing the same indoors. 

Exercise: A good 20+ minutes of cardio, at the start or end of your day, releases endorphins, the happy hormones. It also aids in keeping anxious thoughts away. However, exercising close to bedtime disrupts your sleep cycle due to the release of hormones and endorphins in the body, so it is best to avoid exercising too close to bedtime. 

Sleep well: Optimum room temperature, proper lighting, and a comfortable mattress will help you get a good night’s sleep.    

Avoid caffeine, alcohol, nicotine: Since their effect lasts for five to six hours, you need to control your consumption of caffeine before bedtime. If you want to go to bed at 10pm, then have the last cup of caffeinated drink before 4pm. Alcohol and nicotine should be avoided completely.

Reduce screen time: Blue light coming from your mobile phone, laptop, or TV screen reduces melatonin production by giving it false feedback of day, and may disrupt the circadian rhythm.

Read before bedtime: Reading may help calm your breathing and relax your muscles. Studies have shown that 38% of people who read before bedtime show better sleep quality than those who do not. 

No afternoon or evening naps: Avoid these as they disturb your circadian rhythm, costing you a good night’s sleep.

Circadian rhythm is one of the vital rhythms of the body. Disrupting it may cause a series of health problems. To keep it working smoothly, adopt a healthy lifestyle, get adequate physical activity, rest, and a regular sleep schedule. 

1. Sleep Disorders: Circadian Rhythm Disorder. WebMD. (accessed Jan 28, 2021).
2. Circadian Rhythm Sleep Disorders. Cleveland Clinic. (accessed Jan 28, 2021).
3. Suni E. Circadian Rhythm. Sleep Foundation. (accessed Jan 28, 2021).
4. Silver N. Everything to Know About Your Circadian Rhythm. Healthline. 2020; published online Jul 13. (accessed Jan 28, 2021).
5. Circadian Rhythms. National Institute of General Medical Sciences. (accessed Jan 28, 2021).
6. Waterhouse J. Jet-lag and shift work: (1). Circadian rhythms. J R Soc Med 1999; 92: 398–401.
7. Delezie J, Challet E. Interactions between metabolism and circadian clocks: reciprocal disturbances. Ann N Y Acad Sci 2011; 1243: 30–46.
8. Mills J, Kuohung W. Impact of circadian rhythms on female reproduction and infertility treatment success. Curr Opin Endocrinol Diabetes Obes Dec; 26: 317–21.