Lark or Owl: How Circadian Rhythms Affect Our Health?

Circadian rhythms are responsible for sleep and wakefulness preferences, food intake, a person’s physical and cognitive abilities, the body’s production of hormones, and even our human temperature.

Circadian rhythms are a person’s biological clock.

What are Circadian Rhythms?

All living organisms on the planet have circadian rhythms. In humans, the main circadian rhythm is the sleep-wake cycle. The central circadian clock that controls our rhythms is located in the suprachiasmatic nucleus of the hypothalamus, which directly receives light and dark stimuli from the retina and correlates them with sleep time preferences.

Having a biological clock allows the body to anticipate predictable changes in the environment and adjust behavior in advance to take these conditions into account. For example, knowing that dawn will come in three hours, the body begins to increase metabolic rate, temperature, increase blood circulation. All of this prepares us for active behavior during the day. In the evening, when we prepare for sleep, physiological processes in the body begin to slow down.

During sleep, the brain is working actively. It records memories, processes information, solves problems, sends signals to repair damaged tissues, and regulates energy stores. Some parts of the brain are more active during sleep than during wakefulness.

Scientific studies have shown that disruption of circadian rhythms can lead to metabolic diseases such as diabetes, obesity, cancer, neurodegenerative diseases, increased risk of mortality from cardiovascular disease and stroke.

During the circadian day (wakefulness), our bodies process nutrients to obtain energy for an active daytime life. During the circadian, tissue repair occurs due to stored nutrients. These changes in metabolic intensity are regulated by the endocrine system, i.e. hormones.

Important hormones in our body are also linked to circadian rhythms.

Melatonin, The Sleep Hormone

  • Naturally produced by the body
  • Comes from certain foods
  • May come from supplements

Melatonin is produced by the body between 23:00 and 1:00 am. This is also the time when all important hormones related to circadian rhythms are synthesized, so it is highly advisable to be in the deep sleep phase at this time.

The importance of this hormone can be seen from its functions in our body:

  • Ensures effective work of the endocrine system
  • Slows down the aging process
  • Promotes adaptation of the organism to the change of time zones
  • Stimulates the protective functions of the body’s immune system
  • Has an antioxidant effect
  • Helps the body fight stress
  • Regulates the cardiovascular system and blood pressure
  • Influences the production of other hormones in the body
  • Participates in the digestive system

As you can see, impaired synthesis of this hormone can affect many processes of your body.

Cortisol - Hormone That Can Be Good or Bad

Most often we hear that cortisol is the stress hormone. We get the impression that we need to “fight” it somehow. Few people know that cortisol initially performs the most important function – anti-stress. But let’s go in order.

Cortisol is a hormone that is synthesized by the adrenal glands. The adrenal glands are paired endocrine glands that secrete more than 50 essential hormones for our body.

If the adrenal glands are working properly, the hormone cortisol acts as a good hormone:

  • Participates in metabolic processes
  • Preserves energy in the body
  • Activates and mobilizes the body’s resources in case of stress

Cortisol starts its work in our body with a surge. Simply put, it wakes us up in the morning and supports the body with several peaks throughout the day. By evening, cortisol’s work decreases.

In order for cortisol to remain the “good guy”, we need to keep its levels in the body at optimal levels. Low or high cortisol levels make it the “bad guy”. Let’s look at the signs that cortisol levels in the body are abnormal.

Signs of Increased Cortisol Levels

  • Can’t fall asleep for a long time
  • You may wake up several times during the night
  • Irritable in the morning
  • You have strong cravings for sweets and salty foods
  • Weight doesn’t go down even when you eat right
  • Fat on your abdomen and flanks
  • You have tremors in your hands

Signs of Low Cortisol Levels

  • Feeling tired, even after a good long sleep
  • You fall asleep “on the go” after a meal.
  • Only coffee or energy drinks help you to wake up

Causes of Impaired Cortisol Levels

  • Stress
  • Low-carb diets
  • Late or exhausting workouts
  • Disruption of circadian rhythms

Long-term Effects of Disrupting Cortisol Levels in the Body

  • Thyroid dysfunction
  • Carbohydrate metabolism disorder
  • Insomnia
  • Depression, chronic fatigue syndrome

Ways to Normalize Cortisol Level

  • A balanced diet, including a good amount of the right carbohydrates
  • A diet rich in Omega-3, vitamin C, B vitamins, 5-HTP
  • Minimize the amount of coffee
  • Sufficient amount of Magnesium in the body
  • Sleep according to circadian rhythms.

Somatotropic Hormone or Growth Hormone


The hormone reaches its highest peak during sleep at night from 23-24 to 1-2, so it is recommended to sleep at this time.

Somatotropin in the body is stimulated by protein foods. The more protein foods in your diet, the higher the growth hormone. Fast carbohydrates and saturated fatty acids – white bread, sweets, pastries and muffins depress somatotropin.

You should also avoid eating simple carbohydrates just before going to bed, as this provokes an increase in blood glucose levels and the release of insulin, which is the main opponent of growth hormone and suppresses it.

Functions of Somatotropic Hormone

  • Normalizes metabolic processes in the body, using proteins as building material for muscles
  • Increases the breakdown of fats
  • Slows catabolism (muscle breakdown)
  • Strengthens bones, ligaments and joints
  • Improves skin condition
  • Improve immune system
  • Accelerates the healing process of wounds


As we can see, the hormones that are responsible for the most important functions in our body work at certain hours. And “owls” who skip these hours, staying awake at night, do not help their body to fulfill its tasks.

Many studies have been conducted in the world, proving that the interruption of circadian rhythms can lead to the development of various diseases.

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