Circadian Rhythm

Digital CameraAlhamdulillah, I have a six month old daughter, and every day is full of witnessing wonders of Allah (swt). One thing, which always amazed me, is that healthy babies get up in the early hours of the morning, around Fajr time. This observation sent me to the computer for searching on the Internet about ‘body clocks.’ As I was doing that, I discovered more wonders of Allah’s (swt) creations.

Circadian Rhythm

All living beings have body clocks including humans, plants, animals, fungi and cyanobacteria. This body clock is a 24-hour, 11-minute cycle that exists in the physiological processes of all living things. These cycles became known as ‘circadian rhythm.’ It comes from the Latin word Circa (around) and Dies (day), literally meaning ‘about a day.’ These rhythms are generated within the body, although they can be modulated by external cues, such as light and temperature.

Circadian clocks sense light through a process that transfers energy from light to chemical reactions in cells. These clocks in cells respond to differences in light between night and day and thereby allow organisms to anticipate changes in the environment by pacing their metabolism to this daily cycle.

Circadian Rhythm in Plants and Animals

In plants, the circadian rhythm controls processes, including leaf and petal movements, the opening and closing of stomatal pores, the discharge of floral fragrances and many metabolic activities.

The sleeping and feeding patterns of all animals and their patterns of brain wave activity, hormone production, digestion, cell regeneration and other biological activities are linked to this daily cycle.

Human Body’s Pacemaker

In humans, the circadian clock serves as a pacemaker and is located deep within the brain, where it helps the body keep time. This is the ‘master clock’ of the human body. It controls a number of body functions and interacts with the mechanisms controlling sleep. Recent studies have revealed that organs outside the brain, such as liver, lungs, spleen, etc., have their own rhythm and work independently.

Research has revealed that the circadian clock is affected by light. Darkness stimulates sleep and sunrise triggers the chemical process that enables a person to begin waking up. In the evening, the pineal gland in the base of our brain begins producing the hormone melatonin, which makes us feel sleepy. For most people, studies show that the pressure to sleep builds up throughout the day and peaks around 9 -10 pm. At this time, the body’s temperature starts to drop and lowers about one degree during sleep. As it starts to rise around 4 am, the likelihood of waking increases, and this increase in temperature revives our metabolism for the day ahead.

At dawn, our blood pressure has its sharpest rise, allowing us to assume a vertical position safely. Around lunchtime, our liver enzymes kick into full gear in anticipation of food.

Human body clock also has a built-in alarm system, which is why we often wake up, before our alarm goes off. Researchers conclude that hormones increase because of our anticipation, which is widely thought to be a characteristic unique to conscious action. This pervades sleep and facilitates spontaneous waking. It has also been found that older people rise earlier than young ones.

Out of Sync

Experiments by researchers have revealed that our constant exposure to artificial light is leaving our bodies out of sync with the light rhythms of the natural world. In modern society, we are regularly exposed to artificial light, both in the work place and after the sunset. This extended exposure to artificial light late into the night, along with the shielding from sunlight by curtains and shades early in the morning, could be wreaking havoc with our natural biological clocks.


Disruption of rhythms usually has a negative effect in the short term. Many travelers experience the condition known as jet lag, with its associated symptoms of fatigue, disorientation and insomnia.

Disruption of rhythms in the long term is believed to have significant adverse health consequences on peripheral organs outside the brain, particularly in the development or exacerbation of cardiovascular diseases.

Sunnah of Prophet Muhammad (sa)

Rasoolullah (sa) used to sleep immediately after the Isha prayer, which must have been around 10 pm in Arabia, and he would wake up for Tahajjud, i.e., before Fajr prayer. May be he used to wake up around 4 am, which according to research is the natural circadian time to wake up. However, one constant Sunnah of the Prophet (sa) is that he used to take a short nap in the afternoon for 30 to 45 minutes. This is another thing that researchers are finding very helpful in increasing effectiveness and productivity of a person. In fact, they call it ‘power nap.’


Allah (swt) says in Surah Fussilat (41:53): “We will show them Our Signs in the universe, and in their own selves, until it becomes manifest to them that this (the Quran) is the truth.”

The circadian clock is a sign of Allah (swt) in our own selves. It is an example of His mercy, organisation, tender love, supreme power over mankind and all His living creations. Moreover, the waking and sleeping pattern of Rasool Allah (sa) shows, how close he was to nature and natural laws, Subhan’Allah.