The third pillar of health is keeping our circadian rhythm in sync with the day and night cycle of nature. The word circadian comes from the Latin phrase “circa diem,”which means “around a day.” Circadian rhythms exist in most living organisms including plants helping them breath in CO2 at day time and oxygen at night.

Two important hormones body releases are Cortisol and Melatonin. Cortisol is released in the morning and it’s level rises with sunrise and stays high till sunset. It is called the getup and go hormone as it promotes activity. Melatonin rises after sunset and stays high throughout the night. It is a hormone that slows us down and prepares for the sleep cycle. These two hormones counteract and determine our circadian rhythm.

HOW DOES CIRCADIAN RHYTHM WORK?
The circadian rhythms throughout the body are connected to a master clock, sometimes referred to as the circadian pacemaker, located in the brain. Specifically, it is found in a part of the brain called Suprachiasmatic Nucleus (SCN) in the hypothalamus. At different times of the day, clock genes in the SCN send signals to regulate activity throughout the body. Various systems of the body synchronize to this master clock. The master clock synchronizes itself to the nature’s clock via multiple mechanisms that we have only recently begun to understand.

The SCN is highly sensitive to light, which serves as an critical external cue that influences the signals sent by the SCN to coordinate internal clocks in the body. For this reason, circadian rhythms are closely connected to day and night. While other cues, like food intake, exercise, social activity, and temperature, can affect the master clock, light is the most powerful influence on circadian rhythms.

There is a protein called Melanopsin, discovered less than 20 years ago, which has a light sensing mechanism and it is present only in about 5,000 neurons of each eye. These neurons are hard wired to the master clock in the brain. Through these cells we perceive daylight and adjust our master clock in the brain.

2017 Nobel laureates Jeffrey C. Hall, Michael Rosbash and Michael W. Young discovered how plants, animals and humans adapt their biological rhythm so that it is synchronized with the Earth’s revolutions. They isolated a gene called Period that controls the normal daily biological rhythm. They showed that this gene encodes a protein called PER, that accumulates in the cell during the night, and is then degraded during the day.

There also is a gene called Timeless which makes a protein called TIM which combines with PER to enter the nucleus of the cell and helps maintain the cycle. The clock regulates various functions like hormone levels, sleep, body temperature, metabolism and even behavior. When we change our lifestyle to bring it in harmony with circadian rhythm, results are remarkable.