Circadian Rhythm is your body clock that maintains your day-night rhythm. It is this clock that tells your body when it is time to rest and when its time to be alert and active. Typically this rhythm is maintained by the hypothalamus. The hypothalamus mainly regulates this clock by receiving inputs from the environment- like light, physical and social activities. When it is dark, the pineal gland in your brain secretes melatonin-which sends a signal to your brain and body to get ready for sleep. Light has the opposite effect on the brain.
Historically the sun was our primary source of light, and humans like many other animal species regulated their body clock based on sunlight, and the absence thereof. We have come a long way from those times. Now light from many different sources regulates and sometimes interferes with this rhythm including indoor lights, televisions, cell phones and tablets.
Circadian rhythm sleep disorders are problems with sleep that occur when the circadian clock does not function well. This may happen when the external stimuli are in contradiction to the internal body rhythm. Modern day social and work activities often cause this problem, as does travel. When you travel internationally or across time zones, you may have noticed problems with sleep and wakefulness. Again, this is your circadian rhythm at work. Jet lag happens when you travel to a different time zone and your body struggles to keep up with the change in time. You may feel sleepy and tired or be wide-awake at inconvenient times. Similarly people who work evening and night shifts may experience chronic problems with their sleep. Melatonin can help in both these situations by shifting the circadian clock.
Some people are ‘night owls’, which means they have a different circadian rhythm than most and typically function best and get the most restful sleep when they stay up late and sleep until late in the day. Similarly some people are ‘early larks’ and like to go to get early and are up at the crack of dawn. If you are one of these, you probably already know!
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