Circadian Clock

Each one of us has a “master clock” inside our brain, known as the suprachiasmatic nuclei (SCN). Its job is to harmonize our biological rhythm with the world that is outside ourselves and entrain us to match our biology to the 24 hour light-dark cycle of the earth. This clock makes it easy for us to get sleepy at nighttime and wake up in the morning. There are many things that control our rhythms, but light is the strongest by far.

Melatonin, which is produced by a small gland in the brain known as the pineal gland, also regulates the sleep and wake rhythm by lowering your body temperature and making you drowsy. Melatonin production and inhibition is controlled by light; blue light (460 nm) especially inhibits melatonin.

If you want to feel the force of your biological rhythm, travel overseas. Jet lag happens when your clock is out of sync with the outside world. That is why you get sleepy in the middle of the day when you are in standing infront of the Eiffel Tower in Paris, only to be wide awake at 3 am.

We are healthiest when we match our daily habits (eating, sleeping, waking) with our biological clock. We function best when we respect that force of nature. Many of our bodily functions rely on a dependable biological rhythm. Very important is the timing of hormonal release such as Growth Hormone, which is secreted during the night. Other examples include thyroid hormone.

Circadian rhythm disorders occur because of disruption in the circadian rhythm. Examples include:

–      Shift work sleep disorder

–      Jet lag

–      Delayed sleep-phase syndrome (“night owl”)

–      Advanced sleep-phase syndrome (“larks”)

–      Blind individuals

Recommendations for improving your circadian rhythm:

– Keep a routine bed and wake time.

– Keep your meals regular.


– Melatonin shifts your circadian rhythm. So if you take it in the evening, you get drowsy earlier. You can take 2 mg melatonin a couple of hours before bedtime.

– Light (sunlight or artificial) is a powerful way to rest your biological rhythm. Early Morning light is especially important. It can help you sleep a bid earlier- about 16 hours after waking up.

– Avoid excessive light exposure during the night to allow your biological rhythm to kick in and get you sleepy. Avoid the use electronics such as laptops and computer screens too close to bedtime (perhaps stop at least 2 hours before).