The Rhythm is Going to Get You
Ever wonder how your body knows when it is time to sleep?
Well, there are two main factors that have powerful influence on your mind and body. The first is literally your internal 24-hour clock, located deep in the brain. This clock creates a regular day-night rhythm that makes you feel tired or alert at regular times of night and day. The second is a chemical substance that builds up in your brain as you are active and creates a need to sleep - I discussed this in my last blog - adenosine the chemical barometer in your body that registers the amount of lapsed time since you woke up.
The clock I refer to is your circadian rhythm. Everybody has one, in fact almost all life on earth has one. The biological name for it is the suprachiasmatic nucleus and is situated behind your eyes in the middle of your brain, slightly above where the two optic nerves from your eyes cross over. There is good reason it sits there, as what it does is 'sample' the light signal being sent from each eye to the brain for visual processing and uses this light information to calibrate itself. It controls a vast array of behaviors including when you want to be awake and asleep. For species like us, that are active during the day, the circadian rhythm activates many brain and body mechanisms during daylight hours that are designed to keep you awake and alert. These processes are ratcheted down at night-time, removing the alerting influences. For example, your body temperature - your body temperature rises as daylight evolves and peaks late in the afternoon. It then begins to decline again reaching it's lowest point about 2 hours after sleep onset. However, it does not require you to be asleep, the rhythm will lower your body temperature irrespective of that, as it is driven by the cyclical rhythm of light and dark.
Interestingly, the circadian rhythm is quite personal. Although it is a common 24 hour pattern (really it's cycle is about 24 hours and 15 minutes) across all humans, for some people, their peak of wakefulness arrives early in the day and their sleepiness trough arrives early at night - so called 'morning larks'. They are about 40% of the population. Others naturally prefer to go to bed late and wake up late - the 'night owls'. They make up about 30% of the population. Your chronotype is strongly determined by genetics. If you are a true 'night owl', society is slightly bent against you as we can see from our school and working schedules. The other 30% are somewhere in between.
Spare a thought also for adolescent teenagers. They have a different circadian rhythm from both younger children and older adults. As they row through puberty their rhythm shifts forward, meaning that their need to sleep becomes later and their need to wake-up also becomes later. For a 16 year old, peak wakefulness is still in operation at 21:00! By the time the parents get tired and want everybody in bed, the teenagers may still be very much awake. The parents then want their teenagers to be awake and up at a 'reasonable' time the following morning, but at this stage, the teenager may still be in the trough of their rhythm. Working against teenagers are their parents and society with school starting times very much against them. As the teenager enters into young adulthood the circadian rhythm slides back to a rhythm more in tune with parental and societal expectations!
Your circadian rhythm is difficult to shift. It is estimated that for every day you are in a different time zone that your circadian rhythm can only adjust by about one hour. For example, San Francisco is about 8 hours behind Dublin and so it would take up to 8 days for the circadian rhythm to fully realign itself with the local day/night ebbs and flows if you move between these 2 cities. Hence jet lag! Your circadian rhythm tells you that you need to be asleep or awake whilst the day/night conditions in your location are demanding otherwise.
I find sleep a fascinating subject and it is just as important for our health - physical and mental - as exercise and diet. If you want to discover more I recommend 'Why We Sleep' by Matthew Walker, a book that clearly and easily provides the science behind our sleep patterns and dreams.
