Our forefathers broadly divided the 24 hours that go to make a day into three equal portions of 8 hours, one each for work, recreation and sleep. While this was easy arithmetic or a rule of thumb, it turned out to be very scientific as and when data started appearing on the hours of sleep that we need. While the length of sleep required depends on the age and other factors, we are now looking at an average adult doing average type of work, for whom the most optimum length is 8 hours. Let’s see how and why.
When we sleep, our brain doesn’t get switched off completely. It is undergoing cyclical activity which is important for recharging our battery as it were, so that when we get up in the morning, we are fully refreshed and ready to face the world. Our sleep is divided into cycles of brain activity. Each cycle is of roughly 90-110 minutes and we go through five such cycles for a proper, complete sleep, which makes it a total of about 8 hours. The first four cycles are called non-rapid dye movement (NREM) sleep and the last one is called rapid eye movement (REM) sleep in which our eyes keep moving rapidly, hence the name . Both REM and NREM sleeps are vital for fully recharging your battery (http://healthysleep.med.harvard.edu accessed 19 November 2018).
If you don’t sleep long enough for the full five cycles to be completed, you incur what is called ‘sleep debt’, which must be repaid within a few days. If you keep carrying forward your sleep debt, you run into personality problems and poor quality of brain function, including mood swings, anxiety, depression, poor judgment, and so on.
Sleep quality also gets disturbed by things like alcohol, nicotine, dinner time, the type of food you eat and so on. For good sleep, not only should it be near about 8 hours, but it should also be of “normal” timing – you can’t go to sleep at 12 noon and wake up at 8 pm to claim 8 hours. There is a lot of biochemistry and neuroscience involved in this innocuous looking thing called sleep and sleep management is fast becoming a major discipline by itself.