Around 30 to 50 percent of people sleep between the hours of 11 pm and 7 am. Another 40 percents are either slightly morning people or slightly evening people.
To understand why some people are early birds while others are night owls, we have to take into consideration the body's circadian system.
The body is an orchestra of organs, each providing an essential function. In this metaphor, the circadian rhythm is the conductor. The conductor makes every neurotransmitter, every hormone, and every chemical in the body cycle with the daily rhythm.
This makes us our sleep habits unique and tailored.
It has been associated with higher blood pressure, body mass index, and increased calcification of the coronary artery.