The importance of sleep
We normally sleep at night and are awake during the daytime. As a matter of fact, we all know the saying, "early to bed, early to rise makes a man healthy, wealthy and wise," which suggests that most of us function best when this pattern is followed. Is there any truth to this and what would be the basis of it?
The 'master biological clock' is located in a part of the brain called the hypothalamus. This 'clock' controls the circadian rhythms, which according to the National Institute of General Medical Sciences, are "physical, mental and behavioural changes that roughly follow a 24-hour cycle which primarily respond to light and darkness changes in an organism's environment". Light is the main cue that influences our circadian rhythms, but internal processes maintain them without any external influence, even in prolonged darkness. The cycle can be adjusted by changes in light or darkness patterns, such as what occurs when we move from one time zone to another.
The circadian rhythms influence sleep/wake cycles, release of hormones, body temperature and other bodily functions. It does so by switching certain genes on and off at various times. Here are some examples. The release of melatonin, the main hormone responsible for sleep normally occurs from 11 p.m. to 7:30.am. Our deepest sleep is normally at 2 a.m. Our bowel movements are suppressed at night, but are most likely to occur at around 8:30 a.m. Our lowest body temperature occurs at 4:30 a.m. and our highest at 7 p.m. There is a sharp rise in our blood pressure at 6:45 a.m. The highest testosterone secretion occurs at around 9 a.m.
Our circadian rhythms can be disrupted by internal or external factors. When internal factors are at play, there is usually disrupted sleep patterns, such as insomnia. External influences occur when we force ourselves to be awake during times when we should be sleeping, such as what happens during shift work. Disruptions in our circadian rhythms have been linked to the development of diabetes, obesity, cancer, gastrointestinal problems and psychological problems such as depression and bipolar disorder. This probably occurs due to the disruptions that occur to the genetic switches mentioned earlier.
Another very important fact is that our circadian rhythms may vary from one person to the other, so one person's most alert time may differ from another, and may even vary throughout a person's life.