'Nature's Chief Nourisher'

A newborn sleeps for frequent short periods that total about 18 hours a day. According to sleep specialists, although some adults appear to need only three hours of sleep a day, others
need up to ten hours.

Recent research has shown that variations in our biological dock also explain why some teenagers struggle to get out of bed in the morning. The biological dock seems to shift forward during puberty, making youngsters want to go to sleep later and wake up later. This sleep delay is common and tends to disappear, in the mid-to-late teens.
Our biological dock is regulated by chemical substances, many of which have already been identified. One of them is melatonin, a hormone thought to trigger sleepiness. Melatonin is produced in the brain, and some scientists believe that it is responsible for the slowdown of the body's metabolism that occurs prior to falling asleep. As melatonin is released, body temperature and blood flow to the brain are reduced, and our muscles gradually lose their tone and become flaccid. What happens next as the person descends into the mysterious world of s1eep?

Approximately two hours after we fall asleep, our eyes begin to quiver quickly back and forth. The observation of this phenomenon led scientists to divide sleep into two basic phases: REM (rapid eye movement) sleep and non-REM sleep. Non-REM sleep can be subdivided into four stages of progressively deeper sleep. During a healthy night's sleep, REM sleep occurs several times, alternating with non-REM sleep.
Most dreaming occurs during REM s1eep.
The body also experiences maximum muscle relaxation, which allows the sleeper to wake up feeling physically refreshed. In addition, some researchers believe that newly acquired information is consolidated as part of our long-term memory during this sleep stage.
During deep sleep (non-REM sleep stages 3 and 4), our blood pressure and heart rate reach lower ranges, providing rest for the
circulatory system and helping to ward off cardiovascular disease. In addition, the pro-duction of growth hormone peaks during non-REM sleep, with some teenagers producing as much as 50 times more growth hormone at night than during the day.
Sleep also seems to affect our appetite.
Scientists have discovered that sleep really is, to quote Shakespeare, "chief nourisher in life's feast." Our brain interprets a lack of sleep as a lack of food. While we sleep, our organism se-cretes leptin, the hormone that normally lets our body know that we have eaten enough. When we stay awake longer than we should, our body produces less leptin, and we feel a craving for more carbohydrates. So sleep
deprivation can lead to increased carbohydrate consumption, which in turn can lead to obesity.
Vital for Health
But that is not all. Sleep makes it easier for our body to metabolize free radicals-mole-cules that are said to affect the aging of cells and even cause cancer. In a recent study carried out by the University of Chicago, 11 hea1thy young men were allowed only four hours of sleep a day for six days. At the end of this period, their body cells were performing like those of 60-year-olds, and their blood insulin level was comparable with that of a diabetes sufferer! Sleep deprivation even affects the production of white blood cells and the hormone cortisol, making a person more prone to infections and circulatory diseases.
Without a doubt, sleep is vital for a hea1thy
body and mind. In the opinion of researcher William Dement, founder of the first sleep study center, at Stanford University, U.SA., "sleep seems to be the most important indicator of how long you'll live." Deborah Suchecki, researcher at a sleep study center in Silo Paulo, Brazil, comments: "If people knew what is going on in a sleep-deprived body, they would think twice about conc1uding that sleep is a waste of time or just for the lazy."-See the box above.
But is all sleep restorative? Why do some people sleep the whole night and still feel unrefreshed? The next artic1e will help you identify some of the principal sleep disorders and will explain how you can get quality sleep.