SLEEP WHY WE SLEEP

SLEEP

WHY WE SLEEP

As the field of sleep research is still relatively new, scientists have yet to determine exactly why people sleep. However, they do know that humans must sleep and, in fact, people can survive longer without food than without sleep. And people are not alone in this need. All mammals, reptiles and birds sleep.

Scientists have proposed the following theories on why humans require sleep:

• Sleep may be a way of recharging the brain. The brain has a chance to shut down and repair neurons and to exercise important neuronal connections that might otherwise deteriorate due to lack of activity.
• Sleep gives the brain an opportunity to reorganise data to help find a solution to problems, process newly-learned information and organise and archive memories.
• Sleep lowers a person’s metabolic rate and energy consumption.
• The cardiovascular system also gets a break during sleep. Researchers have found that people with normal or high blood pressure experience a 20 to 30% reduction in blood pressure and 10 to 20% reduction in heart rate.
• During sleep, the body has a chance to replace chemicals and repair muscles, other tissues and aging or dead cells.
• In children and teenagers, growth hormones are released during deep sleep.

When a person falls asleep and wakes up is largely determined by his or her circadian rhythm, a day-night cycle of about 24 hours. Circadian rhythms greatly influence the timing, amount and quality of sleep.

For many small mammals such as rodents, sleep has other particular benefits, as it provides the only real opportunity for physical rest, and confines the animal to the thermal insulation of a nest. In these respects, sleep conserves much energy in such mammals, particularly as sleep can also develop into a torpor, whereby the metabolic rate drops significantly for a few hours during the sleep period. On the other hand, humans can usually rest and relax quite adequately during wakefulness, and there is only a modest further energy saving to be gained by sleeping. We do not enter torpor, and the fall in metabolic rate for a human adult sleeping compared to lying resting but awake is only about 5-10%.

A sizeable portion of the workforce are shift workers who work and sleep against their bodies’ natural sleep-wake cycle. While a person’s circadian rhythm cannot be ignored or reprogrammed, the cycle can be altered by the timing of things such as naps, exercise, bedtime, travel to a different time zone and exposure to light. The more stable and consistent the cycle is, the better the person sleeps. Disruption of circadian rhythms has even been found to cause mania in people with bipolar disorder.

The ‘seven deadly sins’ formulated by the medieval monks included Sloth. The Bible in Proverbs 6:9 includes the line: ‘How long will you sleep, O sluggard? When will you arise out of your sleep?’ But a more nuanced understanding of sloth sees it as a disinclination to labour or work. This isn’t the same as the desire for healthy sleep. On the contrary, a person can’t do work without rest periods and no one can operate at top performance without adequate sleep. The puritan work ethic can be adhered to and respect still paid to the sleep needs of healthy humans. It is wrong to see sleep as a shameful activity.

Usually sleepers pass through five stages: 1, 2, 3, 4 and REM (rapid eye movement) sleep. These stages progress cyclically from 1 through REM then begin again. A complete sleep cycle takes an average of 90 to 110 minutes. The first sleep cycles each night have relatively short REM sleeps and long periods of deep sleep but later in the night, REM periods lengthen and deep sleep time decreases. Stage 1 is light sleep where you drift in and out of sleep and can be awakened easily. In this stage, the eyes move slowly and muscle activity slows. During this stage, many people experience sudden muscle contractions preceded by a sensation of falling. In stage 2, eye movement stops and brain waves become slower with