CHAPTER 2

Why Do We Need Sleep?

When we wake from a good night's sleep, we feel physically refreshed But recharging our batteries for the day to come is only one of sleep's functions. Research shows that the purposes of sleep include maintaining key areas of the brain and restoring order throughout the body. Important memory upkeep takes place as we slumber, as well as key metabolic, hormonal and cell repair activity. People who are chronically deprived of sleep are at risk for many health problems, memory failure and accidents resulting from exhaustion.

PART 1 The Brain Needs Sleep

Without adequate sleep, our motor skills and coordination deteriorate. Clumsiness, grogginess and slow reaction times can lead to injuries from accidents or falls. Sleep loss also affects memory recall and performance of math calculations. READ MORE

Sleep has a vital role in helping us process and store memories. During the first half of a full night's sleep, the brain's hippocampus consolidates and stores memories such as factual information, personal memories, autobiographical events and other event- and language-based memories. During the second half of a night's sleep, memories such as new motor skills or habits are consolidated and stored in the brain. LESS

PART 2 The Body Needs Sleep

Many physiological processes slow down during sleep. Your body temperature drops. Your heart rate lowers, and your breathing slows. Your digestive system puts on the brakes. You don't need to run at full throttle, because you are not expending energy on movement. But your body does have some busy night-shift workers. Your immune cells, many hormones, cell repair processes and specific areas of the brain kick into high gear while you are asleep. They tidy up, make repairs and generally prepare your body to thrive during your waking hours. READ MORE

During deep sleep, the phase that scientists call N3 or slow-wave sleep, a burst of growth hormone is released. In growing children and teens, the increase in blood levels of growth hormone is most dramatic. Growth hormone works in tandem with various proteins and specialized growth factors to patch up damaged muscle, skin and bone cells, and to promote the growth of new cells.

Hormones that regulate your appetite are also released during sleep. Leptin is a hormone that tells your brain you are full. Ghrelin is a hormone produced in the stomach that sends signals of hunger. When your sleep is disrupted, the balance of these hormones is disrupted, too.

When you are coming down with a cold or flu, sleep is irresistible. It's as if your body knows it should shut down the main systems and focus on getting well. When you sleep, your bone marrow manufactures many of the immune cells that are your body's natural fighters against illness. Subjects in sleep deprivation studies had lower levels of certain immune cells after missing just one night of sleep. LESS

PART 3 The Ravages of Insomnia

No people are known to have died from sleep deprivation, but animal studies show that sleep deprivation can be deadly. While rats normally live for two to three years, those deprived of REM sleep survived only about 5 weeks. The animals completely deprived of sleep lived only about 3 weeks. READ MORE

Sleep-loss is associated with obesity, inefficient uptake of glucose to use as energy, memory loss and depression. Going without sleep for more than one night can cause hallucinations and mood swings. One theory is that neurons become so overworked that they begin to malfunction. These brain and motor-skill effects cause hundreds of thousands of accidents each year. In sleep-deprivation studies that tested subjects' driving skills, sleep-deprived people performed as badly as, or worse than, people who were drunk. LESS