A good night's sleep allows us to wake up refreshed, alert and ready to take on our daily activities. Sleep affects how we look, how we feel, and how we perform. Sleep can have a major impact on our quality of life. Both the quantity and the quality of sleep are important to how we feel. Sleep is necessary for muscle repair, memory consolidation, and the release of hormones that regulate growth and appetite. If we do not get enough sleep, our bodies do not have time to complete all these necessary processes.

There is no set number of hours of sleep that people need. Just like many other characteristics, the amount of sleep a person needs is very individual. Some people are at their best with 7 hours of sleep per night while others need 9 hours. Much is being learned about people's basal sleep needs. Studies suggest that most adults need between 7 and 8 hours of sleep per night. Complicating this picture is the concept of sleep debt, which is accumulated lost sleep. For example if you sleep 7 hours on 3 nights of the week but only 6 hours on the other 4 nights, you have accumulated a sleep debt of 4 hours, which may contribute to feeling tired or sleepy on all 7 days of the week. Before the invention of the light bulb, people slept an average of 10 hours a night. Today Americans average 6.9 hours of sleep on weeknights and 7.5 hours on weekends. A lack of sleep can not only reduce productivity and memory and cognition, it can lead to serious health consequences such as increased risk of motor vehicle accidents, appetite stimulation which can lead to obesity, increased risk of diabetes and heart disease, and increased risk of psychiatric conditions including depression and drug abuse.

Healthy sleep consists of both non-rapid eye movement (NREM) and rapid eye movement (REM) cycles that repeat themselves about every 90 minutes throughout the night. NREM sleep accounts for about 75% of the night and is divided into 4 stages. Stage 1 is the time between being awake and falling asleep and light sleep, stage 2 is the onset of sleep when you become disengaged from your surroundings, breathing and heart rates become regular, and body temperature drops, stages 3 and 4 are the deepest and most restful, breathing slows, blood pressure drops, blood flow to muscles increases and muscles relax, tissue growth and repair occurs, energy is restored, and hormones are released such as growth hormone (essential for growth and development) and ghrelin and leptin that regulate appetite. REM sleep first occurs about 90 minutes after falling asleep and recurs about every 90 minutes throughout the night, getting longer as the night goes on. REM sleep represents about 25% of a healthy night’s sleep. REM sleep provides energy to the brain and body and supports daytime performance. During REM sleep the brain becomes active and dreams occur, the eyes dart back and forth, and the body becomes immobile and relaxed as the muscles are turned off. Levels of the stress hormone cortisol dip during the night and gradually increase until the morning when it helps promote alertness upon awakening. Sleep allows us to restore our immune systems and plays a major role in appetite regulation through the hormones ghrelin and leptin. When we are sleep-deprived we feel the need to eat more, which contributes to weight gain.

Far from being an unproductive time, the third of the day we spend sleeping plays a very important role in how full, energetic, and productive the other two-thirds of our day will be.

Reference: http://www.sleepfoundation.org/site/c.huIXKjM0IxF/b.2420541/k.9E5A/How_Sleep_Works.htm.

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