Human sleep consists of 20-25 percent REM (rapid eye movement) and 75-80 percent Non-REM sleep. During REM sleep, the eyes move rapidly and most people experience dreams. This is also called “dream sleep.” REM sleep is important for controlling mental stress and emotion, and memory consolidation. The human brain is active during REM sleep, but a subject cannot move at the time or remember this brain activity in the morning.
Non-REM sleep is classified into three steps: N1 (light sleep), N2 (deeper sleep) and N3 (deepest sleep). N1 sleep is a transition between sleep and waking. So it is not real sleep. N2 sleep is characterized by sleep spindles and K-complexes on an electroencephalogram (a method of recording the electrical activity of the brain). N3 sleep is the deepest, and is needed to recover from fatigue and energy loss during the daytime. Poor-quality sleep means a decrease in N3 sleep and REM sleep and an increase in N1 sleep.
The amount of REM and N3 sleep is the most important factor for the memory and improvement of skills which were learned during the daytime. If a person has enough good-quality sleep, memory and skill will improve over next four-five days. But if he or she is sleep deprived, no improvement of memory and skill occurs. So an adequate amount of sleep is vital for good school performance and work efficiency.
Daily sleep time has greatly decreased over the last 50 years from 8.5 hours in 1950 to 6-7 hours in 2000 because of increased workload and night activities in the modern lifestyle. This lack of sleep has brought about a lot of problems including traffic accidents, the Challenger space shuttle disaster in 1986, the Chernobyl nuclear power plant disaster, poor school and work performance, and an increase in mental and physical diseases.
The necessary amount of daily sleep differs according to age. Young adults need 7.5 hours of sleep per day, adolescents need more than eight hours and elementary school students should sleep more than nine hours. Korea is the worst country in terms of sleep deficiency. The average Korean 12th grader only gets five hours of sleep per day. Most Korean parents push their children into a severely sleep deficient state, which impairs their school performance and mental and physical health. The Korean government has not yet realized the seriousness of chronic sleep deficiency.
Not only the absolute amount, but the quality of sleep is important as well. There are many sleep disorders which interfere with sleep and cause poor-quality sleep. The most frequent cause of poor-quality sleep is obstructive sleep apnea. People with OSA literally stop breathing repeatedly during their sleep, often for a minute or longer and as many as hundreds of times during a single night. N3 and REM sleep are dramatically decreased or nearly absent in most OSA patients. So they are tired and experience a lack of energy, decrease in work efficiency, and decline in concentration and memory.
OSA significantly increases the risk of hypertension, diabetes mellitus, strokes and heart disease. If you don’t treat OSA, your lifespan is reduced. So if your bed partner notices that you have moderate to severe snoring or sleep apnea (you stop breathing during sleep), you should go to a sleep clinic. The most effective treatment for OSA is nasal CPAP (continuous positive airway pressure). CPAP is an airway treatment that uses slight positive pressure during inhalation to increase the volume of inhaled air and decreases the work of breathing. OSA patients should reduce their body weight and stop drinking alcohol and smoking.
Sleep can be disturbed by other sleep disorders such as insomnia (difficulty falling asleep or maintaining sleep), restless leg syndrome (the urge to move or leg discomfort or pain at bedtime), periodic limb movements during sleep (periodic leg jerking during sleep) and parasomnia (sleepwalking, REM sleep behavior disorders, etc.). If you have any problems sleeping at night, or unexplainable daytime sleepiness or fatigue, don’t hesitate to contact a sleep clinic. They may be able to change your life greatly.
By Hong Seung-bong
The author is a doctor at Samsung Medical Center and a professor of neurology at Sungkyunkwan University’s School of Medicine. ― Ed.