The right mix of sleep

Sleep research shows that adults of every age need, on average, a range of seven to nine hours of sleep each night, teenagers need about 9.5 hours, and infants generally require around 16 hours per day. But just as important as the amount of sleep is getting the right mix of REM and NREM sleep, as well as shallow and deep sleep. In normal sleep, REM and NREM sleep alternate throughout the night according to a predictable pattern referred to as the “sleep architecture".

A complete sleep cycle consists of NREM and REM cycles that alternate every 90 to 110 minutes and is repeated four to six times per night. Adults, on average, spend more than half of their total daily sleep time in stage 2 sleep, about 20 percent in REM sleep, and the remaining time in the other stages, but the amount of time spent in any given stage is not constant over the course of a night. The first sleep cycles each night contain fairly short periods of REM sleep and longer periods of slow wave sleep. As the night wears on, REM periods increase in length while the amount of slow wave sleep decreases. By morning, nearly all sleep is in stages 1, 2, and REM.

In addition to these nightly changes, the sleep architecture also varies over the course of a lifetime. Normal adults spend 20-25 percent of sleep time in REM, which is constant throughout adulthood, but newborn babies spend about half their time in REM sleep. Young children also have substantial amounts of deep NREM sleep, but as people age, the amounts of stages 3 and 4 NREM sleep decrease, with lighter sleep predominating. Although sleep may become more fragile in older people, the need for sleep does not decrease with age.

Although scientists still are trying to find out why people need sleep, research on the sleep of animals shows that sleep is necessary for survival. Some experts believe sleep allows the body to repair itself; during sleep many cells show increased production of proteins, the essential building blocks needed for cell growth and repair of damage from stress and ultraviolet rays. The fact that many biochemical and physiological processes take place during sleep has led to a consensus among researchers that adequate sleep is essential to health and wellness.

A look at the impact of sleep loss on physiological and cognitive functions can also help shed light on the purpose of sleep. Some of these functions include memory and attention, complex thought, motor response, and emotional control. But sleep loss does far more than make us grumpy and groggy. In the past few years, investigators have found that sleep loss may have harmful consequences for our immune and endocrine systems, as well as contribute to serious illnesses such as obesity, diabetes, and hypertension.

Although the role each of these stages plays in overall health is uncertain, having the right balance between them is believed to be important for obtaining restful, restorative sleep and for promoting processes such as learning, memory, mood, and ability to concentrate.