This is the second in a series of columns about the importance of adequate sleep for optimal physical and mental health. These columns are based on the book “Why We Sleep,” by PhD sleep scientist Matthew Walker.

Both length of sleep and quality are important. Adults should get seven (eight ideal) to nine hours of good sleep every night. Typically, humans have four to six sleep cycles a night, each cycle consisting of combinations of NREM (non-rapid eye movement) and REM (rapid eye movement) sleep. NREM sleep is further broken down into 3 sages, with stage 3 called slow wave, deep sleep.

Today’s column is about sleep at different ages. Before reading further, it’s important to know that REM sleep is important in building the trillions of neuro-connections that adult human brains end up with. whereas deep NREM sleep is important getting rid of superfluous connections—a process called pruning.

In utero: Based on sophisticated brain wave and imaging studies, the human fetus spends most of its time in the first and second trimester in a sleep-like state resembling REM sleep. In the third trimester the fetus spends about six hours in NREM sleep, six hours in REM sleep, and twelve hours in an “intermediary sleep state that we cannot confidently say is REM or NREM sleep, but certainly is not full wakefulness.” Alcohol is a strong suppressor of REM sleep and crosses the placental barrier; it also ends up in breast milk. Therefore, for proper fetal and newborn brain development, pregnant and nursing mothers should avoid all alcohol.

Childhood: Infants and young children “display polyphasic sleep:  many short snippets of sleep through the day and night, punctuated by numerous awakenings, often vocal.” This is often detrimental to their parents’ sleep, but fortunately at 3-4 months babies gradually begin to adopt the sleep-wakefulness cycle of their parents. The proportion of REM sleep decreases in early childhood, so a six-month-old infant is 50/50 NREM and REM; a five-year-old is 70/30, and teenagers 80/20.

Adolescence:  The rise in deep, stage 3 NREM sleep peaks just before puberty. At that point, “pruning” of connections becomes top priority. Parents of adolescents need to understand that brain maturation in adolescence proceeds from back to front, so that “the very last stop on the maturational journey…is the tip of the frontal lobe, which enables rational thinking and critical decision-making.” Also of interest is that adolescent teenagers are on a different circadian rhythm than younger children and adults. Their brains aren’t ready for sleep until late in the evening, and aren’t ready to waken until later in the morning. Unfortunately, schools and the rest of society fail to recognize this–to the detriment of teenagers’ mental and physical wellbeing.

Midlife: Young and middle-aged adults regain “normal” circadian rhythms. NREM sleep starts to diminish by late twenties and early thirties, resulting in fewer hours of deep sleep. In the forties, deep NREM brainwaves “become smaller, less powerful, and fewer in number.” By mid and late forties “age will have stripped you of sixty to seventy percent of the deep sleep you were enjoying as a young teenager.”

Old age:  There is a myth that elderly people don’t need as much sleep as younger people, but it isn’t true. As Dr. Walker puts it, [inadequate] “sleep is one of the most under-appreciated factors contributing to cognitive and medical ill health in the elderly.”  By the time people reach seventy, they have lost 80-90 percent of youthful deep sleep. In addition, elderly people experience sleep fragmentation, manifested by waking up throughout the night—due to factors such as aches and pains, weakened bladders, and sometimes side effects from medications. Furthermore, release of the “sleep hormone” melatonin decreases in the elderly. To make matters worse, circadian rhythms change in seniors, with earlier onset of sleepiness (resulting in falling asleep watching TV, making sleeping at night more difficult), and early morning awakening.

If you are elderly and reading this, don’t despair. Strategies for people of all ages to improve quantity and quality of sleep will be discussed in an upcoming column. 

Dr. Greg Feinsinger is a retired family physician who started the non-profit Center For Prevention and Treatment of Disease Through Nutrition. For questions or to schedule a free consultation about nutrition or heart attack prevention contact him at gfeinsinger@comcast.net or 970-379-5718.