The older you get, the less you sleep. That’s an overgeneralization, but it is certainly true from birth to age 25 and – unfortunately, elderly people tend to sleep shallower and less than young adults in the same circumstances.
Newborns sleep 16 to 18 hours a day. Half of this is REM sleep and half is slow-wave sleep, with little shallow stage 1 and 2 sleep. By the age of one, children usually sleep 13 to 14 hours with that number decreasing until they reach adolescence. Toddlers typically take afternoon naps prescribed by parents seeking to prevent overtiredness, and the ending of daily naps is seen as a hallmark of maturation for the young child.
As the child grows, time spent in REM declines until it reaches about 90 minutes per night in the mid-teens. Stage 2 sleep increases. Children typically spent a lot of time in slow-wave (Stage 3) sleep which is important for growth. This is why it is so hard to wake kids up during the night. It is hard to awaken anyone from slow-wave sleep but kids spend more of the night in that stage than adults do.
Teenagers generally require at least eight and a half hours of sleep a day. Some experts go so far as to say that teens need more than nine and a half hours each day. With the pressures of academics, athletics, dating, etc., few teens are getting enough sleep these days. Also, teens’ internal biological clocks tend to keep them awake later in the evening and let them sleep later in the morning than adults. They are natural night owls. Some high schools have found that ringing the first bell an hour or so later helps the performance of students. More on adolescent sleep needs.
Young adults (late teens, early 20s) have the lowest rate of sleep disturbances of any age group with the possible exception of babies. They are past the common childhood disorders (night terrors, sleepwalking) but do not yet suffer the insomnia of middle age or the fragmented sleep of old age. This is a generalization, of course, but we can say that young adulthood is the golden age of sleep.
By the mid-20s the shift in circadian cycle in the teenage years has subsided. Some people are owls and some are larks, but the adult distribution of chronotypes is established. Most adults need around eight hours of sleep to function well. The government’s Healthy People 2020 initiative uses a goal of 7 hours per night for adults. (For adolescents the goal is 8 hours per night on school nights.) Although many people claim they require less, only 10% require significantly more or less sleep.
Studies of population groups by socioeconomic status, sex, race/ethnicity, marital status, etc. continue to show age is the biggest demographic factor when it comes to sleep disorders.
For adult women, pregnancy and menopause can cause significant changes in sleep patterns. In the first three months of pregnancy, most mothers-to-be require significantly more sleep than usual and insomnia becomes a problem because of hormone changes. Later in the pregnancy snoring and restless legs syndrome can occur, although these phenomena disappear after the baby is born. Hormonal changes may play a part in why sleep quality declines during menopause. Insomnia, snoring and sleep apnea become more common during these years, perhaps due to the psychological factors associated with menopause or perhaps caused by the aging process and weight gain associated with menopause.
Contrary to the popular belief, the need for sleep does not decline with old age. While the elderly do find that their slumber becomes more fitful, they continue to need about the same amount of sleep that they needed in early adulthood. Experts say that the number of nocturnal awakenings can start to increase as early as the age of 40. Older people more often nap during the day to make up for the lost sleep from the fragmentation at night and because retired people have the opportunity to nap more than working people do. More on insomnia in older people.
Cornell University researchers did a longitudinal study – they followed people for years – and found – no surprise – that people slept shorter times as they got older. The scientists also calculated that both the homeostatic process for sleep regulation and the circadian process declined over time and that the homeostatic process started to decline before the circadian one did.
Jokes abound about lazy teens who seem to sleep all morning and their grandparents who rise before dawn and are in bed in early evening. The stereotypes have grounding in reality, though and are based in biology. It’s not just lifestyle choices of different demographic groups. Scientists have found that the expression of at least some genes associated with the circadian cycle change with age. A paper published in 2015 in the prestigious Proceedings of the National Academy of Sciences announced the finding of a clock mechanism that starts ticking only in the brains of older people.
Scientists found 235 genes that control circadian ryhms in the prefrontal cortex When a person reaches old age, some of these genes essentially shift off – or into low gear where they stop expressing actively. But other genes start expressing and form a new circadian clock – one that is shifted so the individual is more active earlier in the day.
Poor people sleep worse than rich people (weak correlation) and women sleep worse than men, but the transitions from young adult to middle age and from middle age to old age are the biggest inflection points from a public health perspective.