How your age affects your sleep

To a certain extent, heredity determines how people sleep throughout their lives. Identical twins, for example, have much more similar sleep patterns than nonidentical twins or other siblings. Differences in sleeping and waking seem to be inborn. There are night owls and early-morning larks, sound sleepers and light ones, people who are perky after five hours of sleep and others who are groggy if they log less than nine hours. Nevertheless, many factors can affect how a person sleeps. Aging is the most important influence on basic sleep rhythms — from age 20 on, it takes longer to fall asleep, you sleep less at night, Stages N1 and N2 sleep increase, Stage N3 sleep and REM sleep decrease, and nighttime awakenings increase.

Childhood

For an adult to sleep like a baby is not only unrealistic but also undesirable. A newborn may sleep eight times a day, accumulating 18 hours of sleep and spending about half of it in REM sleep. The REM to non-REM cycle is shorter, usually lasting less than an hour.

At about the age of 4 weeks, a newborn's sleep periods get longer. By 6 months, infants spend longer and more regular periods in non-REM sleep; most begin sleeping through the night and taking naps in the morning and afternoon. During the preschool years, daytime naps gradually shorten, until by age 6 most children are awake all day and sleep for about 10 hours a night.

Between age 7 and puberty, nocturnal melatonin production is at its lifetime peak, and sleep at this age is deep and restorative. At this age, if a child is sleepy during the day, parents should be concerned.

Adolescence

In contrast, adolescents are noted for their daytime drowsiness. Except for infancy, adolescence is the most rapid period of body growth and development. Although teenagers need about an hour more sleep each day than they did as young children, most of them actually sleep an hour or so less. Parents usually blame teenagers' busy schedule of activities for their grogginess and difficulty awakening in the morning. However, the problem may also be biological. One study indicated that some adolescents might have delayed sleep phase syndrome, where they are not sleepy until well after the usual bedtime and cannot wake at the time required for school, producing conflicts between parents and sleepy teenagers as well as with secondary schools, which usually open earlier than elementary schools. It is unknown whether this phase shift occurs primarily as a physiological event or as a response to abnormal light exposure.

Adulthood

During young adulthood, sleep patterns usually seem stable but in fact are slowly evolving. Between age 20 and age 30, the amount of slow-wave sleep drops by about half, and nighttime awakenings double. By age 40, slow-wave sleep is markedly reduced.

Women's reproductive cycles can greatly influence sleep. During the first trimester of pregnancy, many women are sleepy all the time and may log an extra two hours a night if their schedules permit. As pregnancy continues, hormonal and anatomical changes reduce sleep efficiency so that less of a woman's time in bed is actually spent sleeping. As a result, fatigue increases. The postpartum period usually brings dramatic sleepiness and fatigue — because the mother's ability to sleep efficiently has not returned to normal, because she is at the mercy of her newborn's rapidly cycling shifts between sleeping and waking, and because breast-feeding promotes sleepiness. Researchers are probing whether sleep disturbances during pregnancy may contribute to postpartum depression and compromise the general physical and mental well-being of new mothers.

Women who aren't pregnant may experience monthly shifts in sleep habits. During the second phase of the menstrual cycle, between ovulation and the next menses, some women fall asleep and enter REM sleep more quickly than usual. A few experience extreme sleepiness. Investigators are studying the relationship between such sleep alterations, cyclic changes in body temperature, and levels of the hormone progesterone to see whether these physiologic patterns also correlate with premenstrual mood changes.

Middle age

When men and women enter middle age, slow-wave sleep continues to diminish. Nighttime awakenings become more frequent and last longer. Waking after about three hours of sleep is particularly common. During menopause, many women experience hot flashes that can interrupt sleep and lead to chronic insomnia. Obese people are more prone to nocturnal breathing problems, which often start during middle age. Men and women who are physically fit sleep more soundly as they grow older, compared with their sedentary peers.

The later years

Like younger people, older adults still spend about 20% of sleep time in REM sleep, but other than that, they sleep differently. Slow-wave sleep accounts for less than 5% of sleep time, and in some people it is completely absent. Falling asleep takes longer, and the shallow quality of sleep results in dozens of awakenings during the night. Doctors used to reassure older people that they needed less sleep than younger ones to function well, but sleep experts now know that isn't true. At any age, most adults need seven and a half to eight hours of sleep to function at their best. Since older people often have trouble attaining this much sleep at night, they often supplement nighttime sleep with daytime naps. This can be a successful strategy for accumulating sufficient total sleep over a 24-hour period. However, if you find that you need a nap, it's best to take one midday nap, rather than several brief ones scattered throughout the day and evening.

Sleep disturbances in elderly people, particularly in those who have Alzheimer's disease or other forms of dementia, are very disruptive for caregivers. In one study, 70% of caregivers cited these problems as the decisive factor in seeking nursing home placement for a loved one.

Sleep
Need better sleep? Learn how to get it with Improving Sleep: A Guide to a Good Night's Rest. This special report from Harvard Medical School describes the factors that can disturb sleep, the latest in sleep research, and, most importantly, what you can do to get a good night's sleep. It also includes in-depth information on sleep disorders, including restless legs syndrome, narcolepsy, and sleep apnea.