I was wondering. Why is it that I seem to be more tired than I used to be ten years ago yet I’m doing less? I seem to need to go to sleep earlier, cannot seem to fit as much into my day, is it age? Do I need more sleep as I get older? I decided to find out.
Over a typical lifespan, the amount of time we spend each day sleeping declines. Newborns spend from 16 to 20 hours asleep each day. Between the ages of one and four, total daily sleep time decreases to about 11 or 12 hours. This gradual decline continues through childhood, such that an adolescent will need—though not necessarily get—about nine hours of sleep to function at his or her best. Adults through middle age need at least eight hours, and although the elderly may still require up to eight hours, they may struggle to obtain those hours in one block.
In addition to changes in sleep duration, sleep patterns also change as we age. In many cultures, napping continues to be a normal part of daily life for both young and old. This practice, which in Spanish-speaking countries is called a siesta, tends to be more common in the tropics than in more temperate latitudes. Naps in these cultures typically take place in mid-afternoon and coincide with the hottest time of day, as well as a lull in the brain’s alerting signal that works to counteract the drive to sleep.
As a consequence of these regular daytime naps, nighttime sleep is often shifted to a later hour than it is for societies or individuals that don’t nap during the day.
Sleep stage variations
Although it may appear so from the outside, sleep is not a completely inactive state. During sleep, the brain’s activity changes in characteristic ways over the course of the night. These patterns have been classified into two main types of sleep: rapid-eye-movement (REM) sleep and non-rapid-eye-movement (NREM) sleep. NREM sleep is broken down into three distinct stages: N1, N2, and N3. These stages are characterized by increasingly larger and slower brain waves. N1 sleep is very light sleep; N2 is slightly deeper sleep; and N3, also called slow-wave sleep, is the deepest NREM sleep stage.
REM sleep, which is often associated with dreaming, is thought to assist in brain development, especially early in life. Not surprisingly, newborns and infants typically spend about twice as much time as adults in REM sleep. Interestingly, the neurological barrier that inhibits muscles in the legs and arms from contracting during REM sleep and prevents people from “acting out” their dreams is also not fully developed in newborns. Without full inhibition, brain activity associated with REM sleep can result in dramatic twitches and movements of an infant’s limbs. Some of these are strong enough to stir the child from sleep. Only during the second six months of life does the system develop sufficiently to inhibit dramatic body movements during REM sleep.
Sleep cycles, composed of REM and NREM sleep, last for about 50 minutes in children and 90 minutes in adults. Infants’ and children’s cycles contain a relatively large amount of slow-wave (N3) sleep—the non-dreaming, restorative kind that is also known as deep sleep. In early adulthood the amount of slow-wave sleep begins to decline. Elderly adults typically have relatively short periods of slow-wave sleep and fewer of them. In other words, sleep is lighter and more fragmented with brief arousals or longer awakenings throughout the night.
All in the timing
As children pass into adolescence, both the stages of sleep and the sleep cycle remain largely unchanged. One thing that does change, however, is the timing of their sleep. Humans possess an internal 24-hour clock, also called the circadian pacemaker, that partly determines the time when people fall asleep and when they wake, as well as their alertness level while they are awake. Interestingly, due to changes in the circadian alerting system related to development, the preferred times for falling asleep and waking are typically delayed in adolescents. This leads to many high school students going to bed relatively late at night because their internal clock prevents them from feeling sleepy until later. However, school start times are usually much earlier than the typical adolescent’s naturally preferred wake time. As a result, many students must wake at unusually early phases of their internal circadian cycle and after inappropriately short sleep duration. Also, exposure to artificial indoor light in the evening fools the internal clock into thinking it is earlier than it actually is, which can make this problem worse. Many students try to catch up on their sleep by sleeping late on the weekends, but this only shifts their internal clock further out of phase with their weekday schedule.
Because their body rhythms drift in a later direction, many teens struggle to wake up for school.
Another important change with aging results from changes in how the two systems that regulate the timing of sleep—the sleep-wake homeostat and the internal clock—interact with each other. Under normal conditions, these two systems keep us alert throughout the day and enable us to sleep throughout the night. As people age, however, the window during which the internal clock enables sleep narrows. This may explain why older people tend to wake up early in the morning and fall asleep earlier in the evening, and also why they may not be able to nap in the early part of the day.
This article was from the Division of Sleep Medicine, Harvard Medical School