Everyone's sleep pattern changes throughout life: Babies sleep the day away, while seniors often get by on a handful of hours nabbed here and there. Sleep habits also change depending on your age. You might find yourself waking up earlier or staying up later. It may become harder to fall asleep or stay asleep because, as you get older, you're more vulnerable to specific sleep disorders like delayed sleep phase syndrome, insomnia, or sleep apnea.
But no matter what your age or stage, there are two alternating types of sleep to every cycle: non-rapid eye movement (NREM), or quiet sleep, when tissue growth and repair occur; and rapid eye movement (REM) sleep, when the brain is active, memories are consolidated, and dreaming occurs.
"Sleep is basically a critical state," said Christopher Drake, PhD, a sleep researcher at the Henry Ford Sleep Disorders and Research Center and an associate professor of psychiatry and behavioral neurosciences at the Wayne State University School of Medicine in Detroit. "It's critically important to our survival, and our sleep needs change as we grow and age."
Children and Sleep
Children need a lot of sleep. Newborns sleep an average of 16 to 18 hours a day, and toddlers sleep about 12 to 14 hours. By age 2, most children have spent more time asleep than awake. A typical kid will spend 40 percent of his or her childhood asleep. Even 12-year-old adolescents should still be sleeping 10 to 11 hours every day.
Babies may spend as much as half their total sleep in the REM stage and can go directly into REM sleep from wakefulness, unlike older children and adults. However, by age 2, children have the same relative length of REM sleep they will need for the rest of their lives.
"It's most likely due to the fact that their brains are in a developmental stage," said Drake. "They're still growing, and our brain thrives on sleep. When we sleep, we solidify the things we learned during the day. For infants that involves a lot of new material."
Children also spend a great deal of time in NREM, or slow-wave sleep, the very deep sleep in which the body restores itself. Important hormones for growth and development are released during this deep state. Blood supply to the muscles increases, and tissue growth and repair occurs.
Teenagers and Sleep
Teenagers can have a troubled relationship with sleep. They need at least 8½ hours of sleep a night, but physical, emotional and social changes often hamper their ability to get the length of sleep they need. One study found that only 15 percent of teens reported actually getting the minimum hours of sleep on school nights.
After puberty, adolescents experience a natural shift in their internal clock and usually are unable to fall asleep until 11 p.m. or later. This shift becomes exaggerated for up to one in six teenagers, resulting in a disorder called delayed sleep phase syndrome. Teens with this syndrome are not able to get to sleep until well past midnight.
"Biologically, they are more prone to have it happen because of changes in their circadian rhythm, but then they make it worse for themselves by staying up late," said William Kohler, MD, medical director of the Florida Sleep Institute in Spring Hill, Fla. "Their biological clock gets reset to a later hour. A student stays up late and sleeps to noon on the weekend, [so] his brain has reset the clock later, and he's not going to be able to get the sleep he needs for the school day."
Adults and Sleep
Adults typically need 7 to 9 hours of sleep a night, but this can vary widely from person to person. "There's no absolute number," Dr. Kohler said. "Some people only need 4 or 5 hours of sleep; others need 9 to 10 hours."
This variability means that adults need to pay attention to their rhythms and figure out the amount of sleep that's right for them. They need to determine for themselves the length of sleep that leaves them feeling refreshed and alert throughout the day.
Adulthood also is the time when some people begin experiencing sleep disorders that will keep them from getting full rest. Problems like restless legs syndrome, sleep apnea, and insomnia crop up as people age. Other problems are particular to women, who may have sleep disruptions during menstruation, pregnancy, and menopause.
"You may get the quantity of sleep you need, but if your sleep is interrupted, the quality may not be there, and you need both the quality and quantity of sleep to function your best," Kohler said.
Seniors and Sleep
Sleep disorders become more common as people age because some chronic conditions have side effects that can disrupt seniors' sleep. Because they are less able to maintain quality sleep, seniors tend to suffer chronic sleep deprivation that causes them to nod off during the day.
Seniors are also more likely to experience a natural shift in their internal clock that doctors call advanced sleep phase syndrome, in which they begin going to bed earlier and getting up earlier in the morning.
There is some evidence that seniors do not need as much sleep as younger adults. A 2013 study published in the Journal of Clinical Sleep Medication found that seniors are mentally sharper if they got only 6 to 8 hours of sleep. Study participants who slept 9 or more hours did worse on tests.
"It's becoming more and more clear that as we age, we need less and less sleep," Drake said. "It's not a huge effect, but it's something that's becoming well established in the literature. It may have something to do with the fact that we need less of that developmental brain power that occurs as we sleep."