A new study shows that during a standard night of eight hours in bed the amount of time spent actually sleeping decreases progressively with age. Healthy older adults sleep about 20 minutes less than middle-aged adults, who sleep 23 minutes less than young adults.
Researchers say the results suggest that healthy older adults without sleep disorders should expect to sleep a little less at night without being sleepy during the day.
"Our findings reaffirm the theory that it is not normal for older people to be sleepy during the daytime," researcher Derk-Jan Dijk, PhD, professor of sleep and physiology at the University of Surrey in England, says in a news release. "Whether you are young or old, if you are sleepy during the day you either don't get enough sleep or you may suffer from a sleep disorder."
Less Sleep Part of Healthy Aging
The study, published in Sleep, involved 110 healthy adults without sleep complaints who were studied for one normal eight-hour sleep night followed by two nights with or without sleep disruption followed by one recovery night.
Among the participants, 44 were young (20 to 30 years old), 35 were middle-aged (40 to 55) and 31 were older adults (66 to 83). Their sleep was evaluated by polysomnography and monitored by researchers throughout the experiment.
During the first normal sleep session, young adults slept an average of 433.5 minutes, middle-aged adults slept 410 minutes, and older adults slept 390 minutes. The average number of minutes spent in deep, slow-wave sleep also decreased with age.
In addition, the average number of minutes spent awake after initially falling asleep increased from 21 for young adults to 50 for middle-aged adults and 71 for older adults.
Even though older adults got less total sleep at night than their younger counterparts, researchers found that older adults displayed fewer symptoms of daytime sleepiness. In a measure of daytime sleepiness, older adults took five-and-a-half minutes longer to fall asleep after lying down compared to younger adults.
The second part of the study, which involved disrupting the participants' sleep, led to a similar response among the three age groups. They all showed more signs of daytime sleepiness, and deep, slow-wave sleep rebounded during the night of recovery sleep.
Researchers say healthy aging appears to be associated with a natural reduction in sleep duration and depth needed to maintain daytime alertness. They say the cause for age-related reduction in sleep still needs to be established, but the findings could have important implications for older adults complaining of insomnia who may not be aware of their reduced need for sleep.