The time spent actually sleeping out of eight hours in bed declined progressively and significantly with age, the study published in SLEEP, the official journal of the American Academy of Sleep Medicine and the Sleep Research Society, said.
Older adults, aged 66-83, slept about 20 minutes less than middle-aged adults (40-55 years), who slept 23 minutes less than young adults aged 20-30, the study said.
The older adults woke up significantly more often and spent more time awake after initial sleep onset than younger adults.
Deep, or slow-wave sleep, thought to be the most restorative phase of sleep, decreased with age, the study said.
But although older adults slept less deeply and less overall, and their sleep was less continuous than their younger counterparts’, they also showed less need for a quick kip during the day.
The study was conducted at the Clinical Research Centre of the University of Surrey in England and involved 110 healthy adults without sleep disorders or complaints.
Forty-four of the participants were young, 35 middle-aged and 31 older adults.
They slept normally one night, the baseline night, then had two nigths where their sleep was interrupted, followed by one recovery night.
During the baseline night, younger adults spent an average of 433.5 minutes asleep compared to around 410 minutes for middle aged adults and 390 for older adults.
On the same night, the younger adults had 118.4 minutes of deep sleep, compared to 85.3 minutes for middle-aged adults and 84.2 minutes for older adults.
But when asked to lie in a comfortable position on a bed during the day and try to fall asleep, young adults nodded off in an average of 8.7 minutes, compared with nearly 12 minutes for middle-aged adults and just over 14 minutes for older adults.