Healthy Adults May Need
Less Sleep As They Age
A study in the Feb. 1 issue of the journal SLEEP suggests that healthy
older adults without sleep disorders can expect to have a reduced
"sleep need" and to be less sleepy during the day than
healthy young adults.
Results show that during a night of eight hours in bed, total
sleep time decreased significantly and progressively with age.
Older adults slept about 20 minutes less than middle-aged adults,
who slept 23 minutes less than young adults. The number of awakenings
and the amount of time spent awake after initial sleep onset increased
significantly with age, and the amount of time spent in deep,
slow-wave sleep decreased across age groups. Yet even with these
decreases in sleep time, intensity and continuity, older adults
displayed less subjective and objective daytime sleep propensity
than younger adults.
Furthermore, two additional nights involving experimental disruption
of slow-wave sleep led to a similar response in all age groups.
Daytime sleep propensity increased, and slow-wave sleep rebounded
during a night of recovery sleep. According to the authors, this
suggests that the lack of increased daytime sleepiness in the
presence of an age-related deterioration in sleep quality cannot
be attributed to unresponsiveness to variations in homeostatic
sleep pressure. Instead, healthy aging appears to be associated
with reductions in the sleep duration and depth required to maintain
"Our findings reaffirm the theory that it is not normal
for older people to be sleepy during the daytime," said principal
investigator Derk-Jan Dijk, PhD, professor of sleep and physiology
at the University of Surrey in the U.K. "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."
The study was conducted at the Clinical Research Centre of the
University of Surrey and involved 110 healthy adults without sleep
disorders or sleep complaints; 44 were young (20 to 30 years),
35 were middle-aged (40 to 55 years) and 31 were older adults
(66 to 83 years). After an eight-hour baseline sleep test, subjects
were randomized to two nights with or without selective slow-wave
sleep disruption by acoustic stimuli, followed by one recovery
night. Nighttime sleep was evaluated by polysomnography, while
sleep propensity was assessed using the Multiple Sleep Latency
Test (MSLT) and the Karolinska Sleepiness Scale.
During the baseline night, mean objective total sleep time decreased
from 433.5 minutes for young adults to 409.9 minutes for middle-aged
adults and 390.4 minutes for older adults. Average minutes of
slow-wave sleep decreased from 118.4 minutes for young adults
to 85.3 minutes for middle-aged adults and 84.2 minutes for older
adults. Mean number of minutes spent awake after initial sleep
onset increased from 21 for young adults to 49.9 for middle-aged
adults and 70.7 for older adults.
Objective daytime sleepiness measured by the MSLT decreased with
age. When asked to lie in a comfortable position on the bed and
try to fall asleep, young adults fell asleep in an average of
8.7 minutes, compared with 11.7 minutes for middle-aged adults
and 14.2 minutes for older adults.
The authors noted that the cause of the age-related reductions
in slow-wave sleep and sleep need still must be established. Related
factors could include alterations in reproductive hormones or
changes in the brain. They added that the study did not address
sleep propensity during the evening hours, when it is possible
that older adults may be sleepier than young adults.
According to the authors, the study also has implications for
the treatment of insomnia in older adults, who may be unaware
of their reduced sleep need. Therefore, sleep restriction, which
leads to increased homeostatic sleep pressure, may be a successful
behavioral therapy for insomnia in healthy older adults.
February 2, 2010