Age-Related Reduction in the Maximal Capacity for Sleep

From Current Biology:

Sleep changes markedly across the life span and complaints about insomnia are prevalent in older people [1].
Whether age-related alterations in sleep are due to modifications in
social factors, circadian physiology, homeostatic drive, or the ability
to sleep remains unresolved. We assessed habitual sleep duration at
home and then quantified daytime sleep propensity, sleep duration, and
sleep structure in an inpatient protocol that included extended sleep
opportunities covering 2/3 of the circadian cycle (12 hr at night and 4
hr in the afternoon) for 3–7 days in 18 older and 35 younger healthy
men and women. At baseline, older subjects had less daytime sleep
propensity than did younger subjects. Total daily sleep duration, which
was initially longer than habitual sleep duration, declined during the
experiment to asymptotic values that were 1.5 hr shorter in older (7.4
± 0.4 SEM, hour) than in younger subjects (8.9 ± 0.4).
Rapid-eye-movement sleep and non-rapid-eye-movement sleep contributed
about equally to this reduction. Thus, in the absence of social and
circadian constraints, both daytime sleep propensity and the maximal
capacity for sleep are reduced in older people. These data have
important implications for understanding age-related insomnia.