Age-related change in the relationship between circadian period, circadian phase, and diurnal preference in humans.

Aging is associated with specific sleep complaints, including earlier awakening and decreased sleep consolidation at the end of the night. The circadian pacemaker influences sleep timing and consolidation, and it has been hypothesized that a change in the circadian timing system may contribute to age-related changes in sleep. Here, we examined the relationship between circadian period and wake time, circadian phase, and diurnal preference (morningness-eveningness) in older subjects, and found no significant correlation between those measures, in contrast to our findings from young subjects. These results provide further evidence that the interaction between the circadian system and sleep-wake timing is altered in aging, and suggest that a shortening of circadian period with age cannot account for the advanced circadian phase and earlier wake times of older subjects.