Effects of a two-hour change in bedtime on the sleep of healthy seniors.

Some of the sleep disruption seen in seniors (>65 yrs) may be due to alteration of the circadian pacemaker phase and/or its phase angle with bedtime. The purpose of this study was to determine the effects of 2 h changes in the timing of bedtime (both earlier and later) on the sleep of seniors. Ten healthy seniors (9 F, 1 M, age 70-82 yrs) were each studied individually during three 120 h sessions (each separated by >2 weeks) in a time-isolation laboratory. On nights 1 and 2, bedtime and rise-time occurred at the subjects' habitual times; on nights 3-5, bedtime was specified by the experiment, but rise-time was at the subjects' discretion (without knowledge of clock time). Under the control condition, subjects went to bed at their habitual bedtime (HBT), under the earlier bedtime condition at (HBT-2 h), and under the later bedtime condition at (HBT+2 h). Sleep was polysomnnographically recorded and rectal temperature continuously monitored. Although total sleep time increased in the earlier compared to the later condition (p<0.01), sleep efficiency decreased and wake after sleep onset increased (p<0.01). Subjective ratings of sleep were also worse under the earlier (HBT-2 h) than under later (HBT+ 2 h) condition (p<0.05). Performance did not differ between the earlier and later conditions. The larger the phase angle between actual bedtime and circadian temperature minimum (Tmin), the longer the time spent in bed and total sleep time, and the worse the sleep efficiency and subjective sleep ratings. There were no effects related to the phase angle between Tmin and rise-time. The relative benefits of longer vs. more efficient sleep in the elderly require further investigation.