Effects of a month-long napping regimen in older individuals

Abstract

Objectives: To examine the effects of a month-long nap regimen using one of two durations (45 minutes or 2 hours) on nighttime sleep and waking function in a group of healthy older participants and to assess the degree to which healthy older individuals are willing and able to adhere to such napping regimens.

Design: Three laboratory sessions, with 2-week at-home recording interspersed, using a between-participants approach.

Setting: Laboratory of Human Chronobiology at Weill Cornell Medical College and participants' homes.

Participants: Twenty-two healthy men and women aged 50 to 88 (mean 70).

Measurements: Polysomnography (sleep electroencephalography), actigraphy, sleep diaries, neurobehavioral performance, sleep latency tests.

Results: With the exception of adherence to the protocol, there were few differences between short and long nap conditions. Napping had no negative effect on subsequent nighttime sleep quality or duration, resulting in a significant increase in 24-hour sleep amounts. Such increased sleep was associated with enhanced cognitive performance but had no effect on simple reaction time. Participants were generally able to adhere better to the 45-minute than the 2-hour nap regimen.

Conclusion: A month-long, daily nap regimen may enhance waking function without negatively affecting nighttime sleep. Using 2-hour naps in such a regimen is unlikely to meet with acceptable adherence; a regimen of daily 1-hour naps may be more desirable for effectiveness and adherence.

Figure 1

Post-nap nighttime polysomnographic sleep variables for Short and Long conditions at (a) mid and (b) end laboratory sessions. Sleep stage percentages, including wakefulness after sleep onset, are expressed as a percentage of the interval from sleep onset to wakeup time, or sleep period time (SPT). The duration of nighttime SPT varied among subjects but did not differ between Short and Long groups. A mixed MANOVA (Condition × Session, including all sleep stage percentage variables), n.s. No main effects for Condition or Session, and no interaction effects.

Figure 2

Polysomnographic sleep variables from naps for Short and Long conditions at (a) mid and (b) end laboratory sessions. Minutes to sleep onset (SOL) and minutes of each sleep stage, including wakefulness after sleep onset (WASO) are presented. Nap opportunity duration was 45 minutes for Short and 120 minutes for Long. Asterisks denote significant differences between conditions (** p < .001; * p < .05).

Figure 3

Total sleep time per 24 hours (tst/24hr). A mixed ANOVA (Condition × Session) revealed a main effect for Session (p<0.02) and Condition × Session interaction (p<0.05). Post-hoc comparisons indicated that tst/24hr in Long group increased significantly from baseline to mid and baseline to end, tst/24hr in Short group increased significantly from baseline to end only, and tst/24hr in the Long group was significantly greater than in the Short group at the mid Session (p<0.05), but not at the end Session.

Figure 4

Throughput ([accuracy × speed] × 100) on 4 neurobehavioral performance tasks (a–d). Top portion of each graph shows % change from baseline for Short (- - • - -) and Long (— ■ —) conditions. Bottom portion of each graph shows absolute levels of throughput for Short (open bars) and Long (solid bars) conditions. Multivariate ANOVAs for Condition × Session including all 4 tasks revealed no main effect for Condition, a significant main effect for Session (Wilks lambda p < 0.01), and no Condition × Session interaction. Univariate ANOVAs indicated that throughput increased significantly across Sessions for all but d) Two Choice Reaction Time. Post-hoc comparisons indicated that throughput increases were significant from baseline to mid, mid to end, and baseline to end on each of the other three tasks.