Effects of daytime naps on procedural and declarative memory in patients with schizophrenia

Sleep has been identified as a state that optimizes the consolidation of newly acquired information in memory. Straight memory deficits and sleep disturbances are well-known in patients with schizophrenia. This study tested the hypothesis that patients with schizophrenia have a deficit in procedural and declarative memory consolidation after a short midday nap when compared to healthy controls and patients with remitted to moderate major depression.Following a normal night’s sleep, 22 healthy subjects, 20 patients with major depression and 21 patients with schizophrenia were studied in a napping and wake condition in a random-order cross-over design, early in the afternoon. To test declarative memory, the Rey-Osterrieth Complex Figure Test respectively the Taylor Complex Figure Test and, for procedural learning, a mirror tracing task were performed.The present study is the first to demonstrate significant differences between individuals with schizophrenia, depression and healthy matched controls with regard to measures of sleep and memory performance after a short period of daytime sleep (napping). In particular we found that a daytime nap of only about 40 min led to improvement of declarative memory performance in all investigated groups, whereas no beneficial effect was seen on procedural performance in the group of medicated patients with schizophrenia in contrast to healthy controls and patients with remitted to moderate major depression.     

中国中老年人午睡时长与抑郁症状的关联——基于CHARLS数据分析

目的 探究午睡时长与中老年人抑郁症状发生的关联。方法 将2011年中国健康与养老追踪调查(China Health and Retirement Longitudinal Study, CHARLS)调查的45岁及以上的中老年人信息作为基线数据,随访该队列至2018年,采用COX比例风险模型分析不同午睡时长与中老年人抑郁症状发生的关联。结果 该队列随访期间抑郁症状的发生率为6.94%。COX比例风险模型结果表明,午睡≥90 min/d与抑郁症状发生高风险相关(HR=1.14;95%CI:1.02～1.29);亚组分析结果显示,男性午睡时长≥90 min/d(HR=1.30;95%CI:1.11～1.53)、45～64岁组午睡时长在60～89 min/d(HR=1.14;95%CI:1.01～1.29)及≥90 min/d(HR=1.17;95%CI:1.02～1.34)与抑郁症状发生高风险相关。结论 午睡时长与中老年人抑郁症状发生相关联,特别是在男性及中年人群体中。     

Habitual napping moderates motor performance improvements following a short daytime nap

The effect of napping on motor performance was examined in habitual and non-habitual nappers who were randomly assigned to a nap or reading condition. Motor procedural learning and auditory discrimination tasks were administered pre- and post-condition. Both groups reported improved alertness post-nap, but not post-reading. Non-habitual nappers fell asleep faster and tended to have greater sleep efficiency, but did not differ from habitual nappers on other sleep architecture variables. Habitual nappers had greater alpha and theta EEG power in stage 1, and greater delta, alpha and sigma power in stage 2 sleep. Motor performance deteriorated for non-habitual nappers who napped, but improved for all others. The number of sleep spindles and sigma power (13.5-15 Hz) significantly predicted motor performance following the nap, for habitual nappers only. Results indicate that motor learning was consolidated in a brief nap and was associated with stage 2 spindles, but only for those who habitually take naps.     

Napping Is Associated with Increased Risk of Type 2 Diabetes: The Guangzhou Biobank Cohort Study

Study Objective:

Intentional napping is very common, particularly in China. However, there are limited data regarding its potential health effects. We therefore examined the possible relationship between napping and type 2 diabetes.

Design:

Cross-sectional analysis of baseline data from the Guangzhou Biobank Cohort Study.

Setting:

Community-based elderly association in Guangzhou, China.

Participants:

19,567 Chinese men and women aged 50 years or older.

Measurements and Results:

Self-reported frequency of napping was obtained by questionnaire and type 2 diabetes was assessed by fasting blood glucose and/or self-reports of physician diagnosis or treatment. Participants reporting frequent naps (4-6 days/week and daily) were 42% to 52% more likely to have diabetes. The relationships remained essentially unchanged after adjustments were made for demographics, lifestyle and sleep habits, health status, adiposity, and metabolic markers (odds ratio for diabetes 1.36 [95% CI 1.17–1.57] in 4-6 days/week, 1.28 [1.15–1.44] in daily nappers). Similar associations were found between napping and impaired fasting glucose. Removal of those with potential ill health and daytime sleepiness did not alter the observed associations.

Conclusions:

Napping is associated with elevated prevalence of diabetes and impaired fasting glucose in this older Chinese sample. Our finding suggests that it is less likely that diabetes leads to daytime sleepiness. This raises the possibility that napping may increase the risk of diabetes. Confirmation by longitudinal studies is needed.

Citation:

Lam KbH; Jiang CQ; Thomas GN; Arora T; Zhang WS; Taheri S; Adab P; Lam TH; Cheng KK. Napping is associated with increased risk of type 2 diabetes: the Guangzhou Biobank Cohort Study. SLEEP 2010;33(3):402-407.     

中国15～69岁居民睡眠状况分析

目的了解我国15～69岁居民睡眠状况。方法使用2007年中国慢性病及其危险因素监测数据,对50368名居民的睡眠时间和午睡时间进行分析。结果我国15-69岁居民每天的睡眠时间为（8．1±1．3）h,其中15—29、30～39、40-49、50-59和60～69岁居民的每天睡眠时间分别为8．3、8．1、8．0、7．8和7．7h。不同年龄、地区和性别的睡眠时间均为城市低于农村（P〈0．0．5）。60．7％的人没有午睡习惯,30．4％的人午睡时间不超过1h,8．9％的人午睡时间在1h以上。不午睡人群的比例,女性（62．5％）高于男性（59．1％）;农村（65．0％）高于城市（54.3％）;西部地区（66．6％）高于中部（58．1％）和东部地区（58．8％）,各组比较的P值均〈0．05。结论我国城市居民睡眠时间少于农村居民,午睡人群的比例减少,需进一步开展研究来探讨睡眠与慢病的关系。     

Daytime napping and its effects on alertness and short-term memory performance in shiftworkers

Summary Daytime napping and its effects on 145 female shiftworkers were studied by comparing the individual characteristics, alertness, and short-term memory performance of subjects who took or did not take naps. Of the subjects 56% (n = 82) took a nap before a night shift and 21% (n = 30) after a morning shift. After a morning shift, napping was more frequent among evening types and subjects living alone (not married). Before a night shift, daytime napping was not connected to individual characteristics, but the total sleep time of nappers during the preceding night was shorter than that of non-nappers. At 10.00 and at 04.00–08.00, at the end of the night shift, nappers were significantly more alert than subjects who had not taken naps. The length and timing of the daytime nap did not correlate to either alertness or performance during the following night. In a questionnaire, nappers before a night shift had less sleep disturbances than non-nappers.     

Objective napping,cognitive decline,and risk of cognitive impairment in older men

IntroductionLittle is known about the longitudinal association between napping and cognitive impairment in older adults.MethodsWe used wrist actigraphy to measure naps in 2751 community-dwelling older men. Cognition was assessed repeatedly over 12 years, and clinically significant cognitive impairment was determined by physician diagnosis, Alzheimer's medication use or a significant cognitive decline.ResultsAfter adjustment for all covariates, men with longer napping duration had greater cognitive decline and higher risk of cognitive impairment. Men who napped for ≥120 min/day (vs. <30 min/day) were 66% more likely to develop cognitive impairment (odds ratio = 1.66, 95% CI: 1.09–2.54) in 12 years. Further adjustment for nighttime sleep quality did not appreciably alter the results. The association between napping and cognitive impairment was more pronounced among those with higher sleep efficiency and average sleep duration.DiscussionNapping might be useful as an early marker of cognitive impairment in the elderly, and its cognitive effects may differ by nighttime sleep.     

A review of short naps and sleep inertia: do naps of 30 min or less really avoid sleep inertia and slow-wave sleep?

ObjectivesNapping is a widely used countermeasure to sleepiness and impaired performance caused by sleep loss and circadian pressure. Sleep inertia, the period of grogginess and impaired performance experienced after waking, is a potential side effect of napping. Many industry publications recommend naps of 30 min or less to avoid this side effect. However, the evidence to support this advice is yet to be thoroughly reviewed.MethodsElectronic databases were searched, and defined criteria were applied to select articles for review. The review covers literature on naps of 30 min or less regarding (a) sleep inertia, (b) slow-wave sleep (SWS) and (c) the relationship between sleep inertia and SWS.ResultsThe review found that although the literature on short afternoon naps is relatively comprehensive, there are very few studies on naps of 30 min or less at night. Studies have mixed results regarding the onset of SWS and the duration and severity of sleep inertia following short naps, making guidelines regarding their use unclear. The varying results are likely due to differing sleep/wake profiles before the nap of interest and the time of the day at waking.ConclusionsThe review highlights the need to have more detailed guidelines about the implementation of short naps according to the time of the day and prior sleep/wake history. Without this context, such a recommendation is potentially misleading. Further research is required to better understand the interactions between these factors, especially at night, and to provide more specific recommendations.     

Cognitive deficit is associated with phase advance of sleep–wake rhythm, daily napping, and prolonged sleep duration—a cross-sectional study in 2,947 community-dwelling older adults

This study aims to examine the phase advance of sleep–wake rhythm, napping habit, nocturnal sleep duration, prolonged sleep latency and insomnia and their relationship with cognitive function. This is a cross-sectional study. Participants in this study are 2,947 community-dwelling adults older than 65 years old. Measurements of mini-mental examination (MMSE) score, go-to-bed time, wake-up time, nocturnal sleep duration, prolonged sleep latency, napping, and insomnia were done. The mean (standard deviation) nocturnal sleep hours was 7.96 (1.39) h. Twenty-one percent and 16.2% of the participants complained of prolonged sleep latency longer than 1 h and insomnia, respectively. Fifty-six percent of the participants napped once or more than once weekly. With advancing age, the participants reported longer sleep duration (p < 0.001), went to bed earlier, and woke up earlier, which were significant both before and after adjustment. The participants who had lower MMSE score went to bed earlier and woke up earlier, which were statistically significant both before and after adjustment. An inverted U-shaped relationship was observed between MMSE score and napping frequency, p for tend 0.026.The MMSE score decreased when the sleep duration prolonged from 7 h to ≧10 h (p for trend 0.006). No trend was observed from the sleep duration <4 up to 7.9 h (p for trend 0.500). Modest age-independent phase advance of the sleep–wake rhythm is associated with lower cognitive function. Whether this is a manifestation of early pre-clinical dementia and whether its recognition with early stabilization can slow cognitive decline remain elusive.     

Association between nighttime sleep and napping in older adults

STUDY OBJECTIVES: Napping might indicate deficiencies in nighttime sleep, but the relationship is not well defined. We assessed the association of nighttime sleep duration and fragmentation with subsequent daytime sleep. DESIGN: Cross-sectional study. PARTICIPANTS: 235 individuals (47.5% men, 29.7% black), age 80.1 (2.9) years. MEASUREMENTS AND RESULTS: Nighttime and daytime sleep were measured with wrist actigraphy and sleep diaries for an average of 6.8 (SD 0.7) nights. Sleep parameters included total nighttime sleep (h), movement and fragmentation index (fragmentation), and total daytime sleep (h). The relationship of total nighttime sleep and fragmentation to napping (yes/no) was assessed using logistic regression. In individuals who napped, mixed random effects models were used to determine the association between the previous night sleep duration and fragmentation and nap duration, and nap duration and subsequent night sleep duration. All models were adjusted for age, race, gender, BMI, cognitive status, depression, cardiovascular disease, respiratory symptoms, diabetes, pain, fatigue, and sleep medication use. Naps were recorded in sleep diaries by 178 (75.7%) participants. The odds ratios (95% CI) for napping were higher for individuals with higher levels of nighttime fragmentation (2.1 [0.8, 5.7]), respiratory symptoms (2.4 [1.1, 5.4]), diabetes (6.1 [1.2, 30.7]), and pain (2.2 [1.0, 4.7]). Among nappers, neither sleep duration nor fragmentation the preceding night was associated with nap duration the next day. CONCLUSION: More sleep fragmentation was associated with higher odds of napping although not with nap duration. Further research is needed to determine the causal association between sleep fragmentation and daytime napping.