Sleep duration and the risk of new-onset arthritis in middle-aged and older adult population: results from prospective cohort study in China.

Background: The pain and sleep disorders caused by arthritis are health issues that have been re-emphasized with the aging population. However, the majority of research on arthritis and sleep disorders has focused on cases that have already been diagnosed with arthritis. This research aims to explore the correlation between sleep duration and new-onset arthritis in middle-aged and older adult individuals. Methods: Utilizing data from the China Health and Retirement Longitudinal Study from baseline (2011) to the Wave 3 follow-up (2018), we conducted a 7-year longitudinal investigation targeting populations with valid sleep questionnaire records and without arthritis. Sleep duration was assessed from nighttime sleep and daytime nap records. The new-onset of arthritis was determined based on self-reported diagnosis. We employed different logistic regression models to consider the potential impact of sleep duration on arthritis and conducted mediation analyses to assess the involvement of BMI in the association between sleep duration and the new-onset risk of arthritis. Results: Out of the 6,597 individuals analyzed in the cohort, 586 (8.9%) were diagnosed with new-onset arthritis. Median sleep duration was notably shorter in the new-onset arthritis group (6.63 vs. 6.41 h, p < 0.05). There was a notable negative correlation found between new-onset risk of arthritis and sleep duration, with each Interquartile Range (IQR) increment in sleep leading to a 16% risk reduction (OR: 0.864; 95% CI: 0.784-0.954). Stratified analyses revealed BMI as a potential modifier in the sleep-arthritis relationship (P for interaction = 0.05). Mediation analyses further showed that about 3.5% of the association was mediated by BMI. Additionally, the inclusion of sleep duration improved the arthritis predictive power of our model, with an IDI of 0.105 (0.0203, 0.1898) and an NRI of 0.0013 (0.0004, 0.0022) after adding sleep duration to the basic model. Conclusion: In the middle-aged and older adult demographic of China, increased sleep duration is associated with a decreased new-onset risk of arthritis, with BMI potentially playing a role in mediating this connection.

A daytime nap with REM sleep is linked to enhanced generalization of emotional stimuli.

How memory representations are shaped during and after their encoding is a central question in the study of human memory. Recognition responses to stimuli that are similar to those observed previously can hint at the fidelity of the memories or point to processes of generalization at the expense of precise memory representations. Experimental studies utilizing this approach showed that emotions and sleep both influence these responses. Sleep, and more specifically rapid eye movement sleep, is assumed to facilitate the generalization of emotional memories. We studied mnemonic discrimination by the emotional variant of the Mnemonic Separation Task in participants (N = 113) who spent a daytime nap between learning and testing compared with another group that spent an equivalent time awake between the two sessions. Our findings indicate that the discrimination of similar but previously not seen items from previously seen ones is enhanced in case of negative compared with neutral and positive stimuli. Moreover, whereas the sleep and the wake groups did not differ in memory performance, participants entering rapid eye movement sleep exhibited increased generalization of emotional memories. Our findings indicate that entering into rapid eye movement sleep during a daytime nap shapes emotional memories in a way that enhances recognition at the expense of detailed memory representations.

Excessive daytime napping independently associated with decreased insulin sensitivity in cross-sectional study - Hyogo Sleep Cardio-Autonomic Atherosclerosis cohort study.

Background: Although excessive daytime napping has been shown to be involved in diabetes occurrence, its impact on insulin secretion and sensitivity has not been elucidated. It is speculated that excessive napping disrupts the sleep-wake rhythm and increases sympathetic nerve activity during the day, resulting in decreased insulin sensitivity, which may be a mechanism leading to development of diabetes. We previously conducted a cross-sectional study that showed an association of autonomic dysfunction with decreased insulin sensitivity, though involvement of autonomic function in the association between napping and insulin sensitivity remained unclear. Furthermore, the effects of napping used to supplement to short nighttime sleep on insulin secretion and sensitivity are also unknown. In the present cross-sectional study, we examined the relationships of daytime nap duration and autonomic function with insulin secretion and sensitivity in 436 subjects enrolled in the Hyogo Sleep Cardio-Autonomic Atherosclerosis (HSCAA) Cohort Study who underwent a 75-g oral glucose tolerance test (75-g OGTT), after excluding those already diagnosed with diabetes. Methods: Daytime nap duration was objectively measured using actigraphy, with the subjects divided into the short (≤1 hour) and long (>1 hour) nap groups. Insulin secretion and sensitivity were determined using 75-g OGTT findings. Standard deviation of normal to normal R-R interval (SDNN), a measure of autonomic function, was also determined based on heart rate variability. Subgroup analysis was performed for the associations of napping with insulin secretion and sensitivity, with the results stratified by nighttime sleep duration of less or greater than six hours. Results: Subjects in the long nap group exhibited lower insulin sensitivity parameters (QUICKI: ß=-0.135, p<0.01; Matsuda index: ß=-0.119, p<0.05) independent of other clinical factors. In contrast, no associations with insulin secretion were found in either group. Furthermore, the association of long nap duration with insulin sensitivity was not confounded by SDNN. Specific subgroup analyses revealed more prominent associations of long nap habit with lower insulin sensitivity in subjects with a short nighttime sleep time (ß=-0.137, p<0.05). Conclusion: Long daytime nap duration may be a potential risk factor for decreased insulin sensitivity.

Effects of a brief afternoon nap on declarative and procedural memory.

The relationship between sleep and memory consolidation has not been fully revealed. The current study aimed to investigate how a brief afternoon nap contributed to the consolidation of declarative and procedural memory by exploring the relationship between sleep characteristics (i.e., the durations of sleep stages and slow oscillation, slow-wave activity, and spindle activity extracted from sleep) and task performance and the relationship between delta, theta, alpha, and beta bands extracted from wake during task performance and task performance. Twenty-three healthy young adults underwent a paired associates learning task and a sequential finger-tapping task with easy and difficult levels and were tested for memory performance before and after the intervention (i.e., an about 30-min nap or stay awake). Electroencephalogram (EEG) signals were continously recorded during the whole experiment. Results revealed that a short afternoon nap improved movement speed for the procedural memory task, regardless of the task difficulty, but unaffected the performance on the declarative memory task. Besides, the improvement in movement speed for the easy procedural memory task was positively correlated with slow-wave activity (SWA) during non-rapid-eye-movement (NREM) sleep but negatively correlated with slow oscillation and spindle activity during sleep stage 2 and NREM sleep, and the improvement in the difficult procedural memory task correlated positively with SWA during NREM sleep. Moreover, performance on the easy declarative and procedural memory tasks was negatively correlated with the relative power of alpha or theta; whereas the alpha band was positively correlated with the difficult declarative memory performance. These findings suggested that a brief afternoon nap with NREM sleep would benefit procedural memory consolidation but not declarative memory; such contribution of napping to memory consolidation would be either explained by the sleep characteristics or physiological arousal during performing tasks; task difficulty would moderate the relationship between the declarative memory performance and EEGs during task performance.

Daytime naps and depression risk: A meta-analysis of observational studies.

Background: The relationship between daytime napping and depression remains debatable. Thus, a meta-analysis in this study was conducted to evaluate the relationship between daytime napping and depression. Methods: The PubMed, Embase, Web of Science, and China National Knowledge Infrastructure databases were searched up to February 2022, and the reference lists of the included studies were also retrieved. A random-effects model was used to estimate the combined effect size. Results: Nine studies with 649,111 participants were included in the final analysis. The pooled odds ratio (OR) was 1.15 (95% confidence interval: 1.01-1.31) with a significant heterogeneity (I 2 = 91.3%, P for heterogeneity <0.001), and the results demonstrated an increased risk of depressive symptoms among daytime nappers. Visual inspection of the funnel plot and Egger's and Begg's tests identified no obvious evidence of publication bias. Conclusion: This meta-analysis indicates that daytime naps are a predictor of depression. The effects of daytime napping on depression may vary depending on the characteristics of people, the pattern of naps, and the individual's sleep experience. The findings may have significant implications for future research on depression.

Effects of a Short Daytime Nap on the Cognitive Performance: A Systematic Review and Meta-Analysis.

BACKGROUND: Napping in the workplace is under debate, with interesting results on work efficiency and well-being of workers. In this systematic review and meta-analysis, we aimed to assess the benefits of a short daytime nap on cognitive performance. METHODS: PubMed, Cochrane Library, ScienceDirect and PsycInfo databases were searched until 19 August 2021. Cognitive performance in working-aged adults, both before and following a daytime nap or under control conditions (no nap), was analysed by time and by type of cognitive function (alertness, executive function and memory). RESULTS: We included 11 studies (all in laboratory conditions including one with a subgroup in working conditions) for a total of 381 participants. Mean duration of nap was 55.4 ± 29.4 min. Overall cognitive performance did not differ at baseline (t0) between groups (effect size -0.03, 95% CI -0.14 to 0.07), and improved in the nap group following the nap (t1) (0.18, 0.09 to 0.27), especially for alertness (0.29, 0.10 to 0.48). Sensitivity analyses gave similar results comparing only randomized controlled trials, and after exclusion of outliers. Whatever the model used, performance mainly improved until 120 min after nap, with conflicting results during the sleep inertia period. Early naps in the afternoon (before 1.00 p.m.) gave better cognitive performance (0.24, -0.07 to 0.34). The benefits of napping were independent of sex and age. Duration of nap and time between nap and t1 did not influence cognitive performance. CONCLUSIONS: Despite the fact that our meta-analyses included almost exclusively laboratory studies, daytime napping in the afternoon improved cognitive performance with beneficial effects of early nap. More studies in real work condition are warranted before implementing daytime napping at work as a preventive measure to improve work efficiency.

The role of daytime napping in declarative memory performance: a systematic review.

Sleep plays an important role in stabilizing and reinforcing memory of newly acquired information. Like nocturnal sleep, a daytime nap is shown to effectively contribute to memory processing. However, studies are often focused on nocturnal sleep. This review has aimed at systematically compiling the results of studies which have examined the effects of napping on declarative memory performance in healthy adults. Such studies have focused on different aspects of memory reinforcement following a diurnal nap including the involved mechanisms in memory reconsolidation, type of declarative tasks, cross-gender differences, the role of age, duration of nap and its delayed onset. One of the reviewed studies reported that even as short as 6 min of napping exerts a positive effect on memory function. Evidence from these studies indicates hippocampal-dependent enhancement of the learned information. Diurnal naps predominantly include non-rapid eye movement sleep with slow waves yielding potential effects on declarative memory. Evidence has shown that the empowered learning and retrieval depends upon spindle density during the nap. Moreover, the role of coordinated autonomic and central events in enhancing declarative memory has also been reported. Slow waves and sleep spindles are known to fuel declarative memory function during the NREM-2 (N2) stage of sleep.

Mediation effect of platelet indices on the association of daytime nap duration with 10-year ASCVD risk.

Daytime nap is associated with the risk of atherosclerotic cardiovascular disease (ASCVD). However, the contribution of platelet to the association of daytime nap with ASCVD remains unclear. We analyzed the mediation effect of abnormal platelet indices on the association between daytime nap and 10-year ASCVD risk. The participants of this study were 2445 adults aged 30 to 74 years without ASCVD from the baseline Wuhan residents (n = 3053) of the Wuhan-Zhuhai (WHZH) Cohort Study. Participants completed the questionnaire and physical examination (including blood pressure, height, weight, and blood biochemical indicators). We assessed the association of daytime nap or nocturnal sleep duration with 10-year ASCVD risk and mediation effects of platelet indices on the associations using generalized linear models (GLM). Individuals with daytime nap duration of 30 or 60 min had a 1.37- (95%CI: 1.05, 1.78) or 1.44- (95%CI: 1.17, 1.78) fold increased risk of 10-year ASCVD compared with non-nappers. As compared with non-nappers, MPV values or MPV/PLT ratio mediated 15.29% or 6.18% of the association of daytime nap duration of 30 min with 10-year ADCVD risk as well as 19.21% or 7.61% of the association of daytime nap duration of 60 min with 10-year ADCVD risk (all p < .05). Platelet might partially contribute to increased 10-year ASCVD risk in individuals with daytime nap duration of 30 or 60 min.

The associations between different sleep patterns and osteoporosis based on the Osteoporosis Self-Assessment Tool for Asians.

Based on the use of Osteoporosis Self-Assessment Tool for Asians (OSTA) to assess osteoporosis risk, we found that short sleep duration and taking a daytime nap had an increased risk of osteoporosis. PURPOSE: To explore the associations between different sleep patterns with osteoporosis. METHODS: 3659 postmenopausal women (average age of 60 years) were divided into low, middle, and high osteoporosis risk categories based on the Osteoporosis Self-Assessment Tool for Asians (OSTA). After having collected by a standard questionnaire, total and nocturnal sleep duration was collapsed to form categories of ≤ 6 h, > 6 h and ≤ 7 h, > 7 h and ≤ 8 h, > 8 h and ≤ 9 h, > 9 h, and daytime nap duration of 0 h and > 0 h. RESULTS: As a categorical variable, the total sleep duration of ≤ 6 h per day (OR = 1.34, 95% CI 1.04-1.72), nocturnal sleep duration of ≤ 6 h per night (OR = 1.65, 95% CI 1.24-2.18), and taking a daytime nap (OR = 1.33, 95% CI 1.09-1.64) had higher osteoporosis risk after adjustment for covariates. As a continuous variable, after the adjustment for covariates, both longer total (OR = 0.86, 95% CI 0.78-0.94) and nocturnal sleep duration (OR = 0.83, 95% CI 0.76-0.91) had lower risk of osteoporosis risk while taking longer daytime nap (OR = 1.10, 95% CI 1.02-1.19) had higher osteoporosis risk. CONCLUSIONS: Postmenopausal women with both short total and nocturnal sleep duration (6 h or less) and taking a daytime nap had increased osteoporosis risk as assessed by OSTA.

Longitudinal Association Between Sleep Duration and Depressive Symptoms in Chinese Elderly.

AIM: This study aimed to evaluate the longitudinal association between sleep duration and depressive symptoms among the elderly in China. METHODS: A data set from China Health and Retirement Longitudinal Study (CHARLS) in 2011, 2013 and 2015 was adopted with a total of 22,847 respondents aged ≥60-years-old. A linear regression analysis with generalized estimating equations was employed to examine the longitudinal associations between duration of total sleep, nighttime sleep and daytime nap, and depressive symptoms. RESULTS: An extra hour of total sleep including nighttime sleep and daytime nap was associated with lower incidence of depressive symptoms among the elderly after adjusting all confounders (OR=0.83, 95% CI: 0.82-0.84). In addition, an extra hour of nighttime sleep (OR=0.82, 95% CI: 0.80-0.83) or daytime nap (OR=0.93, 95% CI: 0.89-0.97) was also negatively associated with depressive symptoms among the elderly. After controlling the total sleep time, an extra hour of nighttime sleep was negatively associated with depressive symptoms (OR=0.88, 95% CI: 0.84 to 0.92), while an extra hour of daytime nap displayed a positive association with depressive symptoms (OR=0.88, 95% CI: 0.84 to 0.92). Compared with the moderate nappers, only extended nappers had significantly higher incidence of depressive symptoms (OR=1.32, 95% CI: 1.19 to 1.45). CONCLUSION: For the elderly in China, increasing their total sleep, nighttime sleep, and/or daytime nap duration would reduce the incidence of depressive symptoms. Moreover, after fixing the total sleep time, increasing nighttime sleep was more beneficial to the decrease of the incidence of depressive symptoms than daytime nap.

A daytime nap restores hippocampal function and improves declarative learning.

STUDY OBJECTIVES: Daytime naps can confer benefits on subsequent declarative learning, but the physiological correlates of this improvement are less well studied. We examined learning following a daytime nap compared with an equivalent waking period using fMRI and polysomnography. METHODS: Forty healthy young adults who slept normally the previous night encoded word pair lists in an MRI scanner at 13:00 and 16:30. Between sessions, participants either stayed awake and watched a documentary (Wake Group; N = 20) or had a 90-minute nap opportunity (Nap Group; N = 20) monitored by polysomnography. Approximately 40 minutes after completing each encoding session, memory for learned words was assessed using cued-recall. RESULTS: A significant Session × Group interaction effect (p < 0.001) was observed in which memory was significantly improved in the Nap but not in the Wake group (p < 0.001). There was also a Session × Run × Group interaction effect in the left hippocampus (p = 0.001), whereby activation during word pair encoding increased only following the nap. Both performance improvement (rs = 0.46, p = 0.04) and nap-related increase in hippocampal activation (rs = 0.46, p = 0.04) were correlated with nap spindle count (12-15 Hz) but not with slow oscillation power (p's ≥ 0.18). CONCLUSIONS: After a habitual nocturnal sleep, participants who had a 90-minute afternoon nap encoded word pairs better than a comparable group who stayed awake. Increases in hippocampal activation following the nap suggest restored hippocampal function. Naptime spindles may contribute to improved memory.

[The effect of music containing binaural beats on daytime fall-asleep dynamics]. / Vliianie muzyki, soderzhashchei binaural'nye bieniia, na dinamiku dnevnogo zasypaniia.

AIM: To test the hypothesis that listening to the music with the effect of binaural beats of theta and delta range during nap decreases sleep latency defined by 2nd slow wave sleep stage appearance, as well as improves its stability. MATERIAL AND METHODS: The experimental set of 20 min duration was established according to the counterbalanced scheme with 21 subjects. Each subject participated in two attempts: one attempt included sound stimulation (music) and another one was sham (silence). RESULTS AND CONCLUSION: The decrease in sleep latency during stimulation is not confirmed reliably. The increase in sleep stability has been confirmed reliably using nonlinear regression model. The findings can be used in the development of non-pharmacologic ways of sleep treatment.

Changes in sleep duration associated with retirement transitions: The role of naps.

This study examined the changes in sleep duration (total sleep time, night-time sleep and daytime naps) after retirement transitions in China using a panel dataset of the China Health and Retirement Longitudinal Study in 2011, 2013 and 2015 with a total of 48,458 respondents. Linear regression analysis with generalized estimating equations was employed to examine the changes in sleep duration after transitions between different types of employment status. After controlling for the confounders, the results showed that the retired population and the population working in agricultural sectors slept 8.02 (p < .01) and 5.19 (p < .01) minutes longer than the population working in non-agricultural sectors, respectively. Employment transition also had significant effects on sleep duration. Transition from non-agricultural sectors to retirement increased total sleep time by 13.58 (p < .01) minutes and also raised the probability of daytime naps by 18% (OR = 1.18, p < .01). Transition from agricultural employment to retirement did not significantly affect the total sleep time, but significantly increased the probability of daytime naps (OR = 1.12, p = .02). Reentering the non-agricultural sectors for the retirees did not significantly affect night-time sleep, but decreased the probability of daytime naps (OR = 0.73, p < .01) and daytime nap duration (by 5.26 min, p = .01). In conclusion, people in China increased their sleep duration after transitions to retirement, but the magnitudes were much smaller than those in Western countries. Differences may be attributed to an abundant amount of Chinese people working in agricultural sectors, the high volume of retired people reentering the work force and the large proportion of people in China that had daytime naps at baseline.

Effect of music of specific frequency upon the sleep architecture and electroencephalographic pattern of individuals with delayed sleep latency: A daytime nap study.

INTRODUCTION: Sleep is normal human behaviour. However, the stress in daily life leads to altered sleep behaviour like insomnia, parasomnia, etc. Owing to possible side effects, mind-body interventions like music, yoga and meditation could be a better alternative intervention to pharmacological interventions for the condition. It is known that 432 Hz music to have some effect on the overall sleep quality though some knowledge gap does exist. The present study aims to find the effects of 432 Hz on sleep quality and sleep latency in a daytime nap among subjects with history of delayed sleep latency. MATERIAL AND METHOD: Fifteen healthy male volunteers aged 18 to 40 years with history of delayed sleep latency were recruited for the study from a cohort of working staff and students at the institute, after due ethical clearance following the inclusion and exclusion criteria. All the subjects were subjected to sleep study with and without music intervention at the gap of 1 week. Sleep parameters recorded include sleep stages, electroencephalogram (EEG), electrocardiogram (ECG), electromyography (EMG), nasal airflow, thoracic movement, nasal saturation etc. RESULT: Outcome of the study shows some decrease in the mean sleep latency (P > 0.05) with significant increase in the energy of alpha waves (P < 0.01) at the sleep onset. CONCLUSION: It was concluded that 432 Hz music has some significant calming effect as reflected by increased alpha activities without any significant effect upon the sleep latency in the daytime naps.

Exploring associations of maternal sleep during periconceptional period with congenital heart disease in offspring.

BACKGROUND: In general, the existing evidence points to a role for maternal sleep in pregnancy complications and fetal growth, however, little has been focused on birth defects. We aimed to explore the association between periconceptional poor sleep and the risk of congenital heart disease (CHD), and to examine if daytime napping could to some extent change the association. METHODS: A case-control study was conducted in Shanghai Children's Medical Center, in which, a total of 524 cases (262 simple CHD vs. 262 severe CHD), along with 262 controls. RESULTS: In the multivariable logistic analysis, poor sleep could increase the risk of both simple CHD (OR = 2.486, 95% CI = 1.619-3.818) and severe CHD (OR = 1.950, 95% CI = 1.269-2.997), while routine daytime nap could decrease risk of simple CHD (OR = 0.634, 95% CI = 0.435-0.923). In the stratified analysis, the concurrence with routine daytime nap could weaken the risk of simple CHD caused by poor sleep (OR = 3.183, 95% CI: 1.830-5.537 decreased to OR = 2.236, 95% CI: 1.200-4.165). The examinations were repeated in ventricular septal defect and tetralogy of Fallot, and the established associations can be verified. Moreover, all these findings were also similarly observed in both propensity-score-adjusted and propensity-score-matched analyses. CONCLUSIONS: Poor maternal sleep around periconceptional period seems to be an independent risk factor for CHD. The concurrence with daytime nap could to some extent reduce the risk in simple CHD. The results individually and collectively put forward the importance of maternal sleep in embryonic heart development.

Trait-like characteristics of sleep EEG power spectra in adolescents across sleep opportunity manipulations.

The electroencephalographic power spectra of non-rapid eye movement sleep in adults demonstrate trait-like consistency within participants across multiple nights, even when prior sleep deprivation is present. Here, we examined the extent to which this finding applies to adolescents who are habitually sleep restricted on school-days and sleep longer on weekends. We evaluated 78 adolescents across three sleep restriction groups who underwent different permutations of adequate sleep (9 hr time-in-bed), sleep restriction (5 hr time-in-bed), afternoon naps (1 hr afternoon) and recovery sleep (9 hr time-in-bed) that simulate behaviour on school-days and weekends. The control group comprised a further 22 adolescents who had 9 hr of sleep opportunity each night. Intra-class correlation coefficients showed moderate to almost perfect within-subject stability in electroencephalographic power spectra across multiple nights in both sleep restriction and control groups, even when changes to sleep macrostructure were observed. While nocturnal intra-class correlation metrics were lower in the low-frequency and spindle frequency bins in the sleep restriction compared with the control group, hierarchical clustering measures could still identify multi-night electroencephalographic spectra as originating from the same individual. The trait-like characteristics of electroencephalographic spectra from an adolescent remain identifiable despite the disruptive effects of multi-night sleep restriction to sleep architecture.

EEG Changes Accompanying Successive Cycles of Sleep Restriction With and Without Naps in Adolescents.

Study objectives: To investigate the temporal evolution of sleep EEG changes in adolescents across two cycles of sleep restriction and recovery simulating an intense school week and to examine the effect of an afternoon nap on nocturnal sleep. Methods: A parallel-group design, quasi-laboratory study was conducted in a student hostel. Fifty-seven adolescents (31 males, age = 15-19 years) were randomly assigned to nap or no nap groups. Participants underwent a 15-day protocol comprising two sleep restriction (5-hour time-in-bed [TIB]) and recovery (9-hour TIB) cycles. The nap group was also provided with a 1-hour nap opportunity at 14:00 following each sleep restriction night. Polysomnography recordings were obtained on nine nights and five nap episodes. Results: Naps reduced homeostatic sleep pressure on sleep restriction nights as evidenced by longer N2 latency and reduced total sleep time (TST), sleep efficiency (SE), and slow wave energy. Sleep debt accumulated in both groups, evidenced by increased TST, greater SE, and reduced wake after sleep onset on recovery compared to baseline nights. Changes were greater in the no nap group. Recovery sleep after the first cycle of sleep restriction did not restore sleep architecture to baseline in either group. SE, rapid eye movement (REM), and non-REM sleep increased, and N2 latency was reduced in the second sleep restriction period. Conclusions: Changes in sleep EEG induced by sleep restriction to 5-hour TIB for five nights were not eliminated after two nights of 9-hour recovery sleep. An afternoon nap helped but residual effects on the sleep EEG suggest that there is no substitute for adequate nocturnal sleep.

Short sleep duration and longer daytime napping are associated with non-alcoholic fatty liver disease in Chinese adults.

BACKGROUND: Epidemiologic studies have reported conflicting results on the relationship between short sleep duration and non-alcoholic fatty liver disease (NAFLD). There are no previous studies investigating the effect of daytime napping on NAFLD. In the present study we examined the associations between NAFLD and both nightly sleep duration and daytime napping in a middle-aged and elderly Chinese population. METHODS: This cross-sectional community-based population study was performed on 8559 individuals aged ≥40 years. Sleep duration and the duration of daytime napping were self-reported using a standardized questionnaire; NAFLD was diagnosed by ultrasonography. RESULTS: In this study sample, the overall prevalence of NAFLD was 30.4%. There was an inverse association between sleep duration and the risk of prevalent NAFLD. In multivariate analysis, the odds ratios (ORs) and 95% confidence intervals (CIs) of prevalent NAFLD for decreasing sleep duration categories (≥9, 8.1-9, 7.1-8, 6.1-7, and ≤6.1 h) were 1.00 (reference), 1.38 (1.13-1.70), 1.32 (1.08-1.61), 1.29 (1.04-1.60), and 1.66 (1.28-2.15), respectively (P trend = 0.0073). Compared with participants without a daytime napping habit, nap takers with a longer nap duration (>0.5 h) had an increased risk of prevalent NAFLD (OR 1.22; 95% CI 1.06-1.41). The associations of sleep duration and daytime napping duration with NAFLD were generally consistent across different categories of age and obesity, metabolic syndrome, and insulin resistance status. CONCLUSIONS: Short sleep duration and longer daytime napping were associated with an increased risk of prevalent NAFLD in a middle-aged and elderly Chinese population.

Sleep before and after learning promotes the consolidation of both neutral and emotional information regardless of REM presence.

Sleep may play a role in consolidating emotional memories. However, studies on the effects of REM sleep on negative vs. neutral memories have produced inconsistent evidence. Here, we assess the role of NREM and REM sleep before and after learning in promoting the consolidation of neutral and arousing pleasant and unpleasant memories. Forty-six (32 F) healthy university students were exposed to a set of pictures at 1:00PM (Session 1) and to an equivalent set at 4:45PM (Session 2). All the pictures in Session 1 and Session 2 were presented again, intermixed with new similar pictures at 5:15PM in a memory recognition task. Following Session 1, participants took a 90/120-min nap (NAP group), while 16 participants remained awake (WAKE group). Via polysomnographic recording, the NAP group was segregated into REM (N=14) and NoREM groups (N=16). Indices of memory consolidation for both stimuli presented before (discriminability of Session 1 pictures in Session 3) and after sleep (discriminability of Session 2 pictures in Session 3) were calculated. Memory consolidation for pictures presented both before and after the sleep period was higher in the NAP group as compared to the WAKE group, but no differential role of REM sleep emerged. A memory consolidation advantage was evident for neutral over pleasant (but not unpleasant) pictures. Taken together, these results indicate that a daytime nap (with or without REM sleep) facilitates consolidation of declarative memories presented before and after sleep irrespective of their valence.

Heart rate variability during daytime naps in healthy adults: Autonomic profile and short-term reliability.

In healthy individuals, a reduction in cardiovascular output and a shift to parasympathetic/vagal dominant activity is observed across nocturnal sleep. This cardiac autonomic profile, often measured by heart rate variability (HRV), has been associated with significant benefits for the cardiovascular system. However, little is known about the autonomic profile during daytime sleep. Here, we investigated the autonomic profile and short-term reliability of HRV during daytime naps in 66 healthy young adults. Participants took an 80-120 min polysomnographically recorded nap at 1:30 pm. Beat-by-beat RR interval values (RR), high (HF) and low frequency (LF) power, total power (TP), HF normalized units (HF(nu)), and the LF/HF ratio were obtained for 5 min during presleep wakefulness and during nap sleep stages (N2, N3, REM). A subsample of 37 participants took two additional naps with 2 weeks between recordings. We observed lengthening of the RR, higher HF and HF(nu), and lower LF/HF during NREM, compared with REM and wake, and a marked reduction of LF and TP during N3. Intraclass correlation coefficients highlighted a short-term stability of RR and HF ranging across sleep stages between 0.52-0.76 and 0.52-0.80, respectively. Our results suggest that daytime napping in healthy young adults is associated with dynamic changes in the autonomic profile, similar to those seen during nocturnal sleep. Moreover, a reliable intraindividual measure of autonomic cardiac activity can be obtained by just a single daytime nap depending on specific parameters and recording purposes. Nap methodology may be a new and promising tool to explore sleep-dependent, autonomic fluctuations in healthy and at-risk populations.