Daytime sleep accelerates cardiovascular recovery after psychological stress

Longitudinal associations between daytime napping and cognitive function in Chinese older adults

BACKGROUND

Little was known about the longitudinal associations between daytime napping and cognitive function in China. Thus, the study aimed to explore the cross-sectional and the longitudinal relationship between daytime napping and cognitive performance in the elderly Chinese population.

METHODS

The data was from the China Health and Retirement Longitudinal Study (CHARLS). Daytime napping was self-reported. Cognitive function was assessed via a structured questionnaire in two dimensions: episodic memory and mental status. Linear regression and mixed-effect model were applied to explore the association between daytime napping and cognitive function.

RESULTS

A total of 2,875 and 2,440 participants aged over 65 years were included in the cross-sectional and the longitudinal studies, respectively. In the cross-sectional study, non-nappers and extended nappers had significantly lower global cognition scores (P<0.01), as well as significantly lower scores for episodic memory (P<0.05) and mental status (P<0.01), compared with moderate nappers. In the longitudinal analysis, no napping and extended napping were significantly associated with global cognitive decline (P<0.05) and only extended napping showed the significant association for the decline in episodic memory as well as mental status (P<0.01).

LIMITATIONS

Daytime napping duration was self-reported by participants.

CONCLUSION

The study found a longitudinal association between extended napping duration and worse cognitive function.

Separating the influences of means and daily variations of sleep on the stress-induced salivary cortisol response

BACKGROUND

Previous research regarding the effects of sleep quality and quantity on the acute stress response has yielded inconsistent findings. This may be attributed to various factors, including composite sleep components (i.e., means and daily variations) and mixed cortisol stress response (i.e., reactivity and recovery). Thus, this study aimed to separate the effects of means and daily variations of sleep on the reactivity and recovery of cortisol responses to psychological challenges.

METHODS

In study 1, we recruited 41 healthy participants (24 women; age range, 18-23 years), monitored their sleep during seven consecutive days via wrist actigraphy and sleep diaries, and adopted the Trier Social Stress Test (TSST) paradigm to induce acute stress. Study 2 consisted of a validation experiment using the ScanSTRESS paradigm, which included 77 additional healthy individuals (35 women; age range, 18-26 years). Similarly to the TSST, the ScanSTRESS induces acute stress using uncontrollability and social evaluation. In both studies, saliva samples from the participants were collected before, during, and after the acute stress task.

RESULTS

Using residual dynamic structural equation modeling, both study 1 and study 2 demonstrated that higher means of objective sleep efficiency, and longer means of objective sleep duration were related to greater cortisol recovery. In addition, fewer daily variations in objective sleep duration were associated with greater cortisol recovery. However, there was no correlation between sleep variables and cortisol reactivity, except for the daily variations in objective sleep duration in study 2. No correlation was observed between subjective sleep and cortisol response to stress.

CONCLUSIONS

The present study separated two features of multi-day sleep patterns and two components of cortisol stress response, providing a more comprehensive picture of the effect of sleep on the stress-induced salivary cortisol response, and contributing to the future development of targeted interventions for stress-related disorders.

Self-reported sleep in relation to risk of dementia a quarter of a century later at age 90+: The 90+ Study

OBJECTIVE

To examine sex-specific associations of sleep duration and napping self-reported at mean age of 69 years (range: 53-81) with risk of incident dementia 24 years later at age 90 +.

METHOD

Analytic sample included individuals from a population-based study who reported sleep and napping once in the 1980s and 24 years later (range: 16-38) joined The 90+ Study and were evaluated in-person. Those without dementia at baseline of The 90+ Study were prospectively followed. Hazard ratios [HR] and 95% confidence intervals [CI] of dementia risk were estimated by Cox regression.

RESULTS

Of 574 participants 71% were women, mean age at start of dementia follow-up with The 90+ Study was 93 years (range: 90-102). After 3.3 years (range: 0.4-13.8) of follow-up 47% developed dementia. Higher risk of dementia at age 90+ was seen in women with <6 hours of self-reported sleep per night (adjusted HR = 2.00; 95% CI = 1.15-3.50; p = .01) compared with 8 hours. Lower risk of dementia at 90+ was seen in men with short-to-moderate (<60 minutes) self-reported naps compared with no naps (HR = 0.33; 95% CI = 0.18-0.63; p < .01).

CONCLUSIONS

Sleep and nap 24 years earlier are important risk factors for dementia after age 90.

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 association of nighttime sleep duration and daytime napping duration with hypertension in Chinese rural areas: a population-based study

We aimed to investigate the association of self-reported nighttime sleep duration and daytime napping duration with hypertension in rural areas of China. The participants, who were from rural areas of Hunan Province in China, were enrolled during 2016-2017. Nighttime sleep duration (<7 h, 7-8 h, and ≥9 h) and daytime napping duration(no nap, 0-1 h, and >1 h) were determined by a self-reported questionnaire. Hypertension was defined as a mean systolic blood pressure ≥140 mmHg and/or a mean diastolic blood pressure ≥90 mmHg or a self-reported physician diagnosis of hypertension and current use of antihypertensive medication. Of 1763 enrolled participants, 52% had hypertension. A total of 640 (36%) were male and 1123 (64%) were female; the mean age was 56 years. After adjusting for potential confounders, participants who slept for ≥9 h per night had a 1.29-fold (95% CI: 1.03, 1.60) increased odds of hypertension compared to the reference group (7-8 h per night). Daytime napping >1 h was negatively associated with hypertension, with an adjusted OR (95% CI) of 0.70 (0.51, 0.97), and the protective effect of longer daytime napping was still found in the subgroup sleeping 7-8 h per night. Among the rural population in China, long nighttime sleep duration is associated with a higher prevalence of hypertension, and longer daytime napping is related to a decreased prevalence of hypertension.

Effect of an Inflatable Air Mattress with Variable Rigidity on Sleep Quality

Several studies, wherein the structure or rigidity of a mattress was varied, have been conducted to improve sleep quality. These studies investigated the effect of variation in the surface characteristics of mattresses on sleep quality. The present study developed a mattress whose rigidity can be varied by controlling the amount of air in its air cells. To investigate the effect of the variable rigidity of the air mattress on sleep quality, participants (Male, Age: 23.9 ± 2.74, BMI: 23.3 ± 1.60) were instructed to sleep on the air mattress under different conditions, and their sleep quality was subjectively and objectively investigated. Subjectively, sleep quality is assessed based on the participants’ evaluations of the depth and length of their sleep. Objectively, sleep is estimated using the sleep stage information obtained by analysing the movements and brain waves of the participants during their sleep. A subjective assessment of the sleep quality demonstrates that the participants’ sleep was worse with the adjustment of the air mattress than that without; however, the objective sleep quality results demonstrates an improvement in the sleep quality when the rigidity of the air mattress is varied based on the participant’s preference. This paper proposes a design for mattresses that can result in more efficient sleep than that provided by traditional mattresses.

Effects of Social Exclusion on Cardiovascular and Affective Reactivity to a Socially Evaluative Stressor

PURPOSE

Socially disconnected individuals have worse health than those who feel socially connected. The mechanisms through which social disconnection influences physiological and psychological outcomes warrant study. The current study tested whether experimental manipulations of social exclusion, relative to inclusion, influenced subsequent cardiovascular (CV) and affective reactivity to socially evaluative stress.

METHODS

Young adults (N = 81) were assigned through block randomization to experience either social exclusion or inclusion, using a standardized computer-based task (Cyberball). Immediately after exposure to Cyberball, participants either underwent a socially evaluative stressor or an active control task, based on block randomization. Physiological activity (systolic blood pressure (SBP), diastolic blood pressure (DBP), heart rate (HR)) and state anxiety were assessed throughout the experiment.

RESULTS

Excluded participants evidenced a significant increase in cardiovascular and affective responses to a socially evaluative stressor. Included participants who underwent the stressor evidenced similar increases in anxiety, but systolic blood pressure, diastolic blood pressure, and heart rate did not change significantly in response to the stressor.

CONCLUSIONS

Results contribute to the understanding of physiological consequences of social exclusion. Further investigation is needed to test whether social inclusion can buffer CV stress reactivity, which would carry implications for how positive social factors may protect against the harmful effects of stress.

The Concept of Qailulah (Midday Napping) from Neuroscientific and Islamic Perspectives

Napping/siesta during the day is a phenomenon, which is widely practised in the world. However, the timing, frequency, and duration may vary. The basis of napping is also diverse, but it is mainly done for improvement in alertness and general well-being. Neuroscience reveals that midday napping improves memory, enhances alertness, boosts wakefulness and performance, and recovers certain qualities of lost night sleep. Interestingly, Islam, the religion of the Muslims, advocates midday napping primarily because it was a practice preferred by Prophet Muhammad (pbuh). The objectives of this review were to investigate and compare identical key points on focused topic from both neuroscientific and Islamic perspectives and make recommendations for future researches.

The Siesta Habit is Associated with a Decreased Risk of Rupture of Intracranial Aneurysms

BACKGROUND

Previous studies have examined an association between the siesta habit and hypertension, as well as coronary heart disease. However, the relationship between a siesta and the risk of rupture of an intracranial aneurysm (IA) has not yet been established. We aimed to investigate the effects of a siesta on the risk of rupture of IAs.

METHODS

We prospectively enrolled consecutive patients diagnosed with IAs at our hospital between January 2016 and December 2016. Univariate and multivariate logistic regression analysis were performed to identify independent risk factors associated with IA rupture.

RESULTS

We studied 581 consecutive patients with 514 unruptured and 120 ruptured aneurysms. Univariate analysis demonstrated that hypertension, hyperlipidemia, diabetes mellitus, cigarette smoking, location, size, as well as shape and aspect ratio were associated with the risk of rupture of IAs. Multivariate analysis identified hypertension [odds ratio (OR) 1.68, 95% confidence interval (CI) 1.03-2.73], hyperlipidemia (OR 0.25, 95% CI 0.08-0.72), current cigarette smoking ≥20 cigarettes/day (d) (OR 3.48, 95% CI 1.63-7.47), siesta (siesta time <1 h, OR 0.49, 95% CI 0.24-0.98 and siesta time ≥1 h, OR 0.32, 95% CI 0.19-0.57), location of largest aneurysm on the anterior communicating and internal carotid-posterior communicating artery (PCOM) (anterior communicating artery OR 16.27, 95% CI 7.40-35.79 and PCOM OR 11.21, 95% CI 5.15-24.43), and size of aneurysm ≥7 mm (OR 2.19, 95% CI 1.21-3.97) as independent strong risk factors associated with risk of aneurysm rupture.

CONCLUSION

In the present study, we found that a habitual siesta is a new predictive factor to assess the risk of rupture of an IA. We found the siesta habit may reduce the risk of aneurysm rupture. We also found that hypertension, hyperlipidemia, cigarette smoking, location, and size of aneurysm were associated with the risk of rupture of IAs.

Sleep Duration and Quality in Relation to Autonomic Nervous System Measures: The Multi-Ethnic Study of Atherosclerosis (MESA)

STUDY OBJECTIVES

Short sleep duration and poor sleep quality are associated with adverse cardiovascular outcomes. Potential pathophysiological mechanisms include sleep-associated alterations in the autonomic nervous system. The objective of this study was to examine the associations of shorter sleep duration and poorer sleep quality with markers of autonomic tone: heart rate (HR), high-frequency HR variability (HF-HRV) and salivary amylase.

METHODS

Cross-sectional analysis of data from actigraphy-based measures of sleep duration and efficiency and responses to a challenge protocol obtained from 527 adult participants in the Multi-Ethnic Study of Atherosclerosis.

RESULTS

Participants who slept fewer than 6 h per night (compared to those who slept 7 h or more per night) had higher baseline HR (fully adjusted model 0.05 log beats/min, 95% confidence interval [CI] 0.01, 0.09) and greater HR orthostatic reactivity (fully adjusted model 0.02 log beats/min, 95% CI 0.002, 0.023). Participants who slept 6 to less than 7 h/night (compared to those who slept 7 h or more per night) had lower baseline HF-HRV (fully adjusted model -0.31 log msec², 95% CI -0.60, -0.14). Participants with low sleep efficiency had lower baseline HF-HRV than those with higher sleep efficiency (fully adjusted model -0.59 log msec², 95% CI -1.03, -0.15). Participants with low sleep efficiency had higher baseline levels of amylase than those with higher sleep efficiency (fully adjusted model 0.45 log U/mL, 95% CI 0.04, 0.86).

CONCLUSIONS

Short sleep duration, low sleep efficiency, and insomnia combined with short sleep duration were associated with markers of autonomic tone that indicate lower levels of cardiac parasympathetic (vagal) tone and/or higher levels of sympathetic tone.

Clinical Implications of Impaired Sleep

Despite its pervasiveness in primary care, deficient sleep often is underappreciated as a cue to other health risks. Accordingly, this review discusses contemporary evidence-based perspectives on impaired sleep and its associations with other lifestyle medicine concerns, including obesity, cardiovascular conditions, psychological problems, and health-compromising habits. The potential clinical benefits of promoting sleep health also will be considered.

Sleep duration and cardiovascular responses to stress in undergraduate men

Short sleep has been related to incident cardiovascular disease, but physiological mechanisms accounting for this relationship are largely unknown. This study examines sleep duration and cardiovascular stress responses in 79 healthy, young men. Sleep duration was assessed by wrist actigraphy for seven nights. Participants then completed a series of laboratory stress tasks while heart rate and blood pressure were monitored. Shorter total sleep time was related to a greater reduction in high-frequency heart rate variability during stress tasks, and to prolonged elevations in heart rate and diastolic pressure following tasks. Associations were independent of age, race, body mass index, caffeine intake, and smoking status. In sum, healthy young men with shorter actigraphy-assessed sleep exhibit less cardiac vagal activity, and poorer heart rate and diastolic blood pressure recovery, upon encountering stressful stimuli, than those with longer sleep.

Sleep from an Islamic perspective

Sleep medicine is a relatively new scientific specialty. Sleep is an important topic in Islamic literature, and the Quran and Hadith discuss types of sleep, the importance of sleep, and good sleep practices. Islam considers sleep as one of the signs of the greatness of Allνh (God) and encourages followers to explore this important sign. The Quran describes different types of sleep, and these correspond with sleep stages identified by modern science. The Quran discusses the beneficial effects of sleep and emphasizes the importance of maintaining a pattern of light and darkness. A mid-day nap is an important practice for Muslims, and the Prophet Muhammad peace be upon him (pbuh) promoted naps as beneficial. In accordance with the practice and instructions of Muhammad (pbuh), Muslims have certain sleep habits and these sleep habits correspond to some of the sleep hygiene rules identified by modern science. Details during sleep include sleep position, like encouraging sleep on the right side and discouraging sleep in the prone position. Dream interpretation is an established science in the Islamic literature and Islamic scholars have made significant contributions to theories of dream interpretation. We suggest that sleep scientists examine religious literature in general and Islamic literature in particular, to understand the views, behaviors, and practices of ancient people about the sleep and sleep disorders. Such studies may help to answer some unresolved questions in sleep science or lead to new areas of inquiry.

Qur'anic insights into sleep

Sleep has preoccupied and fascinated many civilizations since the dawn of mankind. Here, we critically review the various elements pertaining to sleep in the context of early Islamic religion and culture. The many principles of sleep hygiene, wellbeing and health associated with adequate sleep, and the understanding of sleep as a dynamic state are all apparent from such explorative process of Islamic tradition.