Association Between Nap and Reported Cognitive Function and Role of Sleep Debt: A Population-Based Study

Benefits of napping habits in healthy adults: Maintaining alerting performance and cortisol levels change within 90 min of habitual napping time

BACKGROUND

Napping is garnering increased attention as a strategy for adults to sustain alertness and alleviate stress in contemporary society. The nuances of napping habits are emerging as an independent factor influencing the extent of individual benefits. This study aimed to demonstrate the long-term benefits of napping and explore the impact of napping habits on individual alertness, as well as whether this effect was correlated with cortisol levels.

METHODS

The study involved 80 healthy adults categorized into two groups based on self-reported napping habits: habitual nappers (n = 49) and non-habitual nappers (n = 31). Karolinska Sleepiness Scale (KSS), psychomotor vigilance task (PVT), and saliva collection were performed every 30 min within 90 min in the absence of napping during the afternoon dip. The measurements were analyzed using repeated measures ANOVA and Pearson correlation analyses.

RESULTS

There was an interaction between groups and time in reaction speed and lapse number of PVT and cortisol (all p < 0.05). Post hoc analysis found that habitual nappers maintained higher objective alertness and experienced more significant increases in cortisol over time (all p < 0.05). The cortisol levels at sleepiness time were negatively associated with the slowest 10 % reaction speed of PVT in non-habitual nappers (r = -0.409, p = 0.022).

CONCLUSION

Under the premise of mitigating the impacts of acute nap deprivation on sleep homeostasis and rhythm, napping habits emerge as a potential factor influencing the ability of individuals to sustain heightened alertness.

Lifestyle Influence on Mild Cognitive Impairment Progression: A Decision Tree Prediction Model Study

Purpose

This study assessed the influences of different lifestyle on mild cognitive impairment (MCI) progression and established a decision tree prediction model to analyse their predictive significance on MCI progression incidence.

Patients and Methods

From October 2015 to February 2020,330 patients with MCI were recruited, and demographic and lifestyle information collected. They were followed up for 19.04 ± 10.227 months. Cognitive function was assessed using the Mini-Mental State Examination Scale every 6 months, and they were divided into MCI stable group and MCI progression group.

Results

The Kaplan Meier survival analysis showed an overall cohort survival rate of 33.2%; the annual conversion rate of MCI progression was 20%. Physical exercise, social engagement, high-fat diet, age, napping, and tea drinking were decision tree prediction model nodes. Hobbies were the most important factor for predicting MCI progression. The MCI progression probability rates were: with hobbies 26.829% (44 cases), without hobbies 57.831% (96 cases); for those withot hobbies, with physical exercise 43.077% (28 cases) without physical exercise 72.340% (68 cases); for those without hobbies with physical exercise and social engagement 20.000% (4 cases), without social engagement 53.333% (24 cases); for those without hobbies, physical exercises and social engagement and with nap habits 48.485% (16 cases), without nap habits 66.667% (8 cases). The decision tree prediction model AUC for predicting the MCI progression receiver operating characteristic curve was 0.737 (95% confidence interval: 0.685-0.785) (75.71% sensitivity, 71.75% specificity, P < 0.001.

Conclusion

Hobbies, physical exercise, social engagement, napping, and drinking tea can help prevent MCI progression, while a high-fat diet may exacerbate MCI progression. In this study the rule with the lowest MCI progress probability for those who had hobbies, high-fat diet, and social engagement. And the decision tree model had good prediction efficiency.

Can afternoon napping protect against the negative effect of short or long sleep duration on cognitive function? A prospective study

OBJECTIVES

Afternoon napping has been found to be able to compensate for the negative health effects of less optimal nighttime sleep duration. Our study aimed to investigate whether napping can protect against the negative effects of short or long sleep duration on cognitive function among middle-aged and older adults.

METHODS

A total of 8107 participants (men, 53.19%) aged 45 and older from the China Health and Retirement Longitudinal Study were followed prospectively for 7 years. The primary outcome was cognitive function (episodic memory and mental status). Afternoon napping was categorized into three groups including non- (0 min), moderate (1-30 min) and long (>30 min) duration. Nighttime sleep was also categorized into three groups including short (<7 h), normal (7-8 h), and long (>8 h) duration. Linear mixed models were used with napping and sleep duration at baseline as predictors. Potential confounders including baseline cognitive function were adjusted.

RESULTS

Shorter sleep duration (B = -0.01, p = 0.048) was independently associated with a faster decline in episodic memory. For participants with shorter sleep duration, either non-napping (B = -0.03, p = 0.017) or longer napping (B = -0.04, p = 0.018) showed a significant decline of episodic memory. For participants with longer sleep duration, non-napping was associated with a significant decline of episodic memory (B = -0.07, p = 0.003).

CONCLUSIONS

This study found that moderate napping could protect against the negative effects of short or long sleep duration on episodic memory, which implied that middle-aged and older adults who have a less optimal sleep duration might benefit from moderate napping for their cognitive function.

Evaluating the Bidirectional Causal Association Between Daytime Napping and Alzheimer’s Disease Using Mendelian Randomization

Background: Until now, both cross-sectional and longitudinal studies have identified controversial findings about the association between daytime napping and Alzheimer’s disease (AD) or cognitive decline. Therefore, it remains unclear about the causal association between daytime napping and AD or cognitive decline. Objective: We aim to investigate the causal association between daytime napping and AD. Methods: Here, we conduct a bidirectional Mendelian randomization (MR) analysis to investigate the causal association between daytime napping and AD using large-scale GWAS datasets from daytime napping including 452,633 individuals of European ancestry and AD including 35,274 AD and 59,163 controls of European ancestry. A total of five MR methods are selected including inverse-variance weighted (IVW), weighted median, MR-Egger, MR-PRESSO, and contamination mixture method. Results: MR analysis highlights significant causal association of AD with daytime napping using IVW (beta = -0.006, 95% CI [–0.009, –0.002], p = 2.00E-03), but no significant causal association of daytime napping with AD using IVW (OR = 0.76, 95% CI 0.53-1.10, p = 1.40E-01). Conclusion: Our bidirectional MR analysis demonstrates the causal effect of AD on daytime napping. However, there is no causal effect of daytime napping on AD. Our current findings are consistent with recent evidence from other MR studies that highlight little evidence supporting a causal effect of sleep traits on AD and support the causal effect of AD on sleep traits.