This study investigated the associations between sleep duration and cognitive performance in older adults. The study found that long sleep may be related to the decline of cognitive function in the elderly, and participants who slept moderately (7–9 hours per night) performed better on cognitive tests, with higher CERAD, AFT, and DSST scores.
Previous research has extensively explored the relationship between sleep duration and cognitive performance. Zijlmans J et al.[14] conducted a population-based study, suggesting longer sleep onset latency is mainly associated with lower cognitive reserve; Wang et al.[9] found that sleep duration was significantly negatively correlated with cognitive performance. A study published by Li et al. [24] from Fudan University in the Nature sub-journal found that the optimal length of sleep was 7 hours, which was positively associated with cognitive function and mental health. However, when sleep was insufficient or more than 7 hours, it was associated with cognitive decline and poor mental health[24]. Through the European Longitudinal cohort study on the Prevention of Alzheimer's dementia (EDPA-LAC), Blackman et al. [25] found that sleep of fewer than 7 hours was associated with an increased pathological burden of Alzheimer's disease in people without cognitive impairment.
Compared to these previous studies, our research delves deeper into the association between sleep duration and cognitive performance among the elderly. While prior research has provided valuable insights into this relationship, our study offers several novel contributions. Firstly, we utilized data from the National Health and Nutrition Survey from 2011 to 2014, encompassing a large and diverse sample of participants. This allows for a robust analysis of the relationship between sleep duration and cognitive function. Secondly, our study employed a weighted multivariate logistic regression model, adjusting for various covariates to minimize confounding effects. Furthermore, we utilized a restricted cubic spline model to explore the nonlinear relationship between sleep duration and cognitive performance, providing a more nuanced understanding of this association.
Despite these advancements, our study shares some similarities with prior research. Like previous studies, we found a significant positive correlation between prolonged sleep duration (more than 9 hours per night) and cognitive decline. This aligns with the findings of Zijlmans J et al. [14] and Wang et al. [9], highlighting the detrimental effects of excessive sleep on cognitive health in the elderly. However, unlike previous studies, we did not observe a significant correlation between short sleep duration (less than seven hours per night) and cognitive function. Instead, participants who slept moderately (7–9 hours per night) demonstrated better cognitive performance across various tests, consistent with the findings of Li et al. [24] and Blackman et al. [25].
In summary, while our study builds upon prior research, offering novel insights into the relationship between sleep duration and cognitive performance in the elderly, it also reinforces some existing findings. By leveraging a robust methodology and a large dataset, our study contributes to a deeper understanding of this crucial association with implications for cognitive health interventions in aging populations.
Our results clearly show that sleep duration is highly correlated with cognitive functioning. Long sleep may be related to the decline of cognitive function in the elderly, particularly in the CERAD and Animal Fluency tests. This association may reflect the effect of sleep on cognitive processes in the brain. However, the association with DSST testing is weak, and more in-depth research may be needed to explain the mechanisms behind it. We believe that the following three mechanisms could explain the current findings. First, long-term sleep may have adverse effects on cognitive function through a variety of physiological pathways. One of them may involve the regulation of the biological clock[26]. An extended sleep period may disrupt the normal circadian rhythm, resulting in abnormal levels of neurotransmitters in the brain during a specific period, thus affecting cognitive functions such as memory and language[27–29]. Second, the effect of sleep on brain neurotransmitters excessive sleep may lead to disorders in the level of neurotransmitters in the brain, especially those closely related to cognitive function, such as acetylcholine[30]. This may hinder the everyday communication of nerve cells and eventually affect the execution of cognitive function. Third, the relationship between sleep duration and brain structure. Long sleep may be related to changes in brain structure[31]. Previous studies have shown that long periods of sleep may reduce the volume of gray matter, especially in brain regions associated with cognitive function[32]. This may be one of the potential mechanisms for the correlation between sleep duration and cognitive function. Finally, although we focused on the differences in long sleep in different groups of people with diabetes, our results showed no significant correlation between sleep duration and cognitive function in this group. This may be related to the effect of diabetes on cognitive function and the intervention of other factors[33]. Future research can dig deeper into this relationship.
There are some limitations in our study. First, the data used in our study came from cross-sectional surveys, which limited the establishment of causality. Longitudinal studies are more suitable to clarify the temporal sequence and causal direction between sleep duration and cognitive function. Secondly, the assessment of sleep duration depends on self-reported data, which is affected by recall bias and inaccuracy. Objective sleep measurement methods, such as behavioral recorders or polysomnograms, can provide more reliable sleep duration and quality data. Thirdly, although we have adjusted various confounding factors in the analysis, there may still be residual confounding factors that have not been considered. Sleep disorders, drug use, and environmental factors may affect sleep duration and cognitive function, but our analysis does not include them. Fourthly, our research focuses on the elderly, and the results may not apply to young people or individuals with specific health conditions. Future studies should explore the relationship between sleep duration and cognitive function in different age groups and clinical populations.
Furthermore, the cognitive performance tests used in our study may not comprehensively capture all aspects of cognitive functioning. Including a broader range of cognitive assessments may provide a more nuanced understanding of the relationship between sleep duration and cognitive performance. Furthermore, our study did not explore the mechanisms underlying the observed associations. Future studies should explore biological, neuroimaging, and molecular pathways to elucidate potential mechanisms between sleep duration and cognitive function in older adults. Finally, as with any observational study, unmeasured confounding factors and deviations may affect the results. Caution should be taken in interpreting the findings, and further research is needed to confirm our observations and address these limitations.