Individual and joint associations between sleep duration and physical activity with cognitive function: a longitudinal analysis among middle-aged and older adults in China

Abstract

I read the article written by Hongwei Liu and his colleagues with interest, and I would like to commend the author for conducting such a comprehensive longitudinal study, examining the relationship between sleep time, physical activity, and cognitive function among middle-aged and elderly people in China.¹ The research provides valuable insights into the potential effects of lifestyle factors, specifically sleep and physical activity, on cognitive aging. However, I would like to offer several suggestions and comments for consideration.

First, although the study considered sleep duration, it did not delve into the impact of sleep quality.^{2, 3} Research has shown that sleep quality has a significant impact on cognitive function, and analyzing solely based on sleep duration may overlook other important factors that affect cognitive function, such as sleep interruption, lack of deep sleep, etc., which may have an impact on cognition and, thus, affect the accuracy of research results.⁴

Although this study employed lagged time series models to examine causal relationships, the possibility of reverse causation cannot be completely ruled out, particularly since early-stage cognitive decline may influence both sleep patterns and physical activity levels.⁵ Specifically, deteriorating cognitive function could alter individuals' sleep habits and physical activity behaviors, making it challenging to fully disentangle the direction of causality. Future research should implement methodological approaches that minimize the potential impact of reverse causation to ensure greater validity of findings.^6-8

While this study thoroughly examined the relationships between sleep and physical activity, it may not have adequately addressed the potential non-linear effects of these variables. For instance, moderate physical activity might enhance cognitive function, whereas excessive physical activity could potentially yield adverse effects.⁹ The analyses conducted in this study may not have fully captured such non-linear relationships. Furthermore, the lack of detailed categorization of physical activity types and intensities represents another limitation, as different forms of exercise (such as aerobic exercise and strength training) may differentially impact cognitive function, potentially affecting the precision of our findings.¹⁰

Based on our findings, we propose implementing a three-tiered response system for cognitive health management. The first tier focuses on broad public health education, promoting awareness of cognitive health through campaigns that emphasize the importance of proper sleep habits and appropriate physical activity levels. The second tier targets high-risk populations, such as elderly individuals and those with family history of cognitive decline, providing tailored sleep management protocols and exercise guidance, along with regular cognitive assessments and early warning monitoring. The third tier addresses individuals already experiencing cognitive impairment, offering specialized medical interventions and rehabilitation services, including personalized exercise prescriptions, sleep therapy, and other supportive measures, while also providing essential guidance and support for their caregivers. This stratified approach ensures comprehensive coverage from prevention to intervention, optimizing resource allocation and utilization efficiency.

In summary, this study presents important findings and makes a significant contribution to our understanding of lifestyle factors that affect cognitive aging. Meanwhile, constructing a three-level response system for cognitive intervention provides an effective way to delay cognitive decline. I believe that further research on the above suggestions will enrich our knowledge in this field and provide more precise guidance for interventions aimed at promoting cognitive health in the elderly.

The author declares no conflicts of interest. Author disclosures are available in the supporting information.