Association between Obesity and Cognitive Function in Chinese Older Adults: The Mediating Effects of Sleep Quality and Blood Pressure.

Introduction: The mechanisms underlying the relationship between obesity and cognitive function remain unclear, particularly among older adults, where reliable evidence is limited. This study aimed to explore whether the relationship between obesity and cognitive function is mediated by sleep quality and blood pressure (BP) in older Chinese adults.

Methods: We conducted an observational study using data from a cluster randomized controlled trial (RCT) with 5 follow-up periods involving older adults in rural China. The trial took place in Sichuan, China, from May 2021 to May 2023. Telephone Interview for Cognitive Status (TICS- 10) was used to assess the participants' cognitive function. Additionally, linear mixed-effects models and mediation analyses were performed.

Results: The mean age of participants was 70.89, and 225 out of 506 participants were males. Weight, waist circumference (WC), and hip circumference (HC) were positively associated with cognitive function, while compared to normal/underweight participants, participants with overweight had a significant association with cognitive function. Sleep quality mediated the association between weight and cognitive function (β = 0.01, [95% CI: 0.00 to 0.01], P < 0.001), accounting for a mediating effect proportion of 4.04% [95% CI: 2.19% to 8.00%]. Diastolic blood pressure (DBP) mediated the association between overweight (β = 0.02, [95% CI: 0.00 to 0.05], P < 0.001), HC (β = 0.01, [95% CI: 0.00 to 0.01], P = 0.02), and WC (β = 0.01, [95% CI: 0.00, 0.01], P <0.001) and cognitive function, explaining approximately 4.46% (95% CI: 0.41% to 12.00%), 7.16% (95% CI: 0.36%, 17.00%), and 9.60% (95% CI: 1.11%, 25.00%) mediating proportion of the total effect, respectively.

Discussion: Our study highlights the potential mediating roles of sleep quality and DBP in the relationship between obesity and cognitive function. The findings contribute to understanding the obesity-cognition link in older adults, particularly in rural settings. However, limitations, such as self-reported sleep measures and unmeasured confounders, warrant caution. Further research is needed to clarify the underlying mechanisms and inform targeted interventions.

Conclusion: Our study demonstrates a significant positive association between weight, body mass index (BMI), HC, and WC and cognitive function in older adults. These findings suggest that maintaining a moderately high level of adiposity may be protective against cognitive decline in this population. Additionally, the study also provides insights into optimizing cognitive function through factors, such as sleep and BP management.