Threshold effects of sleep duration and cognitive function in older adults with BMI ≥ 25 kg/m2.

Background: It has been demonstrated that older adults' cognitive capacities can be improved with sleep duration. However, the relationship between overweight, obesity, and cognitive decline remains a subject of debate. The impact of sleep duration on cognitive performance in seniors with a body mass index (BMI) ≥ 25 kg/m² is largely unknown. This makes it an intriguing subject to explore further.

Methods: This study used data from the National Health and Nutrition Examination Survey (NHANES) (2011-2014) with 2,243 participants. Weighted multivariate linear regression and smooth curve fitting were employed to investigate linear and non-linear relationships. A two-part linear regression model was used to determine the threshold effects. Additionally, subgroup analysis and interaction tests were conducted.

Results: Results showed that a negative association was found between sleep duration and scores in the fully adjusted model in the Consortium to Establish a Registry for Alzheimer's Disease (CERAD) test, the Animal Fluency test (AFT), and the Digit Symbol Substitution test (DSST). A two-piecewise linear regression model was then applied to explore the threshold effect of sleep duration on cognitive performance. When sleep duration was less than 5 and 6 h per day, sleep duration was positively correlated with CERAD test scores [ß (95% CI): 2.11 (1.17, 3.05), p < 0.0001], AFT scores [β (95% CI): 0.25 (-0.17, 0.67), p = 0.2376], and DSST scores [ß (95% CI): 0.49 (-0.57, 1.56), p = 0.3654]. However, there was a threshold effect where sleep duration reached the three inflection points.

Conclusion: In overweight and obese older adults, there is a clear inverted U-shaped relationship between sleep duration and cognitive function, with consistent results across different subgroups. Sleep durations of around 5-6 h may help prevent cognitive decline in older adults with a BMI ≥ 25 kg/m².