Obesity as a protective factor for cognitive function: a longitudinal study in a middle-aged and older Chinese adults

Background Overweight and obesity may reduce the incidence of dementia and mortality among older adults. We investigated this phenomenon in a seven-year longitudinal study. Methods We included 18,808 individuals (aged 45 + years) in four waves from 2011 to 2018 who were not diagnosed with dementia (mean [SD] age: 61.87 [8.88] years). We measured their body mass index (BMI) as a continuous value and categorized them into underweight (< 18.5), normal weight (18.5–23.9), overweight (24.0-27.9), and obesity (≥ 28.0) categories. We assessed cognitive function via the Telephone Interview for Cognitive Status (TICS), immediate recall, delayed recall, visuospatial abilities, and global cognition. We examined the association between BMI and cognitive function using a fixed model with lagged independent variables from prior study waves. Results This investigation reveals an inverted U-shaped association between BMI values and cognitive function. First, compared to normal-weight individuals, we found a statistically significantly negative association between underweight and overall cognition (ß = -0.644; 95% CI: -1.318-0.031), while overweight (ß = 0.501; 95% CI:0.079–0.924) and obesity (ß = 0.698; 95% CI :0.064–1.333) were statistically significantly associated with higher cognitive scores. Second, we identified an optimal BMI of 33.4 kg/m ² using the global cognition index. Third, social participation and physical exercise are vital in increasing cognitive function. Finally, a heterogeneity analysis found that male and urban cohorts experience more pronounced cognitive benefits with an increasing BMI. Conclusion Mild obesity was associated with improved cognitive function in a middle-aged and older Chinese population.