Triglycerides, high-density lipoprotein and cognitive function in middle-aged and older adults: a cross-sectional analysis.

As China's population continues to age, addressing cognitive decline related to aging has become increasingly important. Simultaneously, rapid economic development has led to rising concerns about lipid metabolism disorders, particularly those involving blood lipids. Identifying modifiable risk factors early is critical to enhancing cognitive function in older adults. Thus, this study focuses on the relationship between triglycerides (TG), high-density lipoprotein (HDL), and cognitive performance to investigate potential mechanisms. A cross-sectional study was conducted using data from the 2015 China Health and Retirement Longitudinal Study (CHARLS) survey. Cognitive function was assessed across three domains: global cognition, episodic memory, and mental status. Fasting blood samples were analyzed for triglycerides and high-density lipoprotein (HDL) levels. The relationship between triglycerides, HDL, and cognitive function was examined using restricted cubic spline (RCS) analysis, multivariate linear regression, and mediation analysis. The analysis identifies a non-linear, inverse U-shaped relationship between triglycerides and both global cognition and episodic memory, with significant inflection points at a triglyceride (TG) level of 202.65 for global cognition and 115.04 for episodic memory. No non-linear relationship was observed between High-Density Lipoprotein (HDL) and cognitive outcomes, including global cognition, episodic memory, or mental status (p > 0.05). Linear mixed models indicate that HDL has a positive association with episodic memory, as shown by HDLQ1 (B = 0.0033, 95% CI: 0, 0.569), HDLQ2 (B = 0.039, 95% CI: 0.051, 0.594), and HDLQ3 (B = 0.033, 95% CI: 0.004, 0.556) compared to HDLQ4. A combined analysis of TG and HDL on episodic memory further demonstrated that the ''High-TG-low-HDL'' group (B = 0.036, 95% CI: 0.043, 0.578) had a significantly positive effect compared to the "High-HDL-low-TG" group. Mediation analysis revealed that Body Mass Index (BMI) indirectly mediated the HDL-episodic memory relationship, with a mediation effect size of 22.2%. In conclusion, this study explored the interplay between triglyceride levels, high-density lipoprotein cholesterol (HDL-C) levels, and cognitive function among middle-aged and elderly individuals in China. The findings reveal a U-shaped inverse relationship between triglyceride concentrations and cognitive ability, underscoring the need to maintain optimal triglyceride levels for cognitive health. Additionally, lower HDL levels (HDLQ1-Q3) were found to positively affect cognitive function, particularly in overall cognition and episodic memory, compared to higher HDL levels (HDLQ4). Importantly, body mass index (BMI) mediated the influence of HDL on episodic memory, with an effect size of 22.2%.