Abstract: Objective To investigate the independent and joint effects of the triglyceride glucose index (TyG) and the body roundness index (BRI) on the risk of dementia in the elderly. Methods The data were obtained from the 2011 China Health and Retirement Longitudinal Study (CHARLS), and a total of 2 710 older adults without dementia at baseline were selected, who underwent questionnaire surveys and physical examinations. Participants were categorized based on the median values of TyG and/or BRI. The occurrence of dementia during the follow-up in 2018 was recorded. Logistic regression models were used to analyze the associations between TyG/BRI and dementia onset, and their additive and multiplicative interactions were further assessed. Results The mean age of the 2 710 participants was 66.5±5.5 years. During follow-up in 2018, a total of 443 incident dementia cases were identified, with an incidence rate of 16.3%. In the multivariable-adjusted models, after adjusting for age, gender, educational level, marital status, residence, body mass index, smoking, alcohol consumption, social engagement, diabetes, hypertension, cardiovascular disease, dyslipidemia, and baseline cognitive function, both high TyG (OR=1.41,95%CI:1.09-1.82) and high BRI(OR=1.68,95%CI:1.22-2.32)were associated with an increased risk of dementia. Compared to the low TyG/low BRI group, the group with high TyG and high BRI had the highest risk of dementia (OR=2.28,95%CI:1.53-3.41). No significant additive or multiplicative interaction was found between TyG and BRI. Subgroup analysis further revealed that the joint effect of high TyG and high BRI on dementia risk was more pronounced among participants aged ≥65 years(OR=2.68, 95%CI:1.62-4.44) and among current smokers(OR=3.29, 95%CI:1.53-7.08). Conclusions Both TyG and BRI are significantly associated with dementia. The combined assessment of TyG and BRI enhances the predictive capability for dementia, underscoring the critical role of insulin resistance and visceral obesity in identifying and screening individuals for dementia risk.

Key words: dementia, triglyceride glucose index, body roundness index, cohort study