Background <p>Metabolic disorders are closely associated with cognitive decline, and the metabolic score for insulin resistance (METS-IR), as a comprehensive indicator reflecting metabolic status, may offer a novel perspective for cognitive function assessment. This study aims to explore the association between METS-IR and cognitive function in older adults and evaluate its potential value in assessing the risk of cognitive impairment.</p> Methods <p>A cross-sectional analysis was carried out utilizing data from the National Health and Nutrition Examination Survey conducted between 2011 and 2014. The relationship between METS-IR and cognitive function was analyzed using weighted multivariable linear regression. Nonlinear relationships were examined using restricted cubic spline techniques and threshold effect analyses. In addition, subgroup interaction analyses were performed based on demographic characteristics, lifestyle factors, and metabolic diseases. Finally, the discriminative ability of METS-IR for cognitive decline was evaluated using receiver operating characteristic curve analysis.</p> Results <p>METS-IR was significantly negatively correlated with all cognitive function test scores. After adjusting for demographic characteristics, lifestyle factors, and metabolic-related diseases, the negative association remained significant. Threshold effect analysis suggested that there is a tipping point, where the association between METS-IR and cognitive impairment becomes more evident. Subgroup analyses indicated that most subgroups did not exert a significant modifying effect on the association between METS-IR and cognitive function; however, smoking may affect the strength of the relationship between METS-IR and cognitive decline. The ROC curves demonstrated that METS-IR demonstrated relatively stable discriminative ability for cognitive decline, highlighting its potential as a supplementary tool for risk stratification.</p> Conclusions <p>Elevated METS-IR is independently associated with cognitive decline in older adults and shows a threshold effect. Its accessibility and stable discriminative ability support its potential as a supplementary tool for risk stratification. Future longitudinal studies are needed to verify the causal relationship and explore the feasibility of improving cognitive function through metabolic interventions. This study provides new evidence for the association between metabolic health and brain health, offering scientific basis for early screening and intervention strategies for high-risk populations.</p>