The impact of thyroid dysfunction on domain-specific cognitive performance: a cross-sectional study

Aims: While thyroid dysfunction has been implicated in cognitive impairment, its domain-specific effects remain unclear. This study investigates the relationship between thyroid status and performance across distinct cognitive domains in older adults. Methods: We analyzed 166 participants (32 controls, 48 mild cognitive impairment, 86 Alzheimer's disease) aged 50-80 years without pre-existing thyroid conditions. Participants underwent comprehensive assessment including Mini-Mental State Exam (MMSE) and Clinical Dementia Rating (CDR). Thyroid status was classified by TSH levels: low (4.78 μIU/ml). Data normality was evaluated using the Shapiro-Wilk test, and non-parametric methods were applied due to non-normal distributions. Spearman’s correlation and Kruskal-Wallis tests were used for bivariate analyses. Chi-square tests assessed associations between thyroid status and categorical variables. A multinomial logistic regression model was employed to identify predictors of thyroid status, with the low TSH group as the reference category. To address class imbalance, the SMOTE technique was applied, and multicollinearity was examined using the variance inflation factor (VIF). Results: Among the MMSE subdomains, recall, orientation, and attention and calculation were significantly associated with thyroid status. Recall was a strong predictor for both normal and high TSH levels. Orientation scores positively predicted normal TSH and negatively predicted high TSH. Attention and calculation was significantly associated only with normal TSH. Additionally, higher CDR scores were significantly linked to high TSH status. Conclusion: These findings suggest that rather than evaluating global cognition, domain-specific cognitive assessment may provide more meaningful insights into the cognitive effects of thyroid dysfunction.