Correlation between thyroid hormone levels and cognitive dysfunction in older patients with subclinical...

To investigate the correlation between thyroid hormone levels and cognitive dysfunction in older patients with subclinical hypothyroidism (SCH).

A retrospective matched case-control study (1:2 ratio) was conducted, enrolling 420 participants aged ≥ 60 years (140 SCH cases, 280 euthyroid controls) matched by gender, age (± 5 years) and education level. Thyroid function parameters, including thyroid-stimulating hormone (TSH), free triiodothyronine (FT3), free thyroxine (FT4), thyroid peroxidase antibody (TPOAb), and thyroglobulin antibody (TgAb), and cognitive performance assessed via the Mini-Mental State Examination (MMSE), Montreal Cognitive Assessment (MoCA), Alzheimer's Disease Assessment Scale-Cognitive Subscale (ADAS-Cog), Auditory Verbal Learning Test (AVLT), Trail Making Test (TMT), and Stroop Color and Word Test (Stroop Test) were measured.

The SCH patients had TSH levels consistent with the grouping criteria (TSH > 4.2 mIU/L), higher thyroid autoantibody positivity, and poorer cognitive performance across all domains (all P < 0.001). A dose-response relationship was observed between increasing TSH levels and worsening cognitive function. Multivariate logistic regression identified TSH (odds ratio, OR = 1.19), FT3 (OR = 0.68), age, education and APOE ε4 carrier status as independent predictors of cognitive impairment (ROC AUC = 0.786). Stratified analyses showed stronger associations in females and those aged < 75 years, whereas the significance of the correlation between TSH and cognitive impairment was lost in patients aged ≥ 75 years. Sensitivity analyses confirmed the robustness of the findings.

The SCH is independently associated with cognitive dysfunction in older people, with thyroid hormones playing a critical role. The findings suggest potential clinical implications for thyroid function monitoring and cognitive protection in this population.