1. This retrospective, multicohort study demonstrated no cross-sectional or longitudinal associations between thyroid dysfunction and global cognition, memory, executive function, or dementia.
Evidence Rating Level: 2 (Good)
Study Rundown: Current clinical guidelines suggest that thyroid dysfunction is a treatable and reversible cause of cognitive decline and dementia. However, observational studies have demonstrated mixed results on whether there is a definite association. This retrospective, multicohort, observational study examined the cross-sectional and longitudinal associations between thyroid dysfunction and cognitive decline. Participants were divided into five groups: overt hyperthyroidism, subclinical hyperthyroidism, subclinical hypothyroidism, overt hypothyroidism, and euthyroidism (reference standard). The primary outcome was global cognitive function, using one of several verified cognitive scales. Upon cross-sectional and longitudinal assessments, there were no associations between thyroid dysfunction and cognitive test scores (global cognition, executive function, and memory). Notably, subclinical hypothyroidism had better performances in executive function (standardized mean difference: 0.07 [95% CI: 0.01-0.13]; p= 0.03) and memory (standardized mean difference: 0.08 [95% CI: 0.01-0.15]; p= 0.03) than those who were euthyroid. Furthermore, there was no longitudinal association found between thyroid dysfunction and the development of dementia. The hazard ratios for the development of dementia were 1.54 (95% CI: 0.76-3.10) and 0.79 (95% CI: 0.48-1.28) for overt hyperthyroidism and overt hypothyroidism, respectively. Overall, this study demonstrated a lack of association between cognition and thyroid dysfunction. One limitation of this study, however, is that many individuals receive treatment for thyroid dysfunction; therefore, further investigation is required to determine if untreated thyroid dysfunction in the long term is associated with cognitive decline.
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