Thyroid hormone: Influences on mood and cognition in adults.

The association of thyroid dysfunction with alterations in mood and cognition has been recognised since some of the earliest descriptions of thyroid disease. Over the years, researchers have aimed to further define these effects throughout the spectrum of thyroid disorders, to better understand the underlying condition and refine indications for treatment. More recently, attention has turned towards examining the impact of differences in thyroid hormones within the normal reference range, particularly in older adults, providing new insights into the association of thyroid hormone with cognitive decline. This review summarises the evidence assessing the influence of thyroid hormone on mood and cognition in overt and subclinical hypothyroidism, within the reference range, and in subclinical and overt hyperthyroidism. Treatment of overt thyroid dysfunction largely resolves associated disturbances in mood and cognitive dysfunction, however in the setting of overt hypothyroidism subtle detrimental effects on cognition may not be fully reversed. Subclinical hyperthyroidism and higher free thyroxine (FT4) within the normal range have been associated with poorer cognitive outcomes. Future research including randomised controlled trials are required to confirm causality and guide the assessment of benefits vs risks of intervention in the increasing population of older adults with subclinical thyroid disease.