Thyroid Hormones Are Associated With Cognitive Function: Moderation by Sex, Race, and Depressive Symptoms

Context: Recent evidence indicates that thyroid hormones may be closely linked to cognition among adults. Objective: We investigated associations between thyroid hormones and cognitive performance, while testing effect modification by sex, race, and elevated depressive symptoms (EDS). Design: This cross-sectional study used extensive data from the Healthy Aging in Neighborhoods of Diversity across the Life Span (HANDLS) study. Setting: The study was conducted in Baltimore, Maryland, from 2004 to 2009. Participants: Participants were U.S. adults aged 30 to 64 years. The sample size ranged from 1275 to 1346. Main Outcome Measures: Outcomes included 13 cognitive test scores spanning domains of learning/memory, language/verbal, attention, visuo-spatial/visuo-construction, psychomotor speed, executive function, and mental status. Results: Within reference ranges and after Bonferroni correction, elevated free thyroxine (fT(4)) was associated with better performance on tests of visuo-spatial/visuo-construction ability (overall, women, and African Americans) and learning/memory (women and African Americans), whereas a higher total thyroxine (tT(4)) level was associated with better performance in the domain of psychomotor speed (individuals without EDS) and higher levels of both fT(4) and tT(4) were linked to better language/verbal test performance among men. In contrast, higher T3(% uptake) was related to better performance on tests of visuo-spatial/visuo-construction ability and psychomotor speed among whites. When the above reference range was compared within the overall population and after Bonferroni correction, a within reference range fT(4) was linked to better performance on visuo-spatial/visuo-constrution ability and psychomotor speed, whereas a below normal range TSH level (compared with the reference range) was linked to better performance in domains of psychomotor speed and attention. Conclusions: Thyroid hormones and cognition are closely linked differentially by sex, race, and EDS status.