Thyroid hormones are associated with longitudinal cognitive change in an urban adult population

Abstract

Recent evidence indicates that thyroid hormones may be closely linked to cognition among adults. We investigated associations between thyroid hormones and longitudinal cognitive change, within and outside of reference ranges, stratifying by sex and race. This longitudinal study used data from the Healthy Aging in Neighborhoods of Diversity Across the Lifespan (HANDLS) study, set in Baltimore City, MD, 2004-2013, on adults aged 30-64y at baseline visit, with a length of follow-up between visits 1 and 2 ranging from <1 year – 8 years; Mean±SD: 4.64±0.93. The final analytic sample sizes ranged from 1,486-1,602 participants with 1.6-1.7 visits/participant (total visits: 2,496-2,757), depending on the cognitive test. Eleven cognitive test scores spanning domains of learning/memory, language/verbal, attention, visuo-spatial/visuo-construction, psychomotor speed, executive function, and mental status were used. Mixed-effects regression models were conducted, interacting time of follow-up with several thyroid exposures. Whites performed better than African-Americans, with only four cognitive test scores of eleven declining significantly over-time. Importantly, above reference range thyroid stimulating hormone (vs. reference range, TSHarr) was linked to faster rates of decline on the Digits Span Backwards test, reflecting working memory (TSHarr×Time γ±SE:-0.14±0.05, P=0.006) and clock-command, a test of visuo-spational/visuo-construction abilities (TSHarr×Time γ±SE:-0.10±0.04, P=0.004). The latter finding was replicated when comparing normal thyroid function to “subclinical hypothyroidism”. Within reference ranges, a higher TSH was related to faster decline on the clock-command test scores in women. In sum, higher baseline TSH was associated with faster cognitive decline over-time among urban US adults, specifically in domains of working memory and visuo-spatial/visuo-construction abilities.

Effect of Thyroid Function Variations Within the Laboratory Reference Range on Health Status, Mood, and Cognition in Levothyroxine-Treated Subjects

“…Two of them are sensitive measures of working memory (N-Back and Subject Ordered Pointing) (42,43). In concordance with the few available reports in non-LT4 treated (7,17) and LT4 treated euthyroid subjects (23,26,27), we did not find associations between thyroid function and these four measures.…”

“…In euthyroid subjects without thyroid disease, depression, anxiety, or cognitive decrements have been linked to variations in TSH or free thyroxine (fT4) levels (4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17). However, the correlations have shown improvements or decrements with higher or lower thyroid function, depending on the report.…”

Dairy product consumption and its association with metabolic disturbance in a prospective study of urban adults

“…This was partly adjusted for using the 2-stage Heckman selection model, as described in previous studies. (91; 92; 93) Moreover, measurement error in dietary exposures can still be sizeable, even though 2 24-hr recalls per wave are an improvement over many large cross-sectional studies. Those errors are probably random across metabolic disturbance groups, leading to attenuation of true associations.…”

“…(90) A probit model was constructed to obtain an inverse mills ratio at the first stage (derived from the predicted probability of being selected, conditional on the covariates in the probit model, mainly baseline age, sex, race, poverty status and education), as was done in earlier studies. (91; 92; 93) This inverse mills ratio was then entered as a covariate in the main models to adjust for sample selectivity. Type I error was set at 0.05.…”

Fragile X-associated tremor/ataxia syndrome — features, mechanisms and management

“…Thyroid function should be checked and any deficiency should be treated, as thyroid deficiency can lead to cognitive decline 141 . Thyroid deficiency is common among patients with FXTAS, as are hypertension and sleep apnoea; each of these conditions can be treated.…”