Thyroid Hormones Are Associated with Poorer Cognition in Mild Cognitive Impairment

Abstract

Background: Alterations in interrelated endocrine axes may be related to the pathogenesis of mild cognitive impairment (MCI) and dementia. Methods: Salivary cortisol before and after a 0.5-mg dexamethasone test, and serum levels of thyroid-stimulating hormone, total thyroxine (T₄), free T₄, total triiodothyronine (TT₃), estradiol, testosterone and insulin-like growth factor 1 were measured in 43 MCI cases and 26 healthy controls. All participants underwent a comprehensive neuropsychological test battery covering the cognitive domains of speed/attention, memory, visuospatial functions, language and executive functions. Results: The MCI group did not differ in basal levels of endocrine markers compared to controls. Among those with MCI, TT₃ levels were inversely associated with cognitive performance across all domains. After stratifying MCI cases according to TT₃ levels, those with relatively high TT₃ levels showed impairment in memory as well as in visuospatial and executive functions. Those with TT₃ levels at or below the lower boundary of the normal range performed comparably to healthy controls. Other endocrine markers were not related to cognitive performance. Conclusions: Among those with MCI, TT₃ was associated with a neuropsychological profile typical of prodromal Alzheimer’s disease. While the mechanisms remain unclear, optimal levels of thyroid hormone under a compromising condition such as MCI and related neuropathology need reconsideration.

Type II deiodinase polymorphisms and serum thyroid hormone levels in patients with mild cognitive impairment

“…Thus, TH level is one of the main factors affecting cognitive function. This result is consistent with those of Stern et al (2004) and Wang et al (2011), but not with those of Quinlan et al (2010). Recently, an evidence-based analysis examining thyroid and aging reported that subclinical hyperthyroidism was associated with a higher incidence of cognitive impairment, but there was no evidence to support use of antithyroid drugs for dementia (Aggarwal and Ravzi, 2013).…”

“…However, there was no difference in attention, executive function, visuospatial, and word abstract ability. However, a study by Quinlan et al (2010) suggested that among those with MCI, T 3 levels were inversely associated with cognitive performance across all domains. After stratifying MCI cases according to T 3 levels, those with relatively high T 3 levels showed impairment in memory as well as in visuospatial and executive functions.…”

Thyroid Status and Cognitive Function in Euthyroid Patients with Early Parkinson's Disease

“…As in our study that showed no relationship between tT 3 and cognition, previous studies have also failed to identify a significant relationship between cognitive function and T 3 concentrations [20,21,28]. However, another study supported an association between the variability of T 3 levels within the normal range and cognitive dysfunctions [29,30]. The difference in the results may be due to differences in sample selection, age range, choice of cognitive function tests, and the limited number of thyroid function indices.…”

The relationship between thyroid hormone levels and cognitive functions in Graves’ disease might be influenced by a history of mild traumatic brain injury

“…On the contrary, de Jong et al found no such relationship [25]. In an elderly population, dementia or other brain degeneration may influence the results [24]. Moreover, the relation between hormone levels and cognition does not have to be linear, and the balance between hormones could also be an influencing factor [26].…”

“…However in Walsh's study correlation analyses were not performed. In a more elderly population [23] and in patients with mild cognitive impairment [24], high fT3 and high total T3 levels respectively have been associated with impaired cognitive functions. On the contrary, de Jong et al found no such relationship [25].…”