Subclinical hypothyroidism and cognitive function in people over 60 years: a systematic review and meta-analysis

Abstract

Subclinical hypothyroidism (SCH), defined as elevated thyroid stimulating hormone (TSH) and normal thyroid hormone levels, and cognitive impairment are both common in older people. While the relation between overt hypothyroidism and cognitive impairment is well established, data on the association between SCH and cognitive impairment are conflicting. This systematic review and meta-analysis was performed to assess available evidence on the association of SCH with cognition in community dwelling, relatively healthy older adults. PubMed, EMBASE, Web of Science, COCHRANE, CINAHL, PsycINFO, and Academic Search Premier (January 1966 to April 1, 2015) were searched without language restrictions, as were references of key articles, for studies on the association between SCH and cognition in older adults (>60 years). These studies were reviewed by two independent reviewers according to predefined criteria for eligibility and methodological quality, and data were extracted using standardized forms. Of the 844 reports initially identified, 270 remained after exclusion of duplicates. Of the 270, 15 studies comprising 19,944 subjects, of whom 1,199 had subclinical hypothyroidism were included. Data from the 15 studies was pooled, and meta-analyzed cross-sectionally for global cognition [assessed by Mini-Mental State Examination (MMSE)], executive function, and memory, using random effects models. Pooled effect size (ES) for MMSE was −0.01 (95% CI −0.09, 0.08), with heterogeneity (I2) of 55.1%. Pooled ES was < 0.001 (95% CI −0.10, 0.09) for executive function (I2 = 13.5%), and 0.01 (95% CI −0.12, 0.14) for memory (I2 = 46.9%). In addition, prospective analysis including four studies showed pooled ES of 0.033 (95% CI −0.001 − 0.067) for MMSE (I2 < 0.001%), indicating that subclinical hypothyroidism was not significantly associated with accelerated cognitive decline. This systematic review and meta-analysis provides no evidence that supports an association between SCH and cognitive impairment in relatively healthy older adults.

The association between subclinical thyroid dysfunction and dementia: The Health, Aging and Body Composition (Health ABC) Study

“…We found no significant association of SHypo with either dementia or cognitive decline. This is consistent with the results of two previous meta‐analyses and of the recent TRUST trial that found no benefit of thyroxine replacement on executive cognitive function as measured by the letter‐digit coding test . Conversely, another meta‐analysis found a significant association in participants younger than 75 years only .…”

Thyroid function in elderly people: The role of subclinical thyroid disorders in cognitive function and mood alterations

“…Collectively, the data showed no association between subclinical hypothyroidism and depression or anxiety in older adults, although older adults with higher raised TSH have shown a higher depression rate . Furthermore, a recent systematic review reported that in more than 92% of the population sampled lacks of significant association between subclinical hypothyroidism and cognitive impairment or mood alteration. Given these variable and inconsistent findings, the data do not support the concept that alterations in cognitive functions are associated with subclinical hypothyroidism.…”

Hipotiroidismo Subclínico no Idoso

“…1 Os poucos estudos recentes que investigaram a relação entre o HSC e a função cognitiva no idoso não apresentavam resultados concordantes e consistentes. 15,18,19 Em 2015, Akintola et al 20 concluíram, através de uma meta-análise de 15 estudos, que não existia evidência da associação entre HSC e alterações cognitivas em idosos aparentemente saudáveis. Estas conclusões podem resultar do enviesamento dos resultados, associado ao declínio das capacidades cognitivas no decorrer do processo de envelhecimento.…”