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

Akintola, Abimbola A.; Jansen, Steffy W. M.; van Bodegom, David; van der Grond, Jeroen; Westendorp, Rudi G. J.; de Craen, Anton J.M.; van Heemst, Diana · 2015 · OpenAlex-citations

DOI: 10.3389/fnagi.2015.00150

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Summary

This systematic review and meta-analysis investigates the association between subclinical hypothyroidism (SCH) and cognitive function in community-dwelling adults aged 60 years and older. While overt hypothyroidism is well-established as a cause of cognitive deficits, evidence regarding SCH—defined as elevated thyroid-stimulating hormone (TSH) with normal free thyroxine (fT4)—has been conflicting. Given the high prevalence of SCH in older adults, the authors aimed to synthesize available evidence to determine if SCH is associated with cognitive impairment or accelerated decline. The researchers conducted a comprehensive literature search across seven databases (including PubMed, EMBASE, and COCHRANE) from January 1966 to April 2015. Two independent reviewers screened 844 initially identified reports, applying strict inclusion criteria: studies must involve relatively healthy, community-dwelling participants over 60, define SCH clearly, and specify cognitive domains. After excluding duplicates, irrelevant studies, and those involving participants with dementia, depression, or neurological disorders, 15 observational studies comprising 19,944 subjects (1,199 with SCH) were included. The studies utilized various cognitive tests, which were categorized into global cognition, executive function, and memory. Methodological quality was assessed using 11 key indicators. Meta-analysis was performed using random-effects models to calculate pooled effect sizes (ES) for cross-sectional associations and prospective cognitive decline. The results indicated no significant association between SCH and cognitive impairment. For global cognition, assessed primarily via the Mini-Mental State Examination (MMSE), the pooled cross-sectional ES was −0.01 (95% CI −0.09, 0.08). Similarly, pooled ES for executive function was <0.001 (95% CI −0.10, 0.09), and for memory, it was 0.01 (95% CI −0.12, 0.14). Heterogeneity was moderate for global cognition (I² = 55.1%) and memory (I² = 46.9%), but low for executive function (I² = 13.5%). A prospective analysis of four studies also found no significant link between SCH and accelerated cognitive decline, with a pooled ES of 0.033 (95% CI −0.001, 0.067) for MMSE. The study concludes that there is no evidence supporting an association between subclinical hypothyroidism and cognitive impairment in relatively healthy older adults. These findings suggest that SCH may not be a significant risk factor for cognitive decline in this population, contrasting with the established risks associated with overt hypothyroidism. This clarification helps resolve conflicting data in the field and may inform clinical guidelines regarding the monitoring and treatment of SCH in the elderly.

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• cognitive impairment