Abstract
Hypothyroidism is a widespread condition in the United States, affecting approximately 5% of the adult population. Although the clinical use of levothyroxine is well understood, its effect on preventing dementia is not well established. While the exact role of thyroid hormones in the adult brain is unknown, it is apparent that poor thyroid function can lead to mood swings, cognitive impairment, and other psychiatric symptoms. Most studies demonstrate an association between thyroid health and cognition, specifically slow processing of information, decreased effectiveness of executive functions, and lack of learning. This study aims to review the effect of levothyroxine on dementia. We searched electronic databases such as PubMed, Google Scholar, Science Direct, Cochrane, gray literature, and the references of included articles to find relevant articles. Two investigators independently identified eligible studies, screened title/abstract, and extracted data. We identified a total of 319 citations through a database search with six studies (case-control, longitudinal, cross-sectional, randomized controlled trials) meeting the inclusion criteria. Studies with moderate to low risk of bias were evaluated using their respective quality check tools. Five of six studies showed a positive impact of levothyroxine (LT-4) on dementia. According to these studies, the plausible rationale behind the reversal of memory with LT-4 treatment is restoring thyroid-stimulating hormone (TSH), thyroxine (T4) levels, and gamma-aminobutyric acid (GABA) concentrations. People with abnormal thyroid function should be screened for cognitive dysfunction using specific neurocognitive tests and start treatment with LT-4 regardless of symptom presentation. Multi-dose randomized placebo-controlled intervention studies are recommended to assess the effect of LT-4 on lowering the risk of dementia in hypothyroid patients.