Can Thyroid Hormone Supplementation Reduce the Risk of Cognitive Disorders?
The recent systematic literature review presented below, published by authors from the California Institute of Behavioral Neurosciences and Psychology (CIBNP), focused, among other things, on potential associations between hypothyroidism and dementia and the impact of related therapeutic interventions in terms of improving cognitive functions.
Possible Connections Between Hypothyroidism and Dementia
Hypothyroidism is a common pathological condition characterized by insufficient production of thyroid hormones. According to data from the USA, for example, it affects 21% of women and 16% of men over the age of 74. This insufficiency subsequently negatively impacts physiological, metabolic, and cognitive functions.
The concentration of thyroid hormones in the brain is reflected by the peripheral level of thyroxine (T4). In overt hypothyroidism, thyroid hormones are below the reference range with elevated levels of thyroid-stimulating hormone (TSH). In subclinical hypothyroidism, the state of thyroid hormones is biochemically detected within normal limits, with elevated TSH levels. Even minimal changes in the concentrations of triiodothyronine (T3) and T4 in the brain can affect behavior. Thyroid hormones have a large number of receptors in the hippocampus and play an important role in neurogenesis, cellular proliferation, and differentiation of granular cells.
Dementia is the progressive deterioration of cognitive functions that makes it difficult to perform everyday activities. It usually occurs in the older population over the age of 70, and in the USA, its prevalence reaches 10%. The most common manifestations of dementia are neurocognitive changes (problems with memory and attention) and depression.
Evaluated Studies
Keywords hypothyroidism, levothyroxine, and dementia were used to find relevant publications in available databases. A total of 319 publications were found. After reviewing inclusion/exclusion criteria and evaluating the quality of work, the authors included 6 studies (case-control, longitudinal, cross-sectional, randomized controlled) published between 2011 and 2021, involving a total of 976 patients.
Findings
Improvement in at least one domain of cognitive functions was found in 5 included studies. These studies offer an explanation for memory improvement after levothyroxine treatment, restoration of TSH and T4 levels, and gamma-aminobutyric acid (GABA) concentration. In 1 study (n = 737), no statistically significant improvement was observed.
Recommendations for Practice
The authors further recommend conducting cognitive function tests in patients with abnormal thyroid function and starting substitution therapy regardless of symptoms.
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Source: Uma D., Rabbani R., Lee J. H. et al. Does hormone supplementation with levothyroxine improve hypothyroid impaired cognitive dysfunction? Cureus 2021 Sep 11; 13 (9): e17885, doi: 10.7759/cureus.17885.
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