Thyroid Disorders and Dementia Risk

Abstract

Background and ObjectivesDementia has been gaining attention in aging societies and is estimated to affect 50 million adults globally in 2020, and 12% of the US population may develop a thyroid disorder in their lifetime. There have been limited studies investigating the correlation between thyroid disorder and dementia in the Asian population.MethodsOur large nationwide population-based case-control study used the Taiwanese National Health Insurance Research Database. A total of 7,843 adults with newly diagnosed dementia without a history of dementia or neurodegenerative disease between 2006 and 2013 were identified and included in our study. In addition, 7,843 adults without dementia diagnosis before the index date were age and sex-matched as controls. Diagnosis of hyperthyroidism or hypothyroidism before the diagnosis of dementia or the same index date was identified. Results were obtained from logistic regression models and adjusted for sex, age, history of hypertension, diabetes, coronary artery disease, depression, hyperlipidemia, alcohol dependence syndrome, tinnitus, hearing loss, and radioactive iodine treatment.ResultsA total of 15,686 patients were included in the study. Both case and control groups were slightly predominantly female (4,066 [51.8%]). The mean (SD) age for those with dementia was 74.9 (11.3) years and for those without dementia was 74.5 (11.3) years. Among patients aged 65 years or older, a history of hypothyroidism was associated with an increased risk of being diagnosed with dementia (adjusted odds ratio [aOR] 1.81; 95% CI 1.14–2.87; p = 0.011), which was an association not present in patients older than 50 years but younger than 65 years. We found that this association was most significant among patients aged 65 years or older with a history of hypothyroidism who received hypothyroidism medication (aOR 3.17; 95% CI 1.04–9.69; p = 0.043).DiscussionOur large-scale case-control study found that among people aged 65 years or older, those with a history of hypothyroidism were associated with an 81% increased risk of having dementia and among those, there was a more than 3-fold increased dementia risk with thyroid conditions that required thyroid hormone replacement treatment. Future well-controlled prospective longitudinal studies should be conducted to elucidate these potential mechanisms and relationships.Classification of EvidenceThis study provides Class III evidence that among patients aged 65 years or older, a history of hypothyroidism was associated with an increased risk of being diagnosed with dementia.

Impaired Sensitivity to Thyroid Hormones is Associated with Mild Cognitive Impairment in Euthyroid Patients with Type 2 Diabetes

“… 7 , 8 Previous studies have confirmed that both overt hypothyroidism and overt hyperthyroidism are closely related to cognitive dysfunction. 9 , 10 Similarly, subclinical hypothyroidism and subclinical hyperthyroidism may also increase the risk of cognitive impairment. 10 , 11 Even in the euthyroid population, changes in serum thyroid-stimulating hormone (TSH) and thyroid hormones may affect cognitive function.…”

“… 9 , 10 Similarly, subclinical hypothyroidism and subclinical hyperthyroidism may also increase the risk of cognitive impairment. 10 , 11 Even in the euthyroid population, changes in serum thyroid-stimulating hormone (TSH) and thyroid hormones may affect cognitive function. A prospective cohort study found that a lower serum free triiodothyronine (FT3) level, but still within the normal range, was associated with an increased risk of Alzheimer’s disease (AD).…”

Hyperthyroidism-Induced Upregulation of Neurodegeneration-Related Gene Expression in Metaplasticity-Induced Hippocampus

“…Based on the hippocampus expression of numerous neurodegenerative proteins, we evaluated the influence of hyperthyroidism on LTP inhibition-related gene expression. Clinical and epidemiological studies suggest an association between thyroid hormone dysregulation and the risk of cognitive impairment [12]. Synaptic plasticity is an essential process in memory formation that is regulated by changes in the expression and activity of several intracellular proteins [13].…”

Shared genetic etiology between hypothyroidism and complex diseases: a large-scale genome-wide cross-trait analysis

“…In addition to determining what factors are responsible for the pathophysiology of hypothyroidism, the consequences of hypothyroidism for complicated diseases are gaining attention. Among older patients (aged over 65 years), a large-scale case-control study found that a history of hypothyroidism increased the likelihood of being diagnosed with dementia [5]. Clinical observation studies showed that hypothyroidism was associated with sarcoidosis and chronic rhinitis [8, 9].…”