Thyroid Disorders and Dementia Risk

BACKGROUND AND OBJECTIVES: Dementia 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. METHODS: Our 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. RESULTS: = 0.043). DISCUSSION: Our 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 EVIDENCE: This 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.