Increased Prevalence of Dementia Observed in Older Patients with Hypothyroidism

Chien-Hsian Weng, MD, MPH

Older patients with hypothyroidism had an 81% greater risk of having dementia than their counterparts without the common thyroid disorder, according to new research.

A large-scale case-control study of more than 15,000 patients in Taiwan, provide insight into the increased likelihood of dementia associated with hypothyroidism among patients aged 65 years or older, with results also demonstrating a more than 3-fold increase in risk of dementia among patients requiring thyroid hormone replacement therapy.

“In some cases, thyroid disorders have been associated with dementia symptoms that can be reversible with treatment,” said senior investigator Chien-Hsiang Weng, MD, MPH, a clinical assistant professor of family medicine at Brown University, in a statement. “While more studies are needed to confirm these findings, people should be aware of thyroid problems as a possible risk factor for dementia and therapies that could prevent or slow irreversible cognitive decline.”

Citing a lack of literature on the association between thyroid disorders and dementia in Asian populations, Weng and a team of colleagues designed the current study with the intent of assessing the association of dementia with a diagnosis of hyperthyroid or hypothyroidism using the Taiwanese National Health Insurance Research Database. With 2006-2013 identified as the period of interest, investigators sought to identify all adult patients aged 65 years or older with newly diagnosed dementia without a prior history of dementia or neurodegenerative disease. From their initial search, investigators identified 7843 patients for inclusion in their study.

For the purpose of analysis, investigators identified 7843 adult patients without dementia diagnosis prior to the index date matched with patients from the cohort with newly diagnosed dementia based on age and gender. Diagnoses of hyperthyroidism and hypothyroidism were identified using ICD-9 codes and investigators also required the exact diagnosis in at least 3 outpatient visits or 1 inpatient diagnosis followed by another inpatient or outpatient visit with the same diagnosis. Investigators noted logistic regression models to adjust for sex, age, history of hypertension, diabetes, coronary artery disease, depression, hyperlipidemia, alcohol dependence syndrome, tinnitus, hearing loss, and radioactive iodine treatment when evaluating associations between a diagnosis of hyperthyroidism or hypothyroidism and risk of dementia.

The mean age for the cohort of patients with dementia was 74.9 (SD, 11.3) years and the mean age for the patients without dementia was 74.5 (SD, 11.3) years. Investigators noted significant differences were observed between the case and control groups in risk of developing dementia among those with a history of hypertension (3712 [47.3%] vs 3211 [40.9%]; P <.001), diabetes (2145 [27.3%] vs 1394 [17.8%]; P <.001), coronary artery disease (1176 [15.0%] vs 1001 [12.8%]; P <.001), depression (159 [2.0%] vs 24 [0.3%]; P <.001), tinnitus (167 [2.1%] vs 125 [1.6%]; P=.013), and alcohol dependence (38 [0.5%] vs 2 [0.0%]; P <.001).

In adjusted analyses, results pointed to a significant association between a history of hypothyroidism and risk of dementia among patients aged 65 years or older (aOR, 1.81 [95% CI, 1.14-2.87]; P=.011). However, this increase in risk was not observed among those 50 years or older but younger than 65 years of age (aOR, 2.43 [95% CI, 0.83-7.12]; P=.106). In analyses assessing risk of dementia based on history of hyperthyroidism, no statistically significant associations were observed for patients 50 years or older but younger than 65 years of age (aOR, 0.67 [95% CI, 0.22-1.99]; P=.465) and those aged 65 years or older (aOR, 1.33 [95% CI, 0.91-1.95]; P=.139).

Further subgroup analysis in patients aged 65 years or older with hypothyroidism suggested those who received thyroid hormone replacement therapy were at a more than 3-fold increase in risk of dementia when compared to those with hypothyroidism not receiving thyroid hormone replacement therapy (aOR, 3.17 [95% CI, 1.04-9.69]; P=.043). No statistically significant differences were observed among patients with hyperthyroidism who received treatment in the form of medication or surgery (aOR, 0.55 [95% CI, 0.23-1.31]; P=.178), surgery or surgery and medication (aOR, 1.95 [95% CI 0.15-24.99]; P=.609), and just medication (aOR, 0.50 [95% CI, 0.21-1.21]; P=.125) with risk of dementia.

“We hope these findings will better inform physicians and patients alike of the risk factors of dementia and possible therapies to prevent or slow irreversible cognitive decline,” wrote investigators.

This study, “Thyroid Disorders and Dementia Risk: A Nationwide Population-Based Case-Control Study,” was published in Neurology.