BACKGROUND
Hypothyroidism is very common and can affect up to 15% of certain populations. Hypothyroidism also may become more common with aging, although this is controversial. Decreased concentration and memory issues are symptoms of hypothyroidism that go away on treatment with thyroid hormone. Dementia is a brain disease that causes memory loss, more commonly seen in the older people, and cases are increasing through the years. Because of these similar symptoms, there has been increasing interest in exploring the role of thyroid function, especially hypothyroidism, in dementia. However, studies observing the associations between hypothyroidism and dementia have yielded mixed results. Moreover, the outcomes of the treatment of hypothyroidism in dementia are not clear, particularly with regard to evidence from Asian populations.

This study examines possible link between hypothyroidism and dementia in the East Asian people.

THE FULL ARTICLE TITLE
Wieland DR et al 2022 Thyroid disorders and dementia risk: A nationwide population-based case-control study. Neurology. Epub 2022 Jul 6. PMID: 35794019.

SUMMARY OF THE STUDY
Researchers collected the health records of 7,843 patients who had new-onset dementia without a previous history of dementia between 2006 and 2013 (case group) and matched them 1:1 according to age, sex, and index date (date enrolled in the study) with subjects who had never been diagnosed with dementia (control group). From these participants, those with a history of hyperthyroidism or hypothyroidism within 1 year before the first diagnosis of dementia (case group) or the index date (control group) were then identified.

The study comprised 15,686 adults in the 2 groups (51.8% female) with an average age of ~75 years. There was pre-existing hypothyroidism in 68 (0.9%) of the subjects with dementia, as compared with 34 (0.4%) of those without dementia. After adjusting for multiple factors that could affect the risk of dementia, having a history of hypothyroidism was found to be positively correlated with the risk of being diagnosed with dementia among those 65 years of age or older. There was preexisting hypothyroidism in 76 (1.0%) of the subjects in the dementia group and 57 (0.7%) of those in the control group. No significant correlation between the history of hyperthyroidism and the increased risk of developing dementia was found.

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
This study suggested that East Asian patients over the age of 65 years old with history of hypothyroidism had an increased risk of developing dementia than those without hypothyroidism. However, the overall risk was low (<1%). There was no correlation between hyperthyroidism and dementia. While this association is interesting, more studies are needed to determine the role, if any, of hypothyroidism in developing dementia. This is important for physicians to be aware of this association and to consider evaluating for dementia in elderly hypothyroid patients if symptoms develop.

— Joanna Miragaya, MD

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