Association of Hypothyroidism and the Risk of Cognitive Dysfunction: A Meta-Analysis

Objectives: The purpose of this meta-analysis was to assess whether there is an association between hypothyroidism and the risk of cognitive dysfunction. Methods: PubMed, Cochrane Library, and Embase were searched for relevant studies published from database inception to 4 May 2022, using medical subject headings (MeSHs) and keywords. Results: Eight studies involving 1,092,025 individuals were included, published between 2010 and 2021. The pooled analysis showed that there was no association between hypothyroidism and cognitive dysfunction (OR = 1.13, 95% CI = 0.84–1.51, p = 0.426), including both all-cause dementia (OR = 1.04, 95% CI = 0.76–1.43, p = 0.809) and cognitive impairment (OR = 1.50, 95% CI = 0.68–3.35, p = 0.318). Neither overt hypothyroidism (OR = 1.19, 95% CI = 0.70–2.02, p = 0.525) nor subclinical hypothyroidism (OR = 1.04, 95% CI = 0.73–1.48, p = 0.833) was associated with cognitive dysfunction. Neither prospective cohort (OR = 1.08, 95% CI = 0.77–1.51, p = 0.673) nor cross-sectional studies (OR = 1.23, 95% CI = 0.63–2.42, p = 0.545) had any effect on the association. Interestingly, the risk of cognitive dysfunction was significantly increased in the group not adjusted for vascular comorbidity (OR = 1.47, 95% CI = 1.07–2.01, p = 0.017), while it was reduced in the adjusted group (OR =0.82, 95% CI = 0.79–0.85, p < 0.001). Conclusions: This meta-analysis shows that hypothyroidism was associated with a reduced risk of cognitive dysfunction after adjustment for vascular-disease comorbidities. More prospective observational studies are needed in the future to investigate the relationship between hypothyroidism and cognitive dysfunction.