The link between schizophrenia and hypothyroidism: a population-based study

Schizophrenia is considered to be of the severe psychiatric disorders characterized by chronic debilitating course marked with frequent relapses and high clinical and financial burden. Aberrations of thyroid hormone levels have been documented in several psychiatric conditions including bipolar disease. The aim of this study is to provide insight into whether an association exists between hypothyroidism and schizophrenia. A population-based cross-sectional study was conducted using data retrieved from the largest medical records database in Israel, the Clalit Health Services (CHS). Patients were defined as having hypothyroidism or schizophrenia when there was at least one such documented diagnosis in their medical records. The proportion of schizophrenia was compared between hypothyroid and age- and sex frequency-matched healthy controls. A logistic regression model was used to estimate the association between psychiatric manifestations and hypothyroidism in a multivariate analysis adjusted for age, gender, and smoking status. The study included 40,843 patients with hypothyroidism and 40,918 age- and sex frequency-matched controls. The proportion of schizophrenia in hypothyroid patients was higher than that in controls (2.01% vs. 1.25%, respectively, p < 0.0001). Multivariate logistic regression demonstrated a robust independent association between hypothyroidism and schizophrenia (OR 1.62, p ≤ 0.001). Our study confirms a higher proportion of hypothyroidism among patients with schizophrenia. The awareness of such interrelation should drive physicians treating patients with schizophrenia to consider screening for hypothyroidism. Further studies are required to elucidate the underlying mechanism or the common denominator favoring the co-occurrence of schizophrenia and hypothyroidism.