The Association Between Thyroid Stimulating Hormone and Depression: A Historical Cohort Study

Objective: To investigate the association between thyroid-stimulating hormone (TSH) and clinically relevant depression (CRD) in a population-based study. Patients and Methods: Adult patients (≥18 years of age) who received care at Mayo Clinic in Rochester, Minnesota, and completed a TSH and Patient Health Questionnaire - 9 (PHQ-9) within 6 months of each other, between July 8, 2017, and August 31, 2021, were included. Demographics, medical comorbidities, thyroid function laboratory data, psychotropic medications, presence of primary thyroid disorder, thyroid hormone replacement (T4 and/or T3), and mood disorder diagnoses (using International Classification of Diseases, 10^th version, Clinical Modifications codes) were extracted electronically. The primary outcome, CRD, was defined as a PHQ-9 score greater than or equal to 10. Logistic regression analysis was conducted to assess the association between TSH categories (low ≤0.3 mIU/L; normal >0.3-4.2 mIU/L; high >4.2 mIU/L) and CRD. Results: The cohort included 29,034 patients, mean age 51.4 years, 65% females, 89.9% White, and a mean body mass index of 29.9 kg/m². The mean ± standard deviation for TSH was 3.0±8.5 mIU/L, and the mean PHQ-9 score was 6.3±6.2. After adjustment, the odds of CRD were significantly higher among the low TSH category (odds ratio, 1.37; 95% CI, 1.18-1.57; P<.001) compared with the normal TSH category, especially in people 70 years of age or younger compared with people older than 70 years of age. Subgroup analysis did not show an increase in odds of CRD among patients with subclinical/overt hypothyroidism/hyperthyroidism (after adjustment). Conclusion: In this large population-based cross-sectional study, we report that low TSH was associated with higher odds of depression. Future longitudinal cohort studies are needed to investigate the relationship between thyroid dysfunction and depression as well as sex differences.