The Relationship between Thyroid Function and Depressive Symptoms—the FIN-D2D Population-Based Study

The association between thyroid function and depression is controversial. Both conditions express many similar symptoms, but the studies done give conflicting results. This study draws on a random, population-based sample of 4500 subjects aged 45–75 years old from Finland. The basic clinical study was done in 2007 for 1396 men and 1500 women (64% participation rate). Thyroid stimulating hormone (TSH), free thyroxine (F-T4), and free triiodothyronine (F-T3) were measured in 2013 from frozen samples. The 21-item Beck Depression Inventory (BDI-21) was applied to assess depressive symptoms (score ≥10 points). The prevalence of depressive symptoms was 17.5% in women and 12.5% in men. In women, the mean levels of TSH, F-T4, and F-T3 without depressive symptoms vs. with the presence of depressive symptoms were 1.92/1.97 mU/L, 13.1/13.1 pmol/L, and 3.91/3.87 pmol/L (NS), respectively. In men, the levels were 1.87/1.94 mU/L, 13.5/13.7 pmol/L, and 4.18/4.12 pmol/L (NS), respectively. In multiple regression analysis, TSH had no relationship to BDI-21 total score. We found no association between depressive symptoms and thyroid values.