Thyroid activity in patients with major depression

Hypothalamus-pituitary-thyroid (HPT) axis dysfunction has been associated with pathophysiology of major depression. The aim of the study was to determine serum levels of total 3,5,3'-triiodothyronine (T3), total thyroxine (T4) and thyroid-stimulating-hormone (TSH) in patients with major depression and healthy controls. The study included 53 medication-free patients with depression and 49 healthy controls. Exclusion criteria for patients was: other axis-I and axis-II diagnoses, intensive psychotherapy or electroconvulsive therapy, prior clinical and/or laboratory evidence of hypo- or hyperthyroidism, alcohol or nicotine dependence, pregnancy, hormone supplement therapy, somatic illnesses (diabetes, renal or hepatic disorders), infections or autoimmune diseases, recent surgical treatment or significantly changed body weight. For controls: the presence of psychiatric disorders and/or thyroid dysfunctions. The diagnosis of major depression was made using structured clinical interview based on DSM-IV criteria. The results showed significantly lower T3 and TSH levels in patients compared to controls. There was no significant difference in T4 values between patients with depression and control subjects. The results showing altered levels of thyroid hormones in depression indicate that further research on thyroid hormone activity can contribute to the better understanding of the biological basis of depression. Based on the high frequency of the subtle neuroendocrine disorders coexisting with depression, the association of thyroid abnormalities and depression should not be underestimated. Future research should identify different behavioral endophenotypes characteristic for depression, which would greatly facilitate delineating the biological phenomena associated with this psychiatric illness.