Increased Prevalence of Subclinical Hypothyroidism and Thyroid Autoimmunity in Depressed Adolescents: Results From a Clinical Cross-Sectional Study in Comparison to the General Pediatric Population

OBJECTIVE The study was undertaken to determine the prevalence of subclinical and overt thyroid dysfunction as well as thyroid autoimmunity in depressed adolescents in comparison to the general pediatric population. Additionally, the relationship between parameters of thyroid function and Beck Depression Inventory-II (BDI-II) scores was examined. METHODS Parameters of thyroid function (thyrotropin, free thyroxine, thyroid peroxidase antibodies) and prevalence of thyroid dysfunction and autoimmunity were determined in 360 adolescents (11-19 years) with at least mild depression (BDI-II score > 13) between June 2016 and December 2019 and in a representative reference cohort without evidence of impaired mental health from a nationwide survey (German Health Interview and Examination Survey for Children and Adolescents [KiGGS], 2003-2006). RESULTS There was a higher prevalence of thyroid peroxidase antibody positivity in depressed adolescents (mean ± SD BDI-II, 30.0 ± 10.4) compared to KiGGS participants (depressed adolescents: 5.8%, 95% CI [3.7-8.6]; odds ratio [OR] 1.9, P = .009, d = 0.36; KiGGS participants: 3.1%, 95% CI [2.5-3.9]). The prevalence of subclinical hypothyroidism was likewise higher in depressed adolescents (9.1%, 95% CI [6.3-12.4] vs KiGGS participants: 2.1%, 95% CI [1.6-2.7]; OR 4.7, P < .001, d = 0.85), but no other types of thyroid dysfunction had a higher prevalence. There was no significant relationship between parameters of thyroid function and BDI-II scores, as examined by multiple regression considering relevant covariates. The positive results were verified in a subsample of patients with a confirmed diagnosis of depression (N = 284). CONCLUSIONS The prevalence of subclinical hypothyroidism and of thyroid autoimmunity in depressed adolescents is increased. The etiology of these observations is not well understood, and further studies to examine the underlying relationship are required. Moreover, thyroid autoimmunity may constitute an additional risk factor for depression on its own.