No link between subclinical hypothyroidism, major depressive disorder among adolescents
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Adolescents with subclinical hypothyroidism do not have an increased risk for major depressive disorder compared with those with normal thyroid function, according to a study published in Thyroid.
“The directional relationship between subclinical hypothyroidism and prospective major depressive disorder risk has not yet been studied in adolescents in epidemiological studies,” Raphael Hirtz, MD, PhD, senior researcher in the division of pediatric endocrinology and diabetology, department of pediatrics II at University Hospital Essen in Germany, and colleagues wrote. “However, considering that thyroid function and major depressive disorder risk are subjected to maturational processes, especially during puberty, findings from adults may not readily transfer to adolescents. Thus, we conducted the first study to prospectively investigate this association in a representative and nationwide sample of ... adolescents.”
Researchers analyzed data from the German Health Interview and Examination Survey for Children and Adolescents, a nationally representative longitudinal study on the health of children and young people living in Germany. Adolescents aged 10 years or older at baseline who participated in at least one follow-up and provided data on major depressive disorder history were included. Baseline data were collected from 2003 to 2006, and two follow-ups took place from 2009 to 2012 and from 2014 to 2017. Diagnoses of major depressive disorder were reported in either follow-up, and the age of onset of mental health conditions was reported at the second follow-up. Health-related behaviors were reported during baseline and follow-up questionnaires. Blood samples were collected at baseline to measure thyroid-stimulating hormone, free thyroxine and thyroid peroxidase antibodies.
There were 4,118 adolescents included in the study; 111 had subclinical hypothyroidism; three had a TSH level of greater than 10 µIU/mL; 121 reported major depressive disorder. Diagnoses took place a median of 6 years after baseline; median age at diagnosis was 17.84 years.
In both unadjusted and adjusted analysis, subclinical hypothyroidism was not associated with increased odds for incident major depressive disorder. Researchers also analyzed associations after dividing euthyroid adolescents into quartiles based on TSH and free T4 levels. No associations between thyroid hormone levels and incident major depressive disorder were observed.
In sensitivity analysis, thyroid peroxidase antibody positivity was added as an additional confounder of thyroid function. The same findings were observed, with no association between thyroid function and major depressive disorder.
The researchers cited several possible reasons for the study’s findings: Conclusive mechanisms to link TSH levels and mental health are lacking; psychological mechanisms for impaired mental health among people with subclinical hypothyroidism may not hold in population-based studies; and subclinical hypothyroidism may be a transient condition for children and adolescents.
“This finding is embedded into an emerging theoretical framework, also relying on most recent insights from genetics that subclinical hypothyroidism and major depressive disorder do not seem to be related,” the researchers wrote. “Although this seems to hold at the population level, this may not apply to clinical samples. Thus, a longitudinal study, setting in before major depressive disorder occurs and in long-term sequel to a first major depressive disorder, could help clarify their causal relationship.”
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