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Obesity is Associated with Changes in the Hypothalamic-Pituitary-Thyroid Axis Leading to Abnormally Low Serum FT4 Concentrations in Children and Adolescents

Erica Haught, Amber Vozar, Sachin V. Bendre

Objective: Central Hypothyroidism (CH) is defined as inappropriately normal or low Thyroid Stimulating Hormone (TSH) levels while free Thyroid hormone (fT4) levels are below normal range. TSH levels above normal range as well as fT4 levels in the lower range of normal have been documented in adults and children with obesity. As there are only a small number of studies looking at thyroid axis abnormalities in children with obesity, we designed this study to document the fT4 and TSH levels in obese children and adolescents.

Methods: This is a retrospective chart study performed in patients from our Pediatric Endocrinology clinic. A total of 1167 charts of children aged 2 to 18 years, that were referred to our clinic for obesity and weight-related co-morbidities were analyzed for BMI, age, sex, TSH and fT4 levels. Only data from subjects showing abnormal thyroid levels suggestive of CH was analyzed and included in the study.

Results: A total of 110 subjects had abnormal thyroid levels. Thyroid functions suggestive of CH were seen in 51 (28 boys and 23 girls) obese children. Interestingly, all patients with CH were pubertal, with an average age of approximately 13.5 years in both sexes. Mildly elevated TSH levels were seen in the remainder of 59 children with no association to pubertal status.

Conclusion: fT4 levels below the normal range in the presence of normal TSH levels, indicative of CH, were seen exclusively in pubertal boys and girls. No pre-pubertal obese children showed this abnormality. We conclude that more studies are needed to establish the causality of this thyroid hormone discrepancy and to formulate a management strategy for this thyroid axis abnormality in obese adolescents.