Thyroid Function in Korean Adolescents with Obesity: Results from the Korea National Health and Nutrition Examination Survey VI (2013–2015)

PURPOSE: In this study, we investigated the status of thyroid function and its association with metabolic risk factors in Korean adolescents. METHODS: Among 2679 subjects aged 10–19 years who participated in the Korea National Health and Nutrition Examination Survey VI (2013–2015), 1067 adolescents (M = 559, F = 508) with available data on free T4 (FT4) and thyroid-stimulating hormone (TSH) were included. Study participants were classified into normal weight [body mass index (BMI) below 85th percentile, 80.7%], overweight (85th ≤ BMI< 95th percentile, 8.7%), and obesity (BMI ≥ 95th percentile, 10.6%). RESULTS: With increasing levels of BMI category, the means of TSH increased (2.73 ± 0.06, 2.77 ± 0.02, and 3.24 ± 0.22 mIU/L, P = 0.031) and FT4 decreased (1.30 ± 0.01, 1.26 ± 0.02, and 1.25 ± 0.02 ng/mL, P = 0.001). Positive linear associations were observed between TSH and BMI z-score (P = 0.031), waist circumference (P = 0.013), waist-height ratio (P = 0.002), systolic blood pressure (P = 0.001), total cholesterol (P = 0.008), and triglyceride (P = 0.002) after adjusting for age and sex. With per-unit increase in TSH, the odds ratios of having abdominal obesity (OR = 1.18, 95% CI, 1.01–1.38) and triglyceride ≥ 150 mg/dL (OR = 1.18, 95% CI, 1.04–1.34) were significantly increased after adjusting for age, sex, and BMI. CONCLUSIONS: In adolescents with obesity, TSH was higher and FT4 was lower than in adolescents with normal weight. Hyperthyrotropinemia was associated with abnormal metabolic risk factors including abdominal obesity and elevated triglyceride.