OBJECTIVE: To investigate the relationship between thyroid volume and body composition in schoolchildren 11 to 15 years of age. METHODS: We conducted a cross-sectional study of 126 girls and 86 boys who were living in an urban area and receiving iodine supplementation. The medical history was reviewed. Weight, height, body fat, fat-free mass, and total body water were measured by using a tetrapolar bioelectrical impedance analyzer. Body mass index and body surface area were calculated. Iodine excretion was measured in a morning urine sample by spectrophotometry. Thyroid volume was measured with use of an ultrasound scanner. Thyroid-stimulating hormone was measured from capillary blood samples with use of a neonatal human thyrotropin kit. RESULTS: All study participants were euthyroid. No study participant had urinary iodine excretion of less than 10 mg/L, and two thirds of the study group had iodine excretion of more than 100 mg/dL. Mean thyroid volume increased from 5.35 +/- 1.11 mL in boys at age 11 years to 8.52 +/- 3.32 mL in boys at age 15 years and from 5.95 +/- 1.70 mL to 7.53 +/- 1.92 mL in girls of corresponding ages. In both sexes, thyroid volume correlated better with height (r = 0.33 in girls and 0.50 in boys), weight (r = 0.35 and 0.43, respectively), and body surface area (r = 0.38 and 0.50, respectively) than with body mass index (r = 0.26 and 0.16, respectively). Thyroid volume showed a significant correlation with fat-free mass (r = 0.39 in girls and 0.49 in boys) and no significant correlation with body fat in both girls and boys. CONCLUSION: Thyroid volume is dependent on body size and therefore on growth variables. It depends on fat-free mass as a relatively precise measure of body size and is not related to the fat mass.
OBJECTIVE: To investigate the relationship between thyroid volume and body composition in schoolchildren 11 to 15 years of age. METHODS: We conducted a cross-sectional study of 126 girls and 86 boys who were living in an urban area and receiving iodine supplementation. The medical history was reviewed. Weight, height, body fat, fat-free mass, and total body water were measured by using a tetrapolar bioelectrical impedance analyzer. Body mass index and body surface area were calculated. Iodine excretion was measured in a morning urine sample by spectrophotometry. Thyroid volume was measured with use of an ultrasound scanner. Thyroid-stimulating hormone was measured from capillary blood samples with use of a neonatal human thyrotropin kit. RESULTS: All study participants were euthyroid. No study participant had urinary iodine excretion of less than 10 mg/L, and two thirds of the study group had iodine excretion of more than 100 mg/dL. Mean thyroid volume increased from 5.35 +/- 1.11 mL in boys at age 11 years to 8.52 +/- 3.32 mL in boys at age 15 years and from 5.95 +/- 1.70 mL to 7.53 +/- 1.92 mL in girls of corresponding ages. In both sexes, thyroid volume correlated better with height (r = 0.33 in girls and 0.50 in boys), weight (r = 0.35 and 0.43, respectively), and body surface area (r = 0.38 and 0.50, respectively) than with body mass index (r = 0.26 and 0.16, respectively). Thyroid volume showed a significant correlation with fat-free mass (r = 0.39 in girls and 0.49 in boys) and no significant correlation with body fat in both girls and boys. CONCLUSION: Thyroid volume is dependent on body size and therefore on growth variables. It depends on fat-free mass as a relatively precise measure of body size and is not related to the fat mass.