Gender, age, puberty, and BMI related changes of TSH and thyroid hormones in schoolchildren living in a long-standing iodine replete area

Abstract

The aim of the work was to assess thyroid function in children and adolescents in an iodine replete area and to explore possible effects of age, gender, puberty, and adiposity. Thyrotropin (TSH), total triiodothyronine (T (3)), total thyroxine (T (4)), free thyroxine (FT (4)), and the T (4)/T (3) ratio were determined for 440 schoolchildren (200 boys and 240 girls), aged 5-18 years, living in an iodine replete region. Body Mass Index (BMI), BMI standard deviation score (BMI-SDS), and Body Surface Area (BSA) were calculated. In girls there was a negative correlation of TSH, T (3), and FT (4) values with age. In boys there was a negative correlation only of T (3) values with age. Girls had lower TSH, T (4), and T (3) values, whereas boys had only lower T (3) values at puberty compared to the prepubertal stage. Girls had lower TSH values than boys (p<0.03) only at puberty. BMI-SDS in boys and girls were 0.21 and 0.03, respectively. BMI-SDS was not related to TSH, T (4), or T (3) in either gender, whereas it was negatively related to T (4)/T (3) ratio in boys and to FT (4) in girls. We conclude that estrogens may exert a suppressive effect on the pituitary-thyroid axis after puberty. TSH values are not correlated with BMI-SDS, whereas T (4)/T (3) ratio in boys and FT (4) in girls are negatively correlated with BMI-SDS.