Circadian and circannual variations of thyroid function in children 11 +/- 1.5 years of age with and without endemic goiter.

A group of 194 children 11 +/- 1.5 years of age from Tirgoviste, Romania, an endemic goiter area, were studied over a 24-hr span (six blood samples at 4-hr intervals) during all four seasons. One hundred thirty-four of the children had some clinical evidence of endemic goiter, and 60 had none. Total and free T3 and T4, reverse T3, thyroglobulin, thyroxin-binding globulin (TBG; three seasons only), and TSH were studied. The circadian rhythms were analyzed by cosinor and the circannual variations by ANOVA. Children with and without endemic goiter showed circadian rhythms in all functions studied except free T4 for which no statistically significant rhythm was detected in the children with goiter. There were differences in the acrophase of total T3, free T3, and TBG, with phase advance in the children with goiter in total T3 and free T3 and a phase delay in TBG. Mesor and amplitude showed no differences except in total T4 for which the amplitude in the children with goiter was statistically significantly lower than in the children without goiter. Children with and without endemic goiter showed seasonal variations in total T4 and free T4 as well as total T3, free T3, and reverse T3, with the highest values in the fall; in thyroxin-binding globulin the highest values were in the winter; and in TSH the highest values were in the summer. There was no significant seasonal variation in thyroglobulin. There was no difference in the circannual variation between children with and without endemic goiter.