Relationship between serum thyroglobulin, thyroid volume and serum TSH in healthy non-goitrous subjects and the relationship to seasonal variations in iodine intake.

In order to investigate the interrelationship between serum thyroglobulin (Tg), thyroid volume and serum TSH by a sensitive method, 176 healthy euthyroid non-goitrous subjects were studied. Furthermore the seasonal influence, assuming seasonal differences in iodine intake in Denmark, was studied in 13 healthy male volunteers. A weak correlation between serum Tg and thyroid volume was found only in female non-goitrous subjects. No correlations between serum Tg, thyroid volume, free T4 and free T3 indices, T3/T4 ratio, serum TSH by sensitive method or age were seen. Thyroid volume was increased (P less than 0.01) during the winter without any change in thyroid function or TSH level, whereas serum Tg level in these subjects was significantly lower (P less than 0.02) during the winter compared with the summer. In conclusion, serum Tg showed no correlation with either thyroid volume, super-sensitive TSH or thyroid function in a population of non-goitrous subjects in Denmark. The lack of correlation between increased thyroid volume and decreased serum Tg during the winter compared with the summer is unexplained. It might be hypothesised that short-term changes in iodine intake induce only colloid accumulation (i.e. increased thyroid volume) without changes in the glandular secretion of Tg or thyroid hormones.