In children aged 7–14, the size of the thyroid gland and the presence of goiter are better signs of thyroid stress caused by too much iodine over time than blood levels of thyrotropin or thyroglobulin, because they change more consistently with the amount of iodine consumed.

In Chinese children between 7 and 14 years old, consuming iodine at levels of 250–399 micrograms per day is linked to a higher likelihood of developing an enlarged thyroid gland, with higher intake levels corresponding to greater risk.

In parts of Russia where people don’t get enough iodine, about 1 in 5 adults has a swollen thyroid gland, based on ultrasound checks done in large health surveys.

In children with mild thyroid hormone imbalances, taking iodine supplements that gradually increase from 50 to 150 micrograms per day for nine months leads to a measurable increase in TSH hormone levels, but does not change other thyroid markers or cause clinical harm.

In children aged 7 to 14, higher iodine intake is associated with a predictable rise in thyroglobulin levels, but the proportion of children with very high thyroglobulin levels stays above 3% regardless of how much iodine they consume, suggesting that this measure cannot reliably identify excess iodine.

For kids, teens, and adults, not getting quite enough iodine doesn’t seem to clearly affect thyroid hormone levels — some studies see no change, others see mixed results, so we can’t say for sure either way.