In pregnant women with mild iodine deficiency, taking 200 micrograms of iodine daily is linked to a small but measurable reduction in the levels of thyroid hormones called free and total thyroxine during the later stages of pregnancy.

Pregnant women with slightly low iodine levels don’t seem to have noticeable changes in their thyroid hormones compared to those with good iodine levels — their thyroid still works fine even if their iodine isn’t perfect.

Giving iodine supplements to pregnant women with mild iodine deficiency does not reduce the occurrence of isolated hypothyroxinemia or subclinical hypothyroidism, even when urinary iodine levels rise, suggesting the supplements do not resolve the underlying thyroid hormone imbalance.

Taking standard iodine supplements during pregnancy can raise iodine levels in urine beyond the safety threshold recommended by the WHO, even in women who are only mildly deficient.

In children with a mild form of congenital hypothyroidism and an intact thyroid gland, giving iodine supplements does not change how their thyroid function develops over time, based on measurements taken after stopping iodine and during one year of monitoring.

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.