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.

We don't have strong enough proof to say whether mild or moderate iodine deficiency really affects thyroid function, because the studies done so far aren't very reliable or consistent.

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.

People who don’t get quite enough iodine don’t seem to have a clear difference in thyroid problems compared to those who get enough — most studies show no big link, even though a few suggest there might be a small risk.

When kids have more iodine in their urine, fluoride doesn’t seem to make their thyroid gland grow as much—so iodine might help protect their thyroid from fluoride’s effects.

When kids have just enough iodine in their urine but are exposed to more fluoride, their bodies might make less of an important thyroid hormone called TT3 — like their thyroid is struggling a bit under those conditions.