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.

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.

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.

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.

Not getting enough iodine when kids are growing can hurt their brain development for good, because iodine is needed to make important brain hormones.