In children, adolescents, and general adults, mild-to-moderate iodine deficiency, defined as urinary iodine concentration between 20–100 μg/L, is not consistently associated with changes in thyroid function markers including TSH, fT3, and fT4; most observational studies report no significant differences, while a few show conflicting directional effects, resulting in insufficient evidence to establish a clear relationship.

Among children, adolescents, and general adults, there is no consistent association between mild-to-moderate iodine deficiency (urinary iodine concentration 20–100 μg/L) and thyroid function markers such as TSH, fT3, or fT4, with most observational studies showing no significant differences, though a few reported conflicting directional effects, leading to an overall conclusion of insufficient evidence to determine a clear relationship.