The advice given by clinicians on whether to supplement or avoid iodine is inconsistent and often confusing to patients. First of all, it is important to clarify that increased iodine intake is significantly associated with the development of hypothyroidism. Iodine excess (MUI 201-300 μg/L) and iodine excess (MUI >300 μg/L) can lead to a significant increase in the prevalence and incidence of autoimmune thyroiditis and hypothyroidism, as well as a significant increase in the probability of hypothyroidism in people with positive autoantibodies to the thyroid gland. In addition, iodine supplementation in iodine deficient areas to iodine excess can promote the development of subclinical hypothyroidism to clinical hypothyroidism. Therefore, the basic measure to prevent hypothyroidism is to maintain iodine intake in the safe range of 100-200 μg/L of urinary iodine, which is more important for susceptible people with genetic background, positive thyroid autoantibodies and subclinical hypothyroidism. However, this does not mean that all patients with hypothyroidism need to control their iodine intake. On the contrary, patients with hypothyroidism during pregnancy and lactation should always take appropriate iodine supplementation for fetal and pediatric thyroid needs, usually 250ug/day but not more than 500ug/day, and the ideal range for urinary iodine is 150-250ug/L.