Iodine is the raw material for synthesizing thyroid hormones, and the growth and development of the brain requires the participation of thyroid hormones, therefore, iodine is an essential nutrient for the normal development of brain tissues. Scientific research has found that the human brain has two developmental and differentiation periods during fetal development, and it is also the period that is most vulnerable to various factors, also known as the vulnerable period. 1, in the fetal age of 10-18 weeks, this is the period of proliferation, development and differentiation of neuroblastoma cells migrate to form the brain tissue; 2, 3 months before the birth of the child until the birth of 3 years of age, that is, the main stage of the completion of the development of the brain. When the thyroid hormone supply is insufficient due to iodine deficiency in the fetus, a series of obstacles to growth and development will occur, the first of which is the stagnation of the development and differentiation of the central nervous system. Brain damage caused by iodine deficiency, even if more iodine is supplemented after the period of brain development, it will not help the damaged brain tissues.