Iodine is the raw material for the synthesis of 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 tissue. Scientific research has found that the human brain has two periods of vigorous development and differentiation 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, which is the proliferation of neuroblastoma cells, development and differentiation and migration to form the brain tissue period; 2, 3 months before birth until 3 years old after birth, that is, the main stage of brain development is completed. When the supply of thyroid hormone 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 blockage 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.