Iodized salt is mainly for residents in iodine-deficient areas, and non-iodized salt should be purchased in iodine-rich areas. Iodine is one of the essential trace elements for human body, and is known as an intellectual element. The content of iodine in human body is only about 30 mg, half of which is in thyroid and the rest is distributed in other tissues. Iodine is an important raw material for the synthesis of essential thyroid hormone, which affects the production, development and metabolism of the body, and the brain is its first target organ. Iodine deficiency in embryos and infants will lead to mental retardation of different degrees in patients' life. The World Health Organization calls iodine deficiency hazard IDD, which is the main reason for the backward development of human intelligence. It has been proved that most of the development of the human brain is completed in embryo and infancy. In the whole process of intellectual development, if iodine intake is insufficient, it will produce a series of obstacles in the process of growth and development. Even if iodine deficiency is slight, it will cause mild mental retardation and last for life. However, serious iodine deficiency will cause obstacles to children's physical development, that is, short stature, delayed sexual development and low IQ. It can also cause premature birth, stillbirth, congenital malformation, deafness, deafness, dementia and so on. The common diseases are endemic goiter (coarse neck disease) and endemic cretinism. These damages are collectively referred to as iodine deficiency disorders. Iodine exists in nature, and people mainly take it from drinking water, grain, vegetables and the surrounding environment. Due to the differences in age and physiology, the daily iodine requirement of infants under 4 years old is 70 micrograms, that of adults is 150 micrograms, and that of pregnant women and nursing mothers is about 200 micrograms. However, most areas in China lack iodine, and continuous intake of iodized salt can improve intelligence, keep fit and prevent diseases. Taking iodized salt according to the demand of 1 year can avoid giving birth to mentally retarded children. Although iodine is an indispensable trace element for human body, excessive iodine is harmful. In June 2000, the new standard of edible salt implemented by 65438+1 October1adjusted the iodine concentration from 40 mg/kg to 35 mg/kg.