2. Effect on growth and development: For children, it can promote the development of bones, muscles and sexual function.

3. The development and growth of nervous system must have thyroid hormone. There are two critical periods in human brain development: one is intrauterine period, that is, from pregnancy to birth; The other is 0 ~ 2 years old after birth. In these two periods, the intrauterine period is more important. Iodine deficiency in critical period may lead to brain development retardation. After two years old, even if iodine is supplemented again, it will still cause lifelong mental disability.

Iodine is an essential trace element for human body and an important component of thyroid hormone. Iodine deficiency or iodine excess will bring harm to human body, so iodine is closely related to human health.

Iodine is widely distributed in nature, rocks, soil, water and air, and contains trace amounts of iodine. Iodine in food mainly comes from soil and water, and the iodine content in seafood such as kelp, laver, shellfish and marine fish is the highest, followed by eggs, milk and meat. Cereals, vegetables and fruits have the lowest iodine content.

The iodine content of normal people is about 30 mg (20 ~ 50 mg), and the thyroid organs contain at most 8 ~ 15 mg. A small amount of iodine is also concentrated in the blood of kidneys, salivary glands, stomach glands and mammary glands.

There are three sources of human iodine: 80 ~ 90% comes from food; 10 ~ 20% comes from drinking water; Only about 5% comes from air. ?

In a steady state, the amount of iodine mainly excreted from urine is equal to the amount of iodine ingested. Urine iodine accounts for 85 ~ 90% of total iodine production. ?

The demand and supply of iodine for human body are as follows: the demand is 100 μ g/day, and the minimum value is 44 ~ 75 μ g/day; The supply should be twice the physiological requirement, namely 1.50 μ g/day, including 70 μ g/day for children under 4 years old, 0/.50 μ g/day for adults over 4 years old, and 200 μ g/day for pregnant women and nursing mothers.