Iodine and the thyroid gland The thyroid gland is an important endocrine organ in the body whose main function is to synthesize and secrete thyroid hormones. Thyroid hormones have a wide range of functions, as they promote material and energy metabolism, growth and development processes in the human body. Iodine is an essential trace element for the human body and is one of the main raw materials for the synthesis of thyroid hormones. Iodine is widely found in nature and people mainly take it from drinking water, food and the surrounding environment. The iodine requirement varies by age or physiological period, from about 70 micrograms per day for infants under 4 years old to 100-150 micrograms per day for adults and about 200 micrograms for pregnant women and lactating mothers. Insufficient or excessive iodine intake by the body can affect the thyroid gland and the health of the body. The effect of iodine deficiency on the thyroid gland and health is related to the developmental period of the body. For example, iodine deficiency in infancy can affect the neurological and skeletal development of infants and can lead to cretinism in severe cases; iodine deficiency in adults can cause goiter and hypothyroidism. At present, through the universal salt iodization, a simple, safe, effective and economical iodine supplementation measure, the iodine intake of most people can meet the needs of the human body. In addition, regular consumption of foods containing more iodine such as kelp, sea fish, nori and shrimp skin can also prevent insufficient iodine intake. Excessive iodine supplementation can also affect the thyroid gland and the health of the body. Excessive iodine may be associated with autoimmune thyroiditis, hyperiodothyroidism, hypothyroidism, and papillary thyroid cancer. Therefore, more iodine supplementation is not better. Iodine and hyperthyroidism: When hyperthyroidism symptoms are obvious and thyroid hormone levels are higher than normal, as well as before and after 131I treatment, a strict low iodine diet and avoidance of seafood are advocated. During the remission period of hyperthyroidism, the dietary requirements do not need to be very strict, and the intake of iodine can be considered to increase moderately. Iodine and thyroid cancer: Iodine deficiency can lead to a decrease in the synthesis and secretion of thyroid hormones and an increase in the level of thyroid stimulating hormone (TSH), which can lead to hyperplasia of thyroid follicles and even nodules or cancer. A diet high in iodine can also alter the structure and function of the thyroid gland and may increase the incidence of papillary thyroid cancer. The correct approach is to consume iodized salt or iodine-rich foods such as seaweed and nori in moderation to ensure the physiological requirements, but neither too much nor too little is advisable.