Excessive iodine intake can also lead to thyroid enlargement and thyroid disease. High iodine substances such as kelp, laver and seaweed paste should not be excessively supplemented in daily life.

Iodine deficiency–induced goiter was prevalent in Taiwan in the past. In 1966, Taiwan began to implement the salt iodization (potassium iodate) policy, so that each gram of salt contains 20 micrograms of iodine for the general public, in order to achieve the goal of preventing and curing iodine deficiency. Animals and vegetables in the sea are rich in iodine, so it was previously thought that eating kelp can treat goiter.

In addition to inadequate iodine intake, early scientists found that goiter occurred when rabbits were fed cabbage or rats for cruciferous seeds, cassava or thiocyanate and thiourea. These ingredients, known collectively as goitrogens, interfere with the use of iodine or the secretion and metabolism of thyroxine. Long-term ingestion of goiter-inducing factors and low iodine intake can easily lead to goiter, but if iodine intake is sufficient, it can counteract the interference.

The symptoms caused by iodine deficiency are generally referred to as "iodine deficiency disorder." The main symptoms in adults are thyroid insufficiency, goiter, low body temperature, aversion to cold, and slow response. Iodine deficiency in childhood can cause goiter, cretinism in severe cases, brain injury and mental retardation, deafness and mutism, spastic paralysis of hands and feet. Iodine is excreted from the urine, and the urinary iodine concentrations decrease when iodine is deficient. The World Health Organization (WHO) sets the urinary iodine concentration less than 100 micrograms/liter as the screening standard for iodine deficiency.

The recommended daily iodine intake for Taiwanese is 90 mg for preschool children; 100-110 mg for 6-12-year-old primary school children; 120-130 mg for 12-18-year-old adolescents; 140 mg for adults; 200 mg for pregnant women and 250 mg for lactating women.

Recommended Daily Iodine Intake (mg)

Thyroxine is synthesized in the thyroid gland. When iodine deficiency occurs, the concentration of thyroxine in the blood drops, stimulating the pituitary gland to secrete thyroid stimulating hormone (TSH), which can promote the thyroid hormone secretion and tissue enlargement. Overstimulation causes goiter. However, excessive iodine intake can also cause goiter, so iodine should not be excessively supplemented in daily life. Especially for patients with known thyroid problems, iodine supplementation should be discussed with your pharmacist first.