Iodine is a thyroid hormone and a component of thyroxine and triiodothyronine. These hormones are needed for the normal growth and development of the central nervous system.
In adults, lack of iodine causes enlargement of the thyroid gland, or goitre. In children, lack of iodine during foetal development or in early childhood causes stunted growth and mental retardation.
The majority of iodine in the Finnish diet is obtained from milk and dairy products. Another important source of iodine is table salt, to which iodine has been added for decades in order to prevent goitre.
Read more about iodine (pdf)