Why is Iodine necessary? (as in Iodine salt)?

Salt is iodized because years ago the medical profession realized there was an increasing development of goiter, an enlargement of the thyroid gland in the neck. It was proven that the condition could be avoided with the addition of iodyne to the body...the thyroid absorbs it eadily. It was a cheap fix that works cven now. People who ae sensitive can get plain salt fo the same price.