One of the words we don’t use any more is cretin; it’s long been a derogatory slur rather than a precise description of something. But a century ago cretinism actually meant a specific thing: a person, generally a child, who was severely damaged by a lack of thyroid hormone during early development, particularly fetal development. Now we call the condition congenital hypothyroidism. A few cases still exist, which is why we screen all newborns for thyroid function. But the overwhelmingly most common cause a century ago was hypothyroidism — low thyroid hormone — in pregnant women. The overwhelmingly most common cause of that was deficiency of iodine in the diet.
The thyroid gland sits in the front of your neck, just below your voice box (larynx). It has two lobes on either side connected by a little bridge. Its job is to make, store, and release thyroxine, or thyroid hormone. This hormone has several important functions, acting upon nearly every cell in the body in one way or another. It affects the metabolism of cells, how they use energy, and is key to cellular growth and development. The thyroid gland needs iodine to make thyroxine properly. A thyroid that is not making thyroxine properly may swell into a goiter, another thing that once was common and now is rare. There are various reasons adults may develop low thyroxine levels, become hypothyroid. These days this condition is easily treated by taking oral thyroid hormone every day. The problem for a baby developing in the womb is that a deficiency of thyroxine in the mother causes irreversible damage before the baby is born, and thus before we can give the infant thyroid hormone.
Congenital hypothyroidism is now rare in the developed world. Why? You can read the history lesson of why in a nice review here, but the reason is iodine supplementation of food, particularly salt. This is a fascinating example of several companies, particularly the giant Morton Salt Company, listening to the advice of medical experts and then just adding iodine to their product. This turned out to be an easy thing to do.
The result was an astounding public health triumph. Congenital hypothyroidism on the basis of iodine deficiency is still a problem in the developing world, but it has been eliminated from the developed world. To me it brings to mind the addition of fluoride to water and the subsequent dramatic reduction in dental caries in children. Interestingly, although I have a graduate degree in history of medicine, I am unaware of any organized efforts by people to resist iodized salt as there has occasionally been for fluoridated water. You can buy salt without iodine, although I don’t know why you would want to, but salt is found in nearly every food product that has been processed in any way, such as bread. So you can’t really avoid it.
Again, this is an example of a simple, well targeted population intervention, like vaccination, that conquered a disease that had plagued people for millennia.