One sign of insufficient iodine is a swelling of the neck, known as a goiter. The thyroid gland in the neck uses iodine to produce hormones that regulate the heart rate and other body functions. When there's not enough iodine, the thyroid gland enlarges as it goes into overdrive to make up for the lack of iodine.

Although most people are still getting enough, researchers have increasingly been reporting low levels of iodine in pregnant women and other people, raising concerns about an impact on their newborns. And there is also a very small, but growing, number of reports of iodine deficiency in kids.

A century ago, iodine deficiency affected kids across large swaths of America. It essentially disappeared after some food makers started adding it to table salt, bread and some other foods, in one of the great public health success stories of the 20th century.