According to the Journal of Clinical Endocrinology and Metabolism, one-third of the world's population lives in areas of Iodine deficiency. It is widely known that Iodine deficiency results in goiter and hypothyroidism, but J. Charles Hakala, Dr. Abraham, and Dr. Flechas have explored the optimum levels of Iodine intake for greatest mental and physical health.
They observed that the Japanese diet contains a large about of seaweed, this population ingests roughly 13.8mg daily, without ill effects. In fact, there is evidence of very low incidence of fibrocystic disease in breast tissue and low mortality rates for cancers of the female reproductive organ in Japans. Their levels of ingestion are far above the recommended daily amount of Iodine in North America, indicating that we are missing out on this essential element.
The complete research paper can be found here.