Evidence has been around for over 50 years on the importance of iodine in regards to the maintenance of healthy breast tissue. An absence of sufficient iodine and its role in the initiation of cancer formation is becoming clearer with modern science.

Sherry Tenpenny, DO - The deficiency of iodine and the disorders it causes!

There seems to be a correspondence with estrogen levels combined with low iodine levels causing the formation of cancer cells in breast tissue. Here is an extract from one of the studies Sherry Tenpenny uses for reference.

Effect of iodide-deficiency on rat mammary gland.
Strum JM.

Abstract
When rats are kept iodide-deficient, atrophy and necrosis takes place in the mammary gland and areas of dysplasia and atypia are seen. Administration of estradiol to iodide-deficient rats stimulates cell division in the gland and leads to the formation of alveoli. Continued stimulation by estradiol produces changes in the newly-formed alveolar cells. Their nucleoli are altered and show a separation of components. Ribosomes and lipid droplets increase and the cells synthesize large vacuoles containing protein. The secretion of great quantities of this material into areas of the tissue where regressive changes have occurred undoubtedly contributes to the formation of cysts within the gland. The present findings indicate that iodide-deficiency alters the structure and function of mammary gland alveolar cells and makes them highly sensitive to stimulation by estradiol.