Role of iodine in evolution and carcinogenesis of thyroid, breast and stomach.

The authors have hypothesized that dietary iodine (deficiency or excess) is associated with the development of some gastric and mammary cancers, as it is well-known for thyroid cancer. They report a short review of their own work and of the general literature on this correlation and on the antioxidant function of iodide in stomach, breast and thyroid. Thyroid cells phylogenetically derived from primitive iodide-concentrating gastroenteric cells which, during evolution, migrated and specialized in uptake and storage of iodine, also in order to adapt the organisms from iodine-rich sea to iodine-deficient land. Mammary cells also derived from primitive iodide-concentrating ectoderm. Stomach, breast and thyroid share an important iodide-concentrating ability and an efficient peroxidase activity, which transfers electrons from iodides to the oxygen of hydrogen peroxide and so protects the cells from damage caused by lipid peroxidation. The authors suggest that iodide might have an ancestral antioxidant function in all iodide-concentrating cells from primitive Algae to more recent Vertebrates. In Italy, gastric cancer is more frequent in farmers and in iodine-deficient populations, living in mountainous and hilly areas, than in fishermen. In the last two decades, Italian decrease of gastric cancer seems to be correlated more to the higher dietary consumption of iodine-rich fish rather than to consumption of fruit and vegetables, which indeed has decreased in Italy.