Some early studies correlate low iodine levels with an increased risk of breast cancer. These low levels usually correlate with low selenium levels as well, more classically associated with cancer. A higher incidence of breast cancer has been shown to occur in the goiter belt, whereas areas with high soil levels of iodine and selenium show a lower incidence.
Requirements: The RDA for iodine in adults is 150 mcg. The amount necessary to prevent goiter is about 1 mcg./kg.-that is, about 50-75 mcg. for most adults. Average intake from diet ranges from 65 mcg. to about 650 mcg. Much of that may come from iodized salt, which is not highly recommended; however, it is very difficult to avoid salt completely in our culture because it is added to so many prepared foods and by restaurants and mothers everywhere. A 6-ounce portion of ocean fish contains about 500 mcg. of iodine, more than is contained in one teaspoon of salt but without the extra 2 grams of sodium. Ideally, we can meet our iodine requirements by eating seafood, seaweed, and vegetables grown in iodine-rich soil. A typical mineral or complete vitamin supplement will contain the RDA, 150 mcg., of iodine per day. More iodine is needed during pregnancy and lactation. People on low-salt diets may need supplemental iodine.