International Council for the Control of Iodine Deficiency Disorders

There is growing evidence that Americans would have better health and a lower incidence of cancer and fibrocystic disease of the breast if they consumed more iodine. A decrease in iodine intake coupled with an increased consumption of competing halogens, fluoride and bromide, has created an epidemic of iodine deficiency in America.

Health comparisons between the two countries are disturbing. The incidence of breast cancer in the U.S. is the highest in the world, and in Japan, until recently, the lowest. Japanese women who emigrate from Japan or adopt a Western style diet have a higher rate of breast cancer compared with those that consume seaweed. Life expectancy in the U.S. is 77.85 years, 48th in 226 countries surveyed. It is 81.25 years in Japan

People in the U.S. consume an average 240 micrograms (µg) of iodine a day. In contrast, people in Japan consume more than 12 milligrams (mg) of iodine a day (12,000 µg), a 50-fold greater amount. They eat seaweed, which include brown algae (kelp), red algae (nori sheets, with sushi), and green algae (chlorella). Compared to terrestrial plants, which contain only trace amounts of iodine (0.001 mg/gm), these marine plants have high concentrations of this nutrient (0.5–8.0 mg/gm).
 

An Important Note: The researchers were defining overt hypothyroidism as a TSH above 4.8, with elevated Free T4 levels. Subclinical hypothyroidism was defined as a TSH above 4.8, with normal range Free T4 levels. The American Association of Clinical Endocrinologists, along with the National Academy of Clinical Biochemistry, recommended in late 2002/early 2003 that the TSH normal range be narrowed substantially to .3 to 3.0. So the point at which someone would be considered overtly hypothyroid might be different, based on

The most visible consequence of iodine deficiency is goiter. This word means "an enlarged thyroid." The process begins as an adaptation in which the thyroid is more active in its attempts to make enough thyroid hormone for the body's needs, despite the limited supply of raw material (iodine), much as a muscle gets bigger when it has to do more work. If this adaptation is successful and the iodine deficiency is not too severe, the person may escape with only an enlarged thyroid and no other apparent damage from the iodine deficiency. Older individuals with goiters may develop nodules (lumps) in their thyroids, and sometimes these can begin making too much thyroid hormone when suddenly exposed to iodine. This result occurs because these nodules are independent of usual controls; they make thyroid hormone at their own rate, and may over-produce it when given more iodine. Also, the nodular goiters in iodine deficiency have an increased rate of one type of thyroid cancer, called "follicular cancer." Goiters can sometimes enlarge enough to produce compression of other neck structures and may need surgical removal for that reason.

In addition to these effects on the individual, iodine deficiency has adverse consequences for the community. The mental retardation can cover a wide range, from mild blunting of intellect to cretinism, and a large part of the population may have some intellectual impairment. The mean IQ of the deficient community is decreased by about 13.5 IQ points, according to one review. Individuals in these communities have lower educability and lower economic productivity, and the output of the whole community suffers. Dramatic improvement typically occurs after appropriate addition of iodine.

People with a tendency towards so-called autoimmune thyroid diseases, such as Graves' disease or Hashimoto's thyroiditis, or who have family members with these problems, may be more sensitive to iodine. In fact, high iodine intakes in a population are associated with an increased incidence of these autoimmune thyroid diseases. Also, high levels of iodine in the population may increase the incidence of papillary thyroid cancer, although this is not well established. Fortunately, papillary thyroid cancer is usually a mild form of cancer and rarely causes death.

Iodine also induces apoptosis, programmed cell death. This process is essential to growth and development (fingers form in the fetus by apoptosis of the tissue between them) and for destroying cells that represent a threat to the integrity of the organism, like cancer cells and cells infected with viruses. Human lung cancer cells with genes spliced into them that enhance iodine uptake and utilization undergo apoptosis and shrink when given iodine, both when grown in vitro outside the body and implanted in mice. Its anti-cancer function may well prove to be iodine’s most important extrathyroidal benefit.