Extrathyroidal Benefits of Iodine

American Physicians and Surgeons Volume 11 Number 4 Winter 2006

http://www.jpands.org/vol11no4/millerd.pdf

ABSTRACT

In addition to being an essential element in thyroid hormones, iodine has many biological functions. The recommended dietary intake of 100.150 mcg is perhaps 100 times too low. Potential benefits of higher amounts include enhancement of immune function and reducing the incidence of breast cancer. Older studies of therapeutic benefits, particularly with respect to fibrocystic breast disease, need to be updated and expanded. Most physicians and surgeons view iodine from the narrow perspective of its use as an antiseptic that disinfects drinking water and prevents surgical wound infections, and its presence in thyroxine (T4) and triiodothyronine (T3). They consider iodine’s sole function in the body is to be organically bound to the phenyl ring of tyrosine in thyroid hormones. The thyroid gland needs only a trace amount of iodine, 70 mcg/day, to synthesize the requisite amounts of T4 and T3 used to regulate metabolism and ensure normal growth and development Everyone agrees that a lack of iodine in the diet causes a spectrum of disorders that includes, in increasing order of severity, goiter and hypothyroidism, mental retardation, and cretinism. In an effort to prevent these iodine deficiency disorders, which the World Health Organization estimates afflict 30 percent of the world’s population, health policymakers all subscribe to the same reference daily intake (RDI) for this element. First proposed in 1980, the RDI (formerly called the recommended dietary allowance) for iodine is 100.150 mcg/day, an amount considered sufficient to meet the requirements of nearly all, 97.98 percent of healthy individuals. Medical authorities consider an iodine intake greater than 750 mcg/day, an amount considerably more than that needed for production of thyroid hormones, to be .excessive.. But there is growing evidence that iodine provides important extrathyroidal benefits when taken in milligram amounts, in doses 100 times more than it’s RDI.

Iodine Consumption in Japan and the United States

Seaweed is a potent source of iodine, and the Japanese eat a lot of it. More than 95 percent of the iodine mainland Japanese consume comes from seaweed, which includes kelp (brown algae), nori sheets (red algae) with sushi, and chlorella (green algae). The concentration of iodine in these marine plants ranges from 0.5.8.0 mg/g. Terrestrial plants, in contrast, contain only trace amounts of iodine, 0.001 mg/g. In 1964, the Nutrition Section of Japan’s Bureau of Public Health found that people in Japan consumed a daily average of 4.5 g of seaweed with measured iodine content of 3.1 mg/g, or13.8 mg of iodine. According to bureau officials, seaweed consumption in Japan is now 14.5 g, providing 45 mg of iodine if its iodine content, which was not measured, has remained unchanged. Studies measuring urine concentration of iodine confirm that the Japanese consume iodine in milligram amounts. And researchers have determined that residents on the coast of Hokkaido eat a quantity of seaweed sufficient to provide a daily iodine intake of 200 mg/day.

Saltwater fish and shellfish contain iodine, but one would have to eat 15.25 pounds of fish to get 13mgof iodine.  The average daily intake of iodine in the U.S. is 240 mcg, well within the range that the International Council for the Control of Iodine Deficiency Disorders defines as an optimal iodine intake, 150 to 299 mcg/day. Though considered .iodine sufficient, this amount, 0.24 mg, is a small fraction of that consumed in Japan. Also, this is half the amount of iodine that Americans consumed 30 years ago, when iodine was used more widely in the dairy industry and as a dough conditioner in making bread. Now it is only added to table salt, and 45 percent of American households buy salt without iodine, which grocery stores also sell. And over the last 25 years those who do use iodized table salt have decreased their consumption of it by 65 percent. As a result, 15 percent of the U.S. adult female population, one in seven, suffers from iodine deficiency, as reflected in a urinary iodine concentration of less than 50 mcg/L. One in seven American women now also develops breast cancer during their lifetime (30 years ago it was 1 in 20). Although one cannot draw cause-and-effect conclusions by looking at single factors in the context of general health statistics, the incidence of breast cancer in the U.S. is the highest in the world, and in Japan, until recently, it was the lowest. Japanese women who emigrate from Japan or adopt a Western-style diet have a higher rate of breast cancer compared with those who eat seaweed. Life expectancy in Japan is 81.25 years, compared to 77.85 years in the U.S. Infant mortality rate in Japan is the lowest in the world, 3.5 deaths under age 1 per 1,000 live births, half the infant mortality rate in the United States. While no conclusions can be drawn from such figures concerning the benefits of iodine supplementation, they do suggest that iodine intake nearly 200 times greater than in the U.S. is unlikely to be toxic.

Iodine as Antioxidant

Oxygen breeds reactive oxygen species, which include superoxide anion, hydrogen peroxide, and hydroxyl radical. The hydroxyl radical wreaks havoc by reacting with lipids in cellular membranes, nucleotides in DNA, and tyrosine and sulfhydryl groups in proteins. In Laminariales, a species of kelp, Kupper et al. show how inorganic iodine functions as an antioxidant. It neutralizes hydrogen peroxide in a two-step process, converting it first to hypoiodous acid and then water, thereby preventing it from becoming a hydroxyl radical. These investigators also found that this alga absorbs increased amounts of iodine when placed under oxidative stress. Other investigators have shown that iodide is a specific scavenger of hydroxyl radicals, and that it, like vitamin C, increases the antioxidant status of human serum. Iodine defends brain cells in rats from lipid peroxidation, attaching to the double bonds of polyunsaturated fatty acids in cellular membranes, rendering them less susceptible to free radicals. As an interesting aside, cyanobacteria (blue-green algae), the most primitive organisms capable of photosynthesis, have an affinity for iodine, although it is present in seawater only in minute amounts, about 0.05 parts per million. Photosynthesis, with chlorophyll as a catalyst and sunlight as an energy source, converts six molecules of carbon dioxide and six molecules of water into one molecule of dextrose, with six molecules of oxygen as a waste product. In cyanobacteria, which are considered in large part the source of the oxygen in earth.s atmosphere, iodine probably serves as an antioxidant, while it is toxic to all other, nonphotosynthesizing bacteria. Indeed, iodine.s ability to neutralize reactive oxygen species apparently made photosynthesis possible. Algae, which also photosynthesize, are a dietary source of organic iodinated molecules and thus serve as a primitive thyroid gland for some invertebrates.