Joan Valentine Blog

The Emerging Role of Iodine in Breast Health

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From the October 2011 issue of Life Extension

Iodine deficiency is rapidly emerging as a major risk factor for breast cancer.

Human breast tissue and breast milk contain higher concentrations of iodine than the thyroid gland itself, which contains just 30% of the body’s iodine stores. Breast tissue is rich in the same iodine-transporting proteins used by the thyroid gland to take up iodine from the blood.18,38 The evolutionary reasons for this are clear: iodine is essential to the developing newborn brain, so the mother’s body must have a direct means of supplying iodine to the nursing infant.

Iodine plays an important role in the health of women’s breast tissue. In the presence of chemicals and enzymes found in breast tissue, iodine has been shown to exert a powerful antioxidant effect equivalent to vitamin C. Iodine-deficient breast tissue exhibits chemical markers of elevated lipid peroxidation, one of the earliest factors in cancer development.

Iodine-deficient breast tissue also shows alterations in DNA and increases in estrogen receptor proteins.40 Coupled with iodine deficiency-induced increases in circulating estrogen levels, these changes can substantially increase the risk of breast cancer in women with low iodine levels. Iodine also helps regulate levels of the stress hormone cortisol and contributes to normal immune function. Abnormal cortisol levels and deficient immune function are significant contributors to the risks of breast cancer; women with fibrocystic breast disease may also suffer from elevated cortisol levels.

Taken together, these biological factors explain the well-known link between iodine deficiency and thyroid disease, thyroid cancer, and breast cancer, all of which predominate in postmenopausal women.The link between iodine consumption and breast cancer is most evident when you compare the Japanese and Western diets against cancer incidence.

Japanese women consume a diet high in iodine-rich seaweed, which provides them with an iodine intake 25 times higher than the average American woman’s. Japanese women also have breast cancer rates roughly one-third of those found in American women, a difference that disappears in Japanese women who immigrate to the US, where they consume considerably less seaweed.

Studies of iodine therapy for breast cancer prevention are encouraging. Continuous iodine given to cancer-prone rats cut mammary tumor rates nearly 2.5-fold. Breast cancer cells avidly absorb iodine, which in turn suppresses tumor growth and causes cancer cell death. Added dietary iodine reduces the size of both benign and malignant breast tumors, an effect credited in part to iodine’s direct reduction of lipid peroxidation levels. Although the doses of iodine used in these studies are substantial, equivalent to 5,000 mcg daily, no toxic effects of iodine were observed, either on thyroid function or in other tissues.

Further benefits may be obtained by supplementing with selenium in addition to iodine; selenium is an essential cofactor in the enzymes used in thyroid and breast tissue to make optimal use of dietary iodine.In addition to its obvious role in preventing breast cancer, increased iodine intake may be important in mitigating another common, if less lethal, breast disorder—fibrocystic breast disease or FBD.

While harmless, fibrocystic breast disease is extremely common. It is found in at least 9% of all women who undergo biopsies, though the actual rate is probably much higher.18,59 Animal studies have shown that fibrocystic breast disease can be induced by depriving breast tissue of iodine.11,40,60 These changes can be reversed by iodine doses equivalent to 5,000 mcg per day in humans.

Women with fibrocystic breast disease obtain substantial relief from oral administration of iodine at doses of 3,000-6,000 mcg, with 65% achieving improvements according to their own and their physicians’ assessments.62 In those studies, only 33% of placebo recipients reported any benefit. No side effects were detected at any of the doses used.

It is becoming increasingly clear that iodine deficiency interferes with optimum breast health, and intake of levels far higher than the recommended dietary allowance of 150-290 mcg is required to achieve benefits. Daily amounts of 3,000-6,000 mcg may help relieve the symptoms of fibrocystic breast disease.

Iodine Protects Against Stomach Cancer

The thyroid gland, breast tissue, and portions of the digestive tract share similarities in that all of them contain a rich concentration of iodine. Stomach lining cells in particular concentrate iodine, capitalizing on its antioxidant effects.

This has led medical researchers to investigate whether iodine deficiency plays a role in cancers of the digestive tract. They found that people living in iodine-deficient areas of the world are not only prone to iodine-deficiency goiters, but also have higher rates of stomach cancers. Stomach cancer patients in a landlocked area of Iran were 2.5 times as likely to have severe iodine deficiency than control patients.

Gastric cancer is the most common cancer in parts of northeastern Turkey where iodine deficiency is common, and iodine levels in gastric cancer tissue were markedly lower than those in surrounding healthy tissue.

Increased iodine intake has been strongly correlated with a reduction in stomach cancer rates in recent years.


Iodine is critical to healthy thyroid function. Its deficiency can cause weight gain, low energy, depression, cardiovascular disease, cognitive decline, and a variety of cancers. Yet rates of iodine deficiency have reached epidemic levels, increasing fourfold over the past 40 years. A startling 74% of normal, “healthy” adults may no longer be consuming sufficient quantities.Recent scientific analysis reveals that many commercial table salt brands now contain inadequate amounts of iodine. Emerging evidence points to the severe impact of low iodine on a wide range of health issues, including increased risks of breast cancer and fibrocystic breast diseases.

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