Iodine is most known for its relationship to the production of thyroid hormones. Not well known is that iodine also functions as a key antioxidant that protects cell membrane fatty acids from free radical attack. This is important for all cell membranes, however, in the context of disease risk, it is especially important for protection against breast cancer and prostate cancer (1,2).
The Japanese population consumes between 1000-3000 micrograms (mcg) per day (1), which is derived largely from seaweed and less from fish. It turns out that seaweed and fish are natural sources of both omega-3 fatty acids and iodine, which is one of the reasons why a traditional Japanese diet is so healthy and associated with minimal disease risk. Iodine naturally complexes with cell membrane fatty acids to create what is called an iodolipid, which is resistant to free radical attack compared to fatty acids without iodine (2).
In the United States, the upper limit recommendation for iodine is only 1100 mcg per day, with most Americans taking in between 135-340 mcg per day. The 1000-3000 mcg level consumed by the Japanese is a clear sign that people can tolerate more than 1100 mcg without concerns. This amount of iodine is likely to be problematic for only people with hypothyroidism caused by Hashimoto’s disease (1). Be aware that some people with Hashimoto’s cannot tolerate any iodine supplementation.
The National Institutes of Health has an Office of Dietary Supplements that published a Fact Sheet about iodine (3). It describes a study wherein researchers randomly assigned 111 women (18–50 years of age) with fibrosis and a history of breast pain to receive tablets containing 0 mcg, 1,500 mcg, 3,000 mcg, or 6,000 mcg of iodine per day. After 5 months of treatment, women receiving doses of 3,000 or 6,000 mcg iodine had a significant decrease in breast pain, tenderness, and nodularity compared with those receiving placebo or 1,500 mcg iodine. The researchers also reported a dose-dependent reduction in self-assessed pain. None of the doses was associated with major adverse events or changes in thyroid function test results. As the upper limit in the United States is only 1100 mcg, this NIH Fact Sheet recommends that doses of 1,500-6000 mcg per day should only be used under the guidance of a physician (3).
Fish oil supplements do not contain iodine because the distillation process that concentrates and purifies the oil serves to eliminate pollutants, heavy metals like mercury, and iodine. Taking supplemental iodine appears to be a good choice for most people, especially for those who take supplemental fish oil.
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