Iodine is required by the body to make thyroid hormones. A recent study of vegans estimated that only about 40% of the daily requirement for iodine was commonly met on a vegetarian or vegan diet. Another study concluded that 80% of vegans, 25% of vegetarians, and 9% of conventional eaters are iodine-deficient. Most plant foods are low in iodine due to soil depletion. Kelp, a sea vegetable, is a good source of iodine, but is not commonly eaten on a regular basis and may actually provide excessive amounts of iodine. The chief source of iodine in the typical American diet is iodized salt. Since salt should be avoided for good health, it is important to supplement with iodine to maintain adequacy.
Claim: soy contains goitrogens that interfere with thyroid function. It is true that soy contains goitrogens, as do many other foods such as cruciferous vegetables (cabbage, cauliflower, broccoli and Brussels sprouts), sweet potatoes, lima beans, flaxseeds and millet. However, these foods have been implicated in thyroid dysfunction only when iodine status is poor. Soy does not cause thyroid problems in healthy, well-nourished people who are not deficient in iodine. However, vegetarians who do not insure a reliable source of iodine could increase their risk of thyroid problems if they eat a lot of soy and/or other foods rich in goitrogens (the main sources of iodine in a mixed diet are iodized salt, dairy products and fish). The answer is not to avoid soy or cruciferous vegetables, but to get enough iodine.
- Avoid iodized salt because of excess sodium
- Avoid kombu, kelp, paddle weed and hijiki seaweeds because they contain too much iodine and can lead to iodine toxicity (especially avoid hijiki because of its arsenic content)
- Develop a taste for other seaweeds like nori and dulse that contain safe amounts of iodine
- Consider taking a iodine supplement if you avoid iodized (table) salt
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Avoiding Iodine Deficiency by Dr. Michael Greger, MD
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Too much iodine can be as bad as too little by Dr. Michael Greger, MD
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Safe supplement that includes iodine