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Ask the RN: Kerri Zemko

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March 1, 2013

Kerri Zemko, R.N., B.S.N., O.C.N., is an oncology research nurse and PCRM Food for Life Instructor. Visit her on Facebook for more information on her upcoming Food For Life classes. Do you have a health related question? Email us at

Q: I have heard that although cruciferous vegetable (Broccoli, cauliflower, bok choy, mustard greens, collards, brussel sprouts, etc.) have many cancer-fighting qualities, those with thyroid issues should limit or even avoid these vegetables. Is this true?

A: That is a great question. The thyroid gland assembles T3 and T4 from dietary iodine and the non-essential amino acid tyrosine (deficiency of which is almost unheard of, from what I can see). In most parts of the world and in much of history, the primary cause of hypothyroidism (inadequate levels of T4) has been inadequate intake of iodine. Some patients with hypothyroidism develop a goiter, an enlargement of the thyroid gland that appears as a bulge in the neck. (A very severe, life-threatening, are rare event due to hypothyroidism is called myxedema coma, but be aware that the terms myxedema and coma each have other, completely different, clinical meanings, as well.)

The practice of iodizing table salt, which started in Michigan, where prevalence of goiter was high, has reduced the rate of iodine-deficiency hypothyroidism dramatically. If iodine deficiency can somehow be ruled out, other causes are intrinsic dysfunction of the thyroid gland (primary hypothyroidism), failure of the pituitary gland to secrete enough thyroid stimulating hormone (secondary) and a malfunction in the hypothalamus (tertiary hypothyroidism). Hashimoto’s disease, an autoimmune condition, is now the most common cause of hypothyroidism in the United States. For some time, most sea salt available for purchase was NOT iodized. It’s possible that people who chose sea salt over iodized table salt may have reduced iodine levels. Other contributing causes of thyroid insufficiency can be undiagnosed celiac disease (true gluten intolerance) and insufficient selenium. So choose iodized (sea) salt when you use it, eat one Brazil nut per day for your whole day’s worth of selenium, and consider a workup for celiac disease, or a gluten elimination diet, if these may be an issue for you. Sea vegetables are a fantastic source of dietary iodine (if, like me, you don’t like the idea of intentionally adding salt), and choose any variety except hijiki.

Cruciferous vegetables HAVE been linked with hypothyroidism through a metabolic process resulting in a compound that competes with iodine in the thyroid gland, but it seems that the problem may only be related to very, very high intake of these veggies, and probably only in their raw state. Most of the sources I’ve found on this association all refer to the same case study, so by no means is this a common problem.

Michael Greger has a couple excellent videos on the topic and reaches the conclusion that you’d have to be eating at least 4 cups of raw cruciferous veggies, or at least 10-15 cups of cooked, to potentially run into a problem. Search “goitrogens” or “thyroid” at to find his videos. This is another good source of information.

I hope this answered the question and I’d be happy to discuss further if not!

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