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Thyroid Doc: Kale Risks ‘Theoretical’ But In Reality, Very Low To Minuscule

bittermelon/flickr

bittermelon/flickr

This post — “The Dark Side of Kale (And How To Eat Around It)” — went wildly viral this week, generating huge traffic and high passions over this once minor but now hotter-than-hot vegetable. Among the accusations from readers were charges that the post was “dubious and dangerous” and that I was, in effect “discouraging Americans from eating vegetables” (my children would disagree).

Still, for a medical reality check, I turned to a doctor who specializes in treating the thyroid.

(Before we get to him, for background, my post was inspired by an earlier piece in The New York Times on potential thyroid problems linked to kale and other cruciferous vegetables, called “Kale? Juicing. Trouble Ahead.” This article was troubling to me since I, too, am a devoted kale fan.)

OK, back to the thyroid expert, who points out that this debate is particularly timely since January is Thyroid Awareness Month.

Dr. Jeffrey Garber is chief of endocrinology at Harvard Vanguard Medical Associates, and lead author of the latest clinical practice guideline on hypothyroidism in adults. He agreed to answer a few more questions on the kale-thyroid connection.

I’d sum up Dr. Garber’s take on the whole kale issue pretty simply: It’s probably unwise to embrace a long-term, pound-a-day raw kale habit, but even if you do, you will, in all likelihood, be fine. (Especially if you live in the U.S., where iodine deficiency isn’t a huge problem, and if you don’t have a family history or predisposition to thyroid disorders.)

“If one isn’t a food faddist or predisposed to a thyroid problem (family history, prior diagnosis) the risks are very low,” Garber said. And, he adds, if you have any concerns at all, check in with your doctor for a simple thyroid test.

Here, lightly edited, is our Q&A:

RZ: In plain terms, what’s the connection between kale, a cruciferous vegetable, and thyroid function?

JG: There are many substances that can interfere with the way the thyroid functions. Goitrogens, as in those that promote goiter, make up one of these categories.
(There’s an enormous amount of interest in environmental goitrogens, like BPA and other substances, but that’s another story: We’re talking about dietary goitrogens here.)

When you get into the way goitrogens can affect the thyroid directly there are three general ways (and all relate to iodine, which is what thyroid hormone is made from):

1. the way the thyroid picks up the iodine;

2. the way the thyroid produces the hormone once the iodine is in the thyroid;

3. the way thyroid hormone is secreted into the bloodstream.

When you look at dietary goitrogens, they interfere with one or more of these three steps.

OK, so kale is one of these so-called “goitrogenic” foods, right?

Yes. Continue reading