Say it isn’t so!

Kale, the It vegetable of the past few years, is suddenly getting bashed in the media almost as much as Lindsay Lohan.  Can the leafy green, like the starlet, possibly be so in one minute and out the next?

The rumor: Kale—the wonder green juiced and eaten by countless number of health-conscious people—causes hypothyroidism (low thyroid hormone levels).  We wanted to get to the bottom of this rapidly developing Kale-Gate, so we went directly to the American Thyroid Association.

We spoke endocrinologist Angela M. Leung, MD She is a Clinical Assistant Professor of Medicine at UCLA David Geffen School of Medicine, Los Angeles, California and Chair of the Public Health Committee at the American Thyroid Association.  We asked her why kale, and other cruciferous vegetables, were suddenly getting such a bad rap?

Leung says it’s not sudden.  “The potential relationship between these vegetables (also termed goitrogens) and low thyroid hormone levels has long been hypothesized, but it has recently gained renewed attention due to the popularity of kale.”

Despite the interest over the years, Leung said there has been no large or definitive study linking kale consumption to thyroid function.   She said it’s been examined and discussed because kale “contains a substance that, in large amounts, can interfere with iodine nutrition.  Since adequate iodine intake is required for thyroid hormone production, kale thus has the potential, if consumed in high quantities, to result in hypothyroidism and/or an enlarged thyroid (goiter).”

Nutritionist Keri Gans, based in New York City, has looked into the greens controversy for worried patients.  We asked her what it would take to overdose on kale and impact the thyroid.

“According to the USDA,” she says,  “two to three cups of veggies, based on age and sex, is recommended daily. Most people aren’t even coming close to that.”  Could people possibly over do it?  “Anything is possible,” says Gans. “But it might take around 15 cups of kale to do so.”

Leung agrees, saying usual amounts of kale and other similar veggies like arugula, would have little impact, and in fact the positives—eating greens rich in nutrients—far “outweigh any potential negative side effects.”

The negative buzz has been mostly about raw kale.  “Supposedly, when cooking kale the goitrogen chemical is almost completely killed,” says Gans.  “It is this chemical that may inhibit absorption of dietary iodine which may exasperate symptoms of hypothyroidism.”

But from this discussion, does come a warning: “Since data are not available regarding the link between kale consumption and hypothyroidism,” says Leung, “ensuring adequate iodine is recommended.”  That means making sure you’re not only using the fancy new It salts, like sea, kosher, volcanic and others, but rather salt fortified with iodine.

“This is particularly important in women who may become pregnant, who are pregnant, or who are breastfeeding, since the developing infant is particularly susceptible to the effects of insufficient iodine and low thyroid hormone levels,” says Leung.


  1. American Thyroid Association
  2. Keri Gans