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Killer kale kicked in the keister for causing thyroid disease: Reality check

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It's a dark leafy green that has become the latest celebrity trend for weight loss, detoxing and juicing. Jennifer Aniston used it to prepare for her stripper role, while Beyonce reportedly fell in love with kale salad on her vegan diet cleanse. But now all those kale converts are questioning whether it could cause problems such as thyroid disease, reported Prevention magazine in a Jan. 19 newsletter questioning "Is Kale Causing My Health Problems?".

The kale calamity crisis resulted from a series of articles linking the beloved leafy green to hypothyroidism. The New York Times, for example, headlined an article "Kale? Juicing. Trouble Ahead.”

Advises Ashley Koff in Prevention: "If you are like many Americans experimenting with juicing and blending and raw kale salads, then you should be aware that in the raw form, cruciferous vegetable intake needs to be monitored related to thyroid hormone production, especially if you're taking medication."

Her suggestion: "Keep a food journal for a week and share it with your practitioner, who can check your levels via a simple blood test."

Lead author of the latest clinical practice guideline on hypothyroidism in adults, Dr. Jeffrey Garber is chief of endocrinology at Harvard Vanguard Medical Associates. He talked with NPR recently about the kale-thyroid connection.

"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," explained Dr. Garber.

Kale and other cruciferous vegetables labeled as goitrogens (examples include cabbage and cauliflower) can cause iodine-related problems. Moreover, that combined with deficiencies in selenium, iron and vitamin A can put you at risk for an underactive thyroid, according to Dr. Garber.

"Basically the goitrogens are challenges to the thyroid. But in the absence of iodine deficiency, substantial or prolonged ingestion of dietary goitrogens and lastly the absence of an underlying thyroid disorder, the risk in this country of having problems in this area are very, very low, almost miniscule. Again, that’s because the vast majority of people have adequate iodine levels to counteract the effect of goitrogens," he said.

But although Dr. Garber contends that kale isn't kicking you to the curb when it comes to thyroid health, the Linus Pauling Institute Micronutrient Information Center takes a scarier approach on killer kale in your kitchen.

The center reports that "very high intakes of cruciferous vegetables (such as kale, broccoli, and Brussels sprouts) can cause hypothyroidism. In one case, an 88-year-old woman developed severe hypothyroidism and coma after eating an estimated 1.0 to 1.5 kg a day of raw bok choy for several months."

The topic is particularly sensitive now because it's the month when those New Year's resolutions to achieve weight loss are still fresh. People with hypothyroidism often experience problems losing weight and may even gain as a result of their condition.

Teresa Fung, Sc.D., M.S., an adjunct professor of nutrition at the Harvard School of Public Health and a professor at Simmons College in Boston, confirmed the connection between kale and hypothyroidism but emphasized that it depends on the amount.

"It's the dose that makes a poison," Fung stated. "If people have hypothyroidism or they're taking thyroid medication, then they should check with their doctor. But even in this case, reasonable amounts shouldn't be a problem. Now, if people have a tall glass of kale juice every single day, then it gets into the unknown territory."

One issue with hypothyroidism: It can be challenging to diagnose without a visit to your doctor. Symptoms vary widely, including fatigue, dry skin, weight gain and muscle weakness, to pain and stiffness in the joints, thinning hair, depression and impaired memory.

Dr. Mehmet Oz has termed thyroid disease one of the trickiest to diagnose. Find out the symptoms and solutions as featured on his show recently by clicking here.

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