Kale and Biotin Can Interfere with Thyroid Function and Lab Reports

By Joan Haynes, NMD

Kale and Other Cruciferous Veggies

Kale is a cruciferous vegetable related to other well-known healthy veggies such as broccoli, Brussels sprouts, and cabbage. Cruciferous vegetables are unique in that they are rich sources of healthy, sulfur-containing compounds known as glucosinolates. Glucosinolates form a substance called goitrin that can suppress the function of the thyroid gland by interfering with iodine uptake, which can, as a result, cause poor function and enlargement of the thyroid gland.

Cooking Destroys Glucosinolates

Once cooked, cruciferous foods lose up to 80% of their goitrogenic (iodine interfering) chemicals, so they no longer block the uptake of iodine. Studies show steaming for 3 minutes ensures the bioavailability of helpful nutrients we want from these vegetables but destroys the goitrogenic effect. Blanching (cooking the vegetable quickly in boiling water) is extra effective because the glucoinolates float off into the water. I strongly recommend cooked, daily cruciferous veggies with some occasional raw ones weekly too.

Green Smoothie Danger

Many people are under the mistaken impression that a daily raw kale smoothie is a healthy choice. Certainly, the occasional one is fine, but its when people are having daily, massive amounts of kale that we see interference of thyroid function. Especially juicing of kale in large amounts and on a very frequent bases is not recommended either, especially for people who may already be iodine deficient such as vegetarians and vegans.

Biotin – A Culprit in Thyroid Testing

Biotin is a B vitamin, and the Institute of Medicine recommends a daily intake of 30 mcg. That’s micrograms. But many patients take “hair, skin, and nails” supplements that contain milligram doses – that’s a thousand fold increase. When patients take megadoses of biotin, it can cause falsely high and falsely low results in a variety of laboratory tests, including thyroid tests. Inaccurate test results can cause misdiagnoses and even mistreatment. Be sure to tell your health care providers about all the nutrients you are taking when you are getting lab work.