Do Cruciferous Vegetables Hurt the Thyroid?

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“Eat food, not too much, mostly plants.” -Michael Pollan

This is the advice most of us know to be true — that if we eat our veggies, and lots of them, we will be healthier… right?

I always thought so, until I was diagnosed with Hashimoto’s, an autoimmune condition affecting the thyroid. I read a lot of information about how people with thyroid problems should stop eating cruciferous vegetables, such as broccoli, cabbage, or cauliflower.

Unfortunately, these are some of my favorite vegetables! As I dug into the controversy, I found some sources claim that all cruciferous veggies should be avoided, while others say it’s okay to eat them if they’re cooked. I also read that it’s recommended to take a natural iodine supplement to support the thyroid when eating cruciferous veggies.

With all that conflicting information out there, I needed an answer to this question for myself.

I asked my doctor’s opinion on cruciferous vegetables, and his answer (combined with my own independent research) assured me that it’s perfectly safe to consume these vegetables regularly.

Here’s why:

What Are Cruciferous Vegetables?

First, a recap: cruciferous veggies are a hearty group belonging to the mustard family. They’re named for the Latin word Cruciferae that means “cross-bearing.” This term refers to the four petals of leaves on the plant that resemble a cross.

You might know that kale and broccoli are cruciferous veggies, but there are many more beyond those staples. Other cruciferous vegetables include:

  • Arugula
  • Bok choy
  • Brussels sprouts
  • Cabbage
  • Cauliflower
  • Collard greens
  • Horseradish
  • Mustard greens
  • Radishes
  • Rutabaga
  • Turnips
  • Watercress

These types of veggies are generally very healthy for you (read my post on broccoli sprouts if you need convincing), but you might have heard mixed things about eating them if you have a thyroid disorder.

Here’s a breakdown of why cruciferous vegetables are controversial, and why I think they’re safe to eat anyway.

Why Cruciferous Veggies Are Good For You

In my opinion, cruciferous vegetables represent some of the healthiest foods out there.

Most notably, leafy green veggies are protective against different types of cancer, including breast, lung, colorectal, and prostate cancers. This is all thanks to glucosinolates, a sulfur compound available only in cruciferous veggies. It’s what gives those veggies a pungent, slightly bitter taste.

Plus, cruciferous veggies are packed with health benefits. They’re an excellent source of minerals, like folate and fiber, and vitamins like C, E, and K. They also contain powerful phytochemicals that may help soothe chronic inflammation and reduce the risk of cardiovascular disease.

Too Much of a Good Thing?

The problem with cruciferous veggies is that they contain goitrogens, which are substances that affect the thyroid gland. Specifically, goitrogens mess with the thyroid’s ability to take in the essential mineral iodine. Your body needs it to produce thyroid hormone. If you don’t get enough iodine, it can lead to a bulge in the throat known as goiter.

This is especially problematic for people who already have an underactive thyroid and don’t want to slow it down further.

Cruciferous veggies aren’t the only foods to contain goitrogens. Other goitrogenic foods include:

  • Peaches
  • Peanuts
  • Red wine
  • Soy products
  • Strawberries
  • Sweet potatoes
  • Teas (green, white, oolong varieties in particular)

Peanuts and soy products aside, I wouldn’t go out of your way to avoid goitrogens. The health benefits of the food often far outweigh the negatives. This is because most people have an excess of iodine in their diets and not a deficit.

Why Eating Cruciferous Veggies Is Probably Safe

Despite the presence of goitrogens, I think the benefits of eating cruciferous veggies outweigh the negatives — even if you have thyroid problems.

That’s because you would have to eat enormous amounts of cruciferous vegetables to affect the thyroid. And I’m not sure many of us have the problem of overeating vegetables!

So far, there has only been one case study where too many cruciferous vegetables harmed the thyroid. In this case, an 88-year old woman developed hypothyroidism after eating two to three pounds of raw bok choy every day for several months.

So unless you’re eating several pounds of cruciferous vegetables daily, you are probably in the clear!

But What About Getting Enough Iodine?

Since cruciferous veggies mess with the thyroid’s ability to take in iodine, you might be concerned that your levels are too low. However, in today’s world it is pretty easy to have too much iodine, which can be just as detrimental to the thyroid (and was for me)!

This is especially problematic if there is a deficiency in selenium as well, as selenium can help mitigate the toxic effects of too much iodine in the thyroid.

My doctor Dr. Alan Christianson explained that if a person’s thyroid disorder is not caused by iodine deficiency, the iodine blocking properties of cruciferous vegetables are nothing to worry about (especially if the person is eating a nutrient-dense diet that contains natural sources of iodine and selenium). He estimates that over 90% of thyroid patients are clear of iodine deficiency problems, so cruciferous vegetables are almost always a non-issue.

On the other end of the spectrum, too much iodine can increase your risk of autoimmune disease, as evidenced by higher rates of autoimmune thyroid disease in Greece after iodine was added to the food supply.

In these cases, the mild iodine inhibition from cruciferous vegetables can actually be helpful for those with thyroid problems.

Plus, cruciferous vegetables may help the body produce glutathione, an antioxidant that can boost thyroid health and fight autoimmune disease.

So in other words, cruciferous veggies might actually be helpful for thyroid disease in many cases!

How I Minimize Goitrogens

If you plan on eating a large amount of cruciferous veggies, such as in the Wahls Protocol, and are concerned about any effects on your thyroid, there are easy ways to reduce the chance of any negative side effects.

1. Cook Your Veggies

If you’re still concerned about goitrogens, just be sure to cook or ferment your veggies instead of eating them raw. This will deactivate most of the goitrogens.

So for example if you drink green smoothies, consider blanching the spinach or kale ahead of time, then freeze until ready to blend.

2. Get Enough Iodine and Selenium

It also helps to make sure you’re getting enough iodine and selenium. Some great selenium-rich foods include:

As for iodine, you don’t need to stick to table salt to get your fill. Try these healthy iodine sources instead:

Personally, I eat a lot of green vegetables daily and consume about 75% of them cooked and only 25% raw. I also make sure that my diet contains natural sources of selenium.

Why I Don’t Recommend Supplementing With Iodine

You might be tempted to add an iodine supplement to your routine so you can safely eat more cruciferous veggies.

However, I don’t suggest trying one. A large intake of iodine can mess reduces the thyroid’s ability to produce hormones.  I learned this the hard way when my chiropractor recommended that I go the supplemental route. I immediately felt worse!

In most cases, it’s best to stick with natural and healthy sources of selenium and iodine while battling a thyroid problem. Pay attention to how your body adjusts to the extra intake of nutrients, and adjust your diet accordingly.

The Bottom Line

Cruciferous vegetables provide a variety of benefits, even (and especially) for those with thyroid disease. Of course, if you or your children are hypothyroid or battling autoimmune disease, you should work closely with a qualified doctor or functional medicine practitioner to find the best diet, medication, and lifestyle to fit your needs.

This article was medically reviewed by Dr. Terry Wahls, a clinical professor of medicine and clinical research and has published over 60 peer-reviewed scientific abstracts, posters, and papers. As always, this is not personal medical advice and we recommend that you talk with your doctor.

Do you suffer from a sluggish thyroid? Do you eat cruciferous veggies? Tell us about your experience in the comments below!

Sources:

  1. Chu, M., & Seltzer, T. F. (2010). Myxedema coma induced by ingestion of raw bok choy. New England Journal of Medicine, 362(20), 1945-1946.
  2. Drewnowski, A., & Gomez-Carneros, C. (2000). Bitter taste, phytonutrients, and the consumer: a review. The American journal of clinical nutrition, 72(6), 1424-1435.
  3. Higdon, J. V., Delage, B., Williams, D. E., & Dashwood, R. H. (2007). Cruciferous vegetables and human cancer risk: epidemiologic evidence and mechanistic basis. Pharmacological research, 55(3), 224-236.
  4. Liu, X., & Lv, K. (2013). Cruciferous vegetables intake is inversely associated with risk of breast cancer: a meta-analysis. The Breast, 22(3), 309-313.
  5. Talero, E., Avila-Roman, J., & Motilva, V. (2012). Chemoprevention with phytonutrients and microalgae products in chronic inflammation and colon cancer. Current Pharmaceutical Design, 18(26), 3939-3965.
  6. Xu, J., Liu, X. L., Yang, X. F., Guo, H. L., Zhao, L. N., & Sun, X. F. (2011). Supplemental selenium alleviates the toxic effects of excessive iodine on thyroid. Biological trace element research, 141(1-3), 110-118.
  7. Zois, C., Stavrou, I., Kalogera, C., Svarna, E., Dimoliatis, I., Seferiadis, K., & Tsatsoulis, A. (2003). High prevalence of autoimmune thyroiditis in schoolchildren after elimination of iodine deficiency in northwestern Greece. Thyroid, 13(5), 485-489.

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