How to reduce goitrogens in cruciferous vegetables for thyroid health

Some people blame cruciferous vegetable as thyroid toxic as crucifers have goitrogenic compound. Goitrogenic compound negatively affect thyroid gland. How I will tell you. On the other hand cruciferous vegetables are unique and extremely nutritious. And missing cruciferous from your plate you are missing high valued nutrition dense foods. Do you really need to avoid crucifers? Or you are you believing in myth? What is the science? Let’s have a closer look. Going through we will know what is the science lying behind it. And also will know how to reduce goitrogens in cruciferous vegetable for thyroid health.

Your thyroid gland

The thyroid gland of endocrine system releases hormones that control metabolism—the way your body uses energy. It produces two important hormones as T4 (Thyroxine) and T3 (Triiodothyronine). The thyroid gland uses iodine from the foods you eat to produce T4. It is largely an inactive form. T4 converts to more active form T3 which involves in almost every physiological process in the body, including growth and development, metabolism, body temperature, cardiovascular, nervous system and reproductive health.(1) Multiple organs such as the liver, gut, skeletal muscle, brain, the thyroid gland itself etc involves in this process through deiodinase system (D1, D2, D3).

What is Goitrogen?

Goitro indicates swelling of enlarging thyroid gland. Goitrogens affect thyroid function by interfering thyroid hormone synthesis which results enlargement of the gland or goiter. Most cruciferous vegetables have goitrogenic compound with varying amount. But not only cruciferous vegetables many other foods like Bamboo shoots, soy product, Cassava, Corn, lima beans, millets, linseeds, peanuts, pears, pine nuts, strawberries can contain varying amount of goitrogens.(2) Toxins, heavy metal, pesticides etc can also negatively affect.

Apart from that a list of medications or drugs also have goitrogens or negatively affect thyroid health that includes some diuretic or high blood pressure lowering, Hypoglycemic agents, medication used in cancer therapy, some antibiotics, steroids, Antiseptic, expectorant, cholesterol reducing medicines and some others.(3,4,5,6,7,8) Use of such medication depends on physician consultancy and whether good part over-weighs bad part. Smoking also negatively affects thyroid hormone production.(9)

Iodine, More is not always better

Although trace element iodine is extremely essential for thyroid hormone synthesis excessive intake can be toxic to health. In fact excessive iodine is associated with increased risk of auto immune thyroiditis. Study on school children from Greece concluded that silent iodine prophylaxis has resulted in the elimination of iodine deficiency in Greece, and this has been accompanied by an increase in the prevalence of autoimmune thyroiditis.(10)

On the other hand selenium alleviates the toxic effects of excessive iodine intake on thyroid.(11) Foods containing high in selenium includes brazil nuts, pinto beans, sunflower seeds, wild caught salmon, lentils, eggs, mushrooms, spinach, oats, and more.

Cruciferous vegetables

Cruciferous vegetables contain dense source of nutrients loaded with vitamin C, vitamin E, vitamin K, folate, selenium, glucosinolates, flavonoids, polyphenols, and much more. Apart from that cruciferous veggies have many health beneficial effects like anti-inflammatory, antioxidant, antibacterial, antifungal, neuroprotective, glucose and lipid-lowering effects. Crucifers also improve cardiovascular health and prevent cancers.(12) In recent study researchers found compound in cruciferous vegetables that reawakens potent tumor suppressor.(13)

Goitrogens in Cruciferous vegetables(14)

Cruciferous vegetables contain a unique compound called glucosinolates, a large group of sulfur-containing glucosides. Apart from other classes cruciferous vegetables have two classes of glucosinolate family as progoitrin and indole glucosinolates with varying amount. In contrast, progoitrin degrades to goitrin and on the other hand indole glucosinolates degrades to thiocyanate. And goitrin as well as thiocyanate can interfere with iodine uptake and thus may decrease thyroid hormone production. However the potential adverse effects of goitrin and thiocyanates are based on their ability to inhibit iodine utilization by the thyroid.

And now we go through to what extent by which varying amount of these compound in different cruciferous vegetables can affect thyroid hormone production.

Indole glucosinolates or thiocyanate and thyroid hormone production

Apart from external source the thiocyanate ion also occurs naturally in humans. In various studies the naturally occurring thiocyanate concentration in human body found as 40–121 μM. On the other hand researchers found the maximum thiocyanate increase would be on the order of 10 μM from 100 g of fresh vegetable weight. They informed that since the amount is much less than the naturally occurring amount it is unlikely that thiocyanate arising from indole glucosinolates from normal serving sizes of common cruciferous vegetables would have significant adverse effects on thyroid function.

Progoitrin or goitrin and thyroid hormone production

Scientists reported 194 μmol of goitrin but not by 77 μmol of goitrin inhibited Iodine uptake to the thyroid. And found it is reasonable to conclude that a single serving of cruciferous vegetables with less than 70 μmol of progoitrin would be unlikely to result in decreased thyroid hormone production in humans.

The consumption of typical serving sizes of raw broccoli, Chinese cabbage, turnip, bok choy, broccoli rabe correspond to progoitrin and thiocyanate-generating indole glucosinolate exposures at concentrations far lower than those likely to impair thyroid function. In contrast 100g of fresh Chinese kale (119 μmol), Kale (Russian) (365.9 μmol), Kale (Siberian) (158.1 μmol), Kale(B. Napus- av. 176.6 -range 29–368) μmol, collard greens (314.16 μmol) has higher concentration of progoitrin than 70 μmol. Progoitrin concentrations of Brussels sprouts varies from 8.33 to 133 μmol which may be due to difference of environment and soil. You can see progoitrin concentrations per 100 g of fresh cruciferous vegetables with this link.

In fact in recent 2019 RCT study on 45 women with Broccoli sprout beverage consumption for 12 weeks found no effect either on thyroid hormone or thyroid autoimmunity. (15)

How to reduce goitrogens in cruciferous vegetables for thyroid health

Cooking. Yes cooking. Cooking of cruciferous vegetables breakdowns glucosinolate-myrosinase system, loss of enzymic cofactors and thus reduces goitrogens. In vitro boiling showed maximum reduction of gointrogens in vegetables like cabbage, cauliflower bamboo shoot and cassava high in goitrogens.(16, 17) However boiling leads to loss of nutrients also-keep in mind. Other form of cooking also reduces goitrogen and you need to remove the water to minimize the effect if that particular veggie containing high amount of goitrogens. As per research only at higher concentration goitrogen affects iodine uptake. Alternatively you can also offset this with supplementing iodine or foods with iodine.

In study inclusion of cooked Brussels sprouts (150 g daily for 4 weeks) into a normal diet of human volunteers had no effect on thyroid function as determined by measurement of thyrotrophic hormone. (18)

Know about how to choose right cooking oil for kitchen.

Other Concern

Oxalates and Kidney Stone

Cruciferous vegetables also contain oxalates. Oxalates bind with calcium as well as potassium and makes them less bio available.(19) In study major percentage of kidney stone contains calcium oxalate.(20) Soluble sources of oxalate appear to be better absorbed than insoluble sources. Fortunately again cooking reduces oxalates. Boiling markedly reduced soluble oxalate content by 30-87% followed by steaming 5-53%. (21) It is also reported to maximize the reduction of soluble oxalate during the cooking of high oxalate foods such as spinach and silver beet, a low fat milk cooking medium with neutral pH can be utilized.(22) You can remove the water from veggie containing high oxalates to minimize the effect.

However there are some serious issues with present cow milk. Know more about this with present cow milk.

Your Gut health and Oxalates

Oxalates can lead in development of kidney stone when it is absorbed through intestine. People with healthy gut absorb only a little amount of oxalates and majority passed out. However when there is increased intestinal permeability or leaky gut, absorption of oxalates become high through the paracellular “leak” pathway. (23,24) These oxalates then bind with circulating calcium and form calcium oxalate. This oxalate binded calcium then try to excrete through urinary system and also accumulates at kidney as kidney stone.

Human body lacks enzyme to breakdown oxalate. Gut bacteria degrades oxalates and thus helps to oxalate reduction. (25,26)Thus a healthy gut environment is necessary for not only oxalates excretion but also to maintain an overall gut health. In fact study found risk of developing IBS was 2.48 times higher in patients with kidney stone disease than in those without stone disease.(27) Many factors affect gut health negatively including toxins, chronic inflammation, food allergens including gluten, unhealthy foods, sugar, stress, bacterial imbalance, SIBO, medications like antibiotics, NASAIDs, acid suppressor and more. Moreover in 2018 study screening of more than 1000 marketed non antibiotic drugs or medicines found 24% of the drugs altered gut microbiota. (28) Also study found gastric by pass surgery had increased intestinal oxalates absorption. (29)

Bottom Line

According to researchers at Oregon State University, normal consumption cruciferous vegetable does not appear to increase the risk of hypothyroidism unless accompanied by iodine deficiency. Similarly, consumption of high amounts of cruciferous vegetables has been associated with increased thyroid cancer risk only in iodine-deficient areas. Even people with hypothyroidism or with family history can enjoy cooked cruciferous vegetables however in a controlled manner. Again more is always not better. An elderly woman in New York presented with the most severe form of hypothyroidism after ingesting up to 1.5 kg of raw bok choy daily for several months.(14) Goitrogenic compounds vary with vegetables to vegetables. Therefore individual with hypothyroidism more specifically with iodine deficiency should have control over vegetables with high progoitrin content. Look at the progoitrin part.

Apart from healthy diet other factors that take part in thyroid heath includes stress management, gut health, minimize toxins, liver health, vitamin D along with vitamin K2 etc. And if you have information about this I will be happy to hear from you.

Disclaimer: Information provided here are generalized information for 
educational purpose only,  not intended to provide one to one health 
consultation or replace practice of a qualified practitioner. Different 
people may have different health condition and may have different reaction 
to the same food. Hence it has been advised to consult with health care 
provider before application of any of above guidelines.
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