Guide to Dietary Supplements and Thyroid Disease

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Dietary and herbal supplements are frequently used by people with thyroid disease, but there are many things to consider before taking these products. Some may have benefits specifically for those who have hypothyroidism. On the other hand, some products may interfere with the absorption of thyroid hormones, interfere with testing, or pose other dangers. While the following discussion is not comprehensive, we will discuss some of the important supplements that may either help or hinder your health with thyroid disease, and questions you should ask before you take them.

Understanding Dietary Supplements

Before talking about supplements that may be good or bad for people with thyroid disease, it's important to briefly mention a few things about dietary or herbal supplements. In the United States, dietary supplements aren't regulated to the same degree as prescription medications. This means that you may or may not receive the dose of an ingredient listed on the label. Some supplements that are safe in general, could be unsafe for some people. For example, there are several products that can thin the blood and could increase bleeding for people having surgery. Potential drug interactions must also be considered, as some supplements may not pose a danger alone, but could when used in combination with other drugs or supplements.

Many physicians believe that you should carefully weigh the benefits and risks of taking any dietary supplement just as you would a prescription medication.

Supplements Commonly Used by Thyroid Patients

As with many conditions, there are a number of supplements that are commonly recommended as being "healthy" for people with thyroid disease. That said, even supplements that may have benefits for some people could have potential risks for others. It's best to speak to your doctor before adding these or any other options to your regimen.


Perhaps the most common dietary supplement used is multivitamins (MVIs). While MVIs are recommended (and thought to make a difference) for women who are pregnant, most vitamins and minerals are ideally obtained through a healthy diet alone. Exceptions may include vitamin D, vitamin B12, and a few more in certain situations.

There are several reasons why getting vitamins through a healthy diet instead of supplements is optimal. Many studies looking at the benefits of fruits and vegetables have failed to see the same benefits when the vitamins are obtained in supplement form, and in some cases, supplements may actually increase health risks. For example, a diet rich in beta-carotene from dietary sources has been linked to a significantly reduced risk of lung cancer, whereas a large study following people who took beta-carotene supplements actually found an increased risk of the disease.

There are also potentially harmful nutrients in multivitamins. For example, excess iron intake (especially in men and women who are no longer menstruating) can build up in the body causing iron overload.

Vitamin D

Low vitamin D levels are associated with an increased risk of developing autoimmune thyroid diseases such as Hashimoto's thyroiditis and Grave's disease. Yet, even though low levels have been linked to many diseases, including several cancers, the benefit of supplementation is not always clear.

Unlike most vitamins, it's difficult to get enough vitamin D from food. Sun exposure is a leading source of vitamin D as well, but can be significantly reduced in northern climates, when time outdoors is limited, or with the use of sunscreen. Fortunately, a simple blood test can help you know whether you are deficient or not.

A 2018 Indian study suggests that vitamin D supplements may be helpful for those with thyroid diseases. In this study, the supplements improved TSH levels in people with hypothyroidism, as well as thyroid autoantibodies in people with autoimmune thyroiditis.

Note that taking excess vitamin D can lead to side effects such as painful kidney stones.

Vitamin B12

Vitamin B12 deficiency has been linked with an increased risk of stroke, even in young people, and under-treated hypothyroidism is associated with an elevated risk as well. Vitamin B12 is obtained from meat and animal products, but even with adequate intake, poor absorption due to age or digestive conditions can result in low levels. Vitamin B12 deficiency can lead to anemia and other conditions that can mimic many of the symptoms of hypothyroidism.

The drug metformin may reduce B12 levels, and deficiency may occur even with short-term use. The drug is often used for insulin resistance, and is sometimes prescribed to aid in weight loss for people with thyroid disorders.

Omega-3 Fatty Acid Supplements

Omega-3 fatty acids are being increasingly recommended in the diet for their anti-inflammatory properties. Ideally, fish oil can be obtained by eating fatty fish (such as salmon, herring, tuna, and mackerel) at least two to three times per week. That said, many people do not like eating fish, especially this often.

Fish oil supplements, especially eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are thought to be particularly beneficial among people with autoimmune thyroid disease for both their anti-inflammatory and immune modulating properties. If you choose to use a supplement, buying a good product is important to avoid excess mercury levels. Common side effects include burping with a fishy flavor, and stomach upset. Fish oil can also increase bleeding time, so should be avoided for people on blood thinners or with bleeding problems.

Plant-based omega-3 fatty acid supplements are also available, but are not usually absorbed as well as fish oil.

Conjugated Linoleic Acid (CLA)

Conjugated linoleic acid is often recommended for people with thyroid disease who are struggling with trying to lose weight. There is some evidence that these supplements may contribute to modest weight loss by mobilizing fat stores in the body. These supplements can cause gas and digestive upset in some people. If you are trying to lose weight with hypothyroidism, ask your doctor for her recommendations.


There has been significant controversy over iodine supplements and thyroid health, including the use of kelp supplements (kelp is high in iodine). Iodine deficiency, however, is extremely rare in the United States, and these supplements may not only fail to help, but could, potentially, make things worse. The American Thyroid Association suggests avoiding daily consumption of dietary supplements that have more than 500 micrograms of iodine.


Selenium is important in thyroid hormone metabolism and may be used alone or as a component of a multivitamin. It's important to note, however, that the "therapeutic window" for selenium is very narrow, in other words, even small excesses may be toxic. That said, for people with thyroid disease who are not getting an inadequate intake, there may be some benefits. A 2018 study found that selenium supplementation may reduce anti-thyroperoxidase antibody levels in people with autoimmune hypothyroidism. In those with Grave's disease, improvements were noted in thyroid antibodies as well as quality of life.


Zinc is needed for the synthesis of thyroid hormones in the body, and a deficiency can lead to hypothyroidism as well as other autoimmune diseases. There are relatively few studies looking at the effect of zinc supplementation, though a 2018 study found these supplements to have some benefit for overweight and obese women with hypothyroidism.

Thiamine (Vitamin B1)

Hypothyroidism (and other autoimmune disorders) can lead to reduced absorption of thiamine, even with adequate intake. There is some evidence that thiamine supplements may reduce fatigue in people with Hashimoto's thyroiditis.

Supplements That Can Effect Thyroid Medications and Testing

Virtually any supplement or over-the-counter medication may interact (result in decreased absorption) with levothyroxine if taken within an hour of dosing, though some supplements may cause problems even if taken later on, or interact in other ways.

Calcium and Iron

Calcium and iron supplements should be taken at least three hours to four hours after levothyroxine, but other associations between calcium supplementation and thyroid disease have been noted as well. A 2016 study noted an increased risk of large papillary thyroid cancer with short-term (5 years or less) calcium supplementation. In contrast, people who used long-term calcium supplementation (defined as greater than 10 years) were found to have a lower risk of papillary microcarcinoma of the thyroid.

"Green Food" Supplements

Many "green food" supplements contain large amounts of cruciferous vegetables, such as broccoli and spinach. Many of these otherwise healthy foods contain goitrogens, substances that have an anti-thyroid effect in the body. People who have hypothyroidism do not need to avoid these healthy foods, but spacing them out in the diet and avoiding supplements with concentrated amounts is wise.


Biotin alone or as a component of B complex vitamins can interfere with the immunoassay used to determine TSH levels. (TSH may appear to be lower than it actually is.) Biotin is a common ingredient in many supplements designed to improve hair, skin, and nails.

Supplements to Avoid

There are some supplements that are best avoided altogether by people living with thyroid disease. This is not an exhaustive list, but some of these include:

Ashwagandha and Bladderwrack

Some herbal preparations may include ingredients such as ashwagandha and bladderwrack. There’s no credible evidence to show these herbs will help a thyroid problem, but they may interact with your thyroid medication. Bladderwrack may also have dangerously high levels of iodine.

"Thyroid Support" Supplements

There are a number of supplements that may be labeled as providing "thyroid support," "adrenal support" or may claim to be "thyroid boosters." The ingredients in these products vary, but in addition to a mix of vitamins, minerals, and herbs, may contain thyroid hormone and/or adrenal steroids.

These supplements should absolutely not be used instead of prescription thyroid medications, but may cause problems when used with thyroid hormone replacement therapy as well. When used along with prescription thyroid hormone replacement, over-the-counter thyroid supplements increase the risk of overmedication (hyperthyroidism). Hyperthyroidism, in turn, increases the risk of osteoporosis, atrial fibrillation (an abnormal heart rhythm that can lead to strokes or heart failure), and more.

A 2013 study looking at 10 commercially available thyroid support products found that the majority of supplements contained clinically significant amounts of T3 and T4. In fact, in some cases, the doses exceed amounts typically prescribed to treat hypothyroidism. A 2016 study, found that the amount of T3 in some supplements was high enough to cause thyrotoxicosis (thyroid storm).

Bovine Thyroid Extracts

Bovine thyroid extracts are made from the adrenal glands of cows and sold as dietary supplements. These should not be confused with thyroid hormones. In addition to the risks of undertreated or overtreated hypothyroidism noted above, bovine extracts pose a slight risk of being exposed to bovine spongiform encephalopathy (BSE) or "mad cow disease,” if the health of the animals used for the extracts isn’t known.

Imported Supplements

In 2004, the FDA prohibited the sale of dietary supplements containing the stimulant ephedra, but some imported supplements and teas continue to contain this ingredient. Often marketed as a supplement to aid in weight loss and energy, the dangers of ephedra outweigh any benefits. Adverse effects, such as high blood pressure, strokes, seizures, and death, have occurred even in people who are young and healthy.

Imported supplements may also contain other ingredients that are not considered safe by the FDA, some of which may be listed under names you're unfamiliar with.

Questions to Ask About Any Supplement

If you are considering taking any vitamin, mineral, or dietary supplement, it's important to talk to your doctor and weigh the potential risks and benefits. Questions you may wish to ask include:

  • What is the possible benefit of this supplement? Have any scientific studies documented this finding, or is it hearsay?
  • What are the potential side effects? What symptoms would alert you to a possible adverse effect?
  • How may the supplement interfere with other medications, including the absorption of levothyroxine?
  • Should the supplement be taken with or without food?
  • Will you need to have more frequent thyroid testing if you choose to take the supplement? How often?

A Word From Verywell

The reality is that dietary supplements and over-the-counter medications have bioactive components, and the potential risks and benefits of these products should be evaluated just like any prescription medication. In addition, some of these supplements can interact with other drugs or supplements, including thyroid hormones.

While some supplements may be beneficial in general for people with thyroid disease, everybody is different. A medication that may be helpful for one person may be detrimental for another. Talk to your doctor before taking any of these products. If your doctor is unfamiliar with supplements or herbal therapies, talking with a naturopathic is another option (but the information should then be discussed with your thyroid-treating physician). Note that "natural" and "herbal" do not mean safe, and some natural products could even be deadly. After all, poison ivy is plant-based, natural, and can be grown organically and in a sustainable fashion, but this doesn't mean it will help you live your best life.

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