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 or hyperthyroidism. On the other hand, some products may interfere with the absorption of thyroid hormones, affect testing, or pose other dangers. Knowing more about some common supplements and their effect on thyroid disease (for better or for worse) can help you make the right choices for your overall health.

Common Thyroid Disease Supplements

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.

Vitamin D

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

In addition, low vitamin D levels are associated with an increased risk of developing autoimmune thyroid diseases such as Hashimoto's thyroiditis and Grave's disease in the first place.

It's thought that the majority of people in the United States have low levels of vitamin D. Fortunately, a simple blood test can help you know whether you are deficient or not. Make sure to talk to your doctor about taking vitamin D, as an excess can lead to side effects such as painful kidney stones.

Vitamin B12

Vitamin B12 deficiency is relatively common (especially in people over age 50). Furthermore, the drug metformin, often used to aid in weight loss and to decrease insulin resistance in people with hypothyroidism, may reduce B12 levels.

The symptoms of vitamin B12 deficiency can mimic many of the symptoms of hypothyroidism, so a deficiency can be easy to miss.

Since both under-treated hypothyroidism and vitamin B12 deficiency are linked with an increased risk of stroke, even in young people, it's important to make sure you receive adequate amounts of the vitamin. Vitamin B12 is obtained from meat and animal products, but even with adequate intake, poor absorption due to age or digestive conditions may necessitate using a supplement.

Omega-3 Fatty Acid Supplements

Omega-3 fatty acids, especially icosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are thought to be particularly beneficial for people with autoimmune thyroid diseases for both their anti-inflammatory and immune modulating properties. They can be obtained eating fatty fish (such as salmon, herring, tuna, and mackerel) at least two to three times per week or through fish oil supplements.

It's important to purchase good quality fish oil to avoid excess mercury levels. 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.

CLA can cause gas and digestive upset in some people. If you are trying to lose weight with hypothyroidism, ask your doctor for her recommendations.

Iodine

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

Selenium

Selenium is important in thyroid hormone metabolism and a 2018 study found that selenium supplementation may reduce anti-thyroperoxidase antibody levels in people with autoimmune hypothyroidism. In those with Grave's disease (hyperthyroidism), improvements were noted in thyroid antibodies as well as quality of life.

Selenium has a narrow "therapeutic window," meaning that even small excesses can be toxic.

Zinc

Zinc is needed for the synthesis of thyroid hormones in the body, and a 2018 study found these supplements to have some benefit for women with hypothyroidism who are overweight and obese. A deficiency of zinc can also lead to hypothyroidism and other autoimmune diseases.

Thiamine (Vitamin B1)

There is some evidence that thiamine supplements may reduce fatigue in people with Hashimoto's thyroiditis. Autoimmune thyroid disease such as Hashimoto's disease and Graves' disease/hyperthyroidism can lead to reduced absorption of thiamine even with adequate intake, so people with thyroid disease may wish to talk to their doctor about supplementation.

Supplements That Affect Medications & Tests

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

supplements that interfere with thyroid medication
Illustration by Emily Roberts, Verywell

Calcium and Iron

Calcium and iron supplements should be taken at least three to four hours after levothyroxine to avoid reduced absorption of the drug.

Beyond that, though, 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

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" or "adrenal support," or that 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 other thyroid hormone treatment options, such as Armour Thyroid.) 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 for weight loss and energy, the dangers of ephedra outweigh any benefits and could be particularly concerning for people with hyperthyroidism (by further increasing heart rate, blood pressure, and other issues).

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? How long do you need to wait after taking levothyroxine before taking the supplement?
  • 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 to being relatively unregulated in the United States, some dietary supplements could be dangerous for some people and can interact with a number of drugs, including thyroid hormones.

Talk to your doctor before taking any of these products. If your doctor is unfamiliar with supplements or herbal therapies, you can seek the advice of a naturopathic doctor. Just be sure the physician treating your thyroid disease is kept in the loop about what you discuss.

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