What to Know About Selenium and Your Thyroid

The nutrient is essential for thyroid function

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Selenium is a crucial nutrient for everyone's health. It's essential to thyroid hormone metabolism, reproduction, DNA synthesis, and it protects you from infection and damage resulting from oxidative stress. Selenium is a mineral that's naturally found in some of the foods we eat. It's also added to foods to fortify them and can be taken as a dietary supplement. Your body doesn't make selenium, so the only way you can get it is through food and/or supplements.

Selenium’s Impact on the Thyroid

In adults, the thyroid is the organ that has the highest concentration of selenium in the body, and this mineral plays a key role in your thyroid gland’s ability to produce thyroid hormone. Having an optimal amount of selenium in your diet is vital not just for preventing thyroid disease, but for your overall health.

A selenium deficiency is associated with a variety of thyroid issues, including:

Iodine—the building block and key ingredient of thyroid hormone—actually requires selenium in order to be synthesized properly into thyroid hormone. Hashimoto's thyroiditis, the most common autoimmune disease, is associated with a high intake of iodine, selenium and iron deficiencies, and possibly a vitamin D deficiency as well, though the low vitamin D levels may be due to the disease itself.

What the Research Shows

A number of research studies have shown key relationships between selenium supplementation and thyroid and immune function. For example:

  • Both excessively high and low levels of selenium have been associated in several studies with an increased risk of disease.
  • Several studies have shown that supplementing with selenium reduces thyroid peroxidase antibodies (TPO), as well as the severity of hypothyroidism symptoms.
  • Some studies have found that treating patients who have mild to moderate thyroid eye disease (Graves' orbitopathy) with selenium supplements improved quality of life, as well as outcomes for their eye health, and dramatically slowed progression of symptoms. The European Thyroid Association now recommends a six-month trial of selenium supplementation for patients with Graves' orbitopathy.
  • Even for people who don't have a selenium deficiency, taking selenium supplements has been shown to have a considerable impact on the immune system, increasing the production of activated T-cells and natural killer cell activity, both of which assist in the immune response to disease, tumors, and infection.
  • A 2016 study analyzed the impact of selenium supplementation on the thyroid antibody levels of people with Hashimoto’s thyroiditis. The study evaluated both thyroid peroxidase (TPOAb) and thyroglobulin (TgAb) antibody levels at three, six, and 12 months of selenium supplementation in two groups of Hashimoto’s patients; one receiving levothyroxine thyroid hormone replacement treatment, and the other, as newly-diagnosed patients, not being treated with thyroid hormone replacement. For those being treated with levothyroxine, selenium supplementation resulted in significantly lower TPOAb levels after three months, which continued to decrease at six months and 12 months. TgAb levels did not decrease until the 12-month point. In the untreated Hashimoto’s group, selenium supplementation resulted in a decrease in TPOAb levels after three months, but not after six or 12 months, while TgAb decreased at three months, but not at six or 12 months.

    Selenium Deficiency

    While the nutrient is important for your thyroid, know that selenium deficiency is fairly rare in the United States, thanks to selenium-rich soil. Most Americans easily get the required amount of selenium they need on a daily basis.

    While the odds of a deficiency are pretty low for most, there are some people for whom the risk is greater. Some of the risk factors for developing a selenium deficiency include:

    • Intestinal, digestive, or absorption issues like Crohn's disease
    • Having had gastric bypass surgery
    • Living in an area with selenium-deficient soil
    • Undergoing kidney dialysis
    • Having human immunodeficiency virus (HIV)

    Symptoms

    There are many symptoms that can occur when you aren't getting enough selenium. Some of the most common ones include:

    • Infertility
    • Hair loss
    • Fatigue
    • Weight gain
    • Compromised immune system, resulting in getting sick more often
    • Difficulty thinking and/or concentrating

    Of course, it's worth noting that some of these overlap with symptoms of thyroid disease.

    Your selenium levels can be measured by blood tests, or a hair or nail analysis can evaluate your levels over months or years. According to the National Institutes of Health, a healthy blood level of selenium is 8 micrograms (mcg)/dL or higher.

    Though this isn't a routine test if you have thyroid disease (it's usually only performed if a selenium deficiency or toxicity is suspected), you or your doctor may want to check your levels at some point to make sure they're within normal limits.

    Daily Recommendations

    It's helpful to know what your goal should be, particularly if you have any of the symptoms mentioned above.

    The Food and Nutrition Board (FNB) at the Institute of Medicine of the National Academies recommends that healthy people age 14 years and older get 55 mcg of selenium daily from all sources. The recommendation goes up to 60 mcg per day if you're pregnant and 70 mcg per day if you're breastfeeding. You can safely take in up to 400 mcg per day between food and supplements.

    Forms and Sources

    There are two forms of selenium: organic (selenomethionine and selenocysteine) and inorganic (selenate and selenite). Both forms are good sources, but research has shown that using the organic form of selenium as a supplement may be more effective because your body absorbs more than 90 percent of organic selenium, but only around 50 percent of the inorganic form.

    Foods that are good sources of selenium include:

    • Brazil nuts
    • Seafood, such as shrimp, sardines, salmon, halibut, and tuna
    • Meats like beef steak, beef liver, ground beef, and ham
    • Poultry
    • Eggs
    • Breads
    • Cereals
    • Grains

    Selenium can be found in supplements either alone or in combination formulas in multivitamins. Due to its overall effects in the body, research is being conducted on whether or not selenium supplementation may help prevent cancer, thyroid disease, heart disease, and the cognitive decline that occurs as we age.

    Selenium Requirements and Dietary Sources

    Selenium Toxicity

    While low levels of selenium are a concern, high levels can result in selenium toxicity over time. Symptoms include:

    • Garlic smell to the breath
    • Metallic taste in the mouth
    • Hair and nail loss or brittleness
    • Nausea
    • Skin rashes
    • Diarrhea
    • Skin lesions
    • Fatigue
    • Irritability
    • Nervous system abnormalities

    In particular, be careful with Brazil nuts; because they contain so much selenium—as much as 90 mcg per nut—you can actually trigger selenium toxicity by eating them too often.

    Benefits and Risks

    Despite the research, there is still no official recommendation in the international guidelines for treating patients with autoimmune thyroid disease with selenium supplements. For those with thyroid disease and low selenium levels, supplementation can be beneficial, but for those whose selenium levels are normal to high, supplementation could potentially result in toxicity.

    A Word From Verywell

    Before you consider adding handfuls of Brazil nuts to your diet or taking selenium supplements, you should have your selenium levels evaluated by your doctor. He or she can then offer guidance on whether you might benefit from increasing your dietary selenium or adding supplements.

    Keep in mind that if you choose to supplement with selenium, you should calculate your dietary intake, and be sure to count any selenium in multivitamins and supplements so that your daily intake doesn't exceed the 400 mcg daily recommended upper intake level.

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