Selenium and Your Thyroid

brazil nuts

Selenium is a crucial nutrient for your health, and is essential to thyroid hormone metabolism, among many other key functions.

Selenium is a mineral that is found in some foods we eat, added to foods to fortify them, and can also be taken as a dietary supplement. The body does not manufacture selenium, so the only way we get selenium is through food and supplements.

Selenium levels can be measured by blood tests. Hair analysis can evaluate longer-term selenium levels. According to the National Institutes of Health, a healthy level of selenium is 8 micrograms (mcg)/dL or higher. In the United States, selenium deficiency is fairly rare, and most people are getting the required amount of selenium.

There are some risk factors for selenium deficiency, including:

  • Intestinal, digestive, or absorption issues
  • Having had gastric bypass surgery
  • Living in an area with selenium-deficient soil
  • Cholesterol-lowering statin drugs

The Brazil nut is known to have very high levels of selenium. Other foods that are sources of selenium include certain seafoods—such as shrimp, sardines, salmon, halibut, and tuna—and meats, poultry, mushrooms, bread, cereals, grains, eggs, and dairy products.

Selenium is available as a supplement, either alone, or in combination formulas in multivitamins. There are two forms of selenium: selenomethionine, or sodium selenite. Research has shown that there is better absorption for the selenomethionine form of selenium. Experts recommend that adults get no more than 400 mcg of selenium daily from all sources. High levels can result in selenium toxicity, with symptoms such as hair and nail loss, nausea, rashes, and nervous system abnormalities. In particular, be careful about Brazil nuts, because they contain so much selenium—in some cases as much as 100 mcg per nut—that you can trigger selenium toxicity.

Selenium’s Impact on the Thyroid

The thyroid is the organ that concentrates selenium more than any other. Selenium plays a key role in your thyroid gland’s ability to produce thyroid hormone.

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. Several studies have found an inverse relationship with selenium levels and your risk of goiter (an enlarged thyroid), and damage to your thyroid gland in people with iodine deficiency.

A number of research studies have shown key relationships between selenium supplementations—even when there is not a deficiency—and thyroid function. For example:

  • Several studies have shown that supplementing with selenium reduces thyroid peroxidase antibodies (TPO) as well as the severity of hypothyroidism symptoms.
  • One study found that 200 mcg of selenium given to pregnant women with thyroid peroxidase (TPO) antibodies could reduce the risk of postpartum thyroiditis.
  • One study found that treating patients with mild thyroid eye disease with 200 mcg/day of selenium for six months improved patient quality of life, improved outcomes for their eye health, and dramatically slowed progression of symptoms.

Of particular interest is a 2016 study reported on in the journal Thyroid that 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 3, 6, and 12 months of selenium supplementation in two groups of Hashimoto’s patients; one receiving levothyroxine thyroid hormone replacement treatment, and the other being newly-diagnosed patients not being treated with thyroid hormone replacement.

The findings were very interesting. For those Hashimoto’s patients being treated with levothyroxine for thyroid hormone replacement, selenium supplementation resulted in significantly lower TPOAb levels after three months, and those levels continued to decrease at 6 months and 12 months. Additionally, TgAb 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 6 or 12 months, while TgAb decreased at 3 months, but not at 6 or 12 months.

Should You Increase Your Selenium Intake?

Before you consider adding handfuls of Brazil nuts to your diet, or taking selenium supplementation, you may want to have your selenium levels evaluated by your physician. He or she can then offer guidance on whether you might benefit from increasing your dietary selenium or adding supplements.  Keep in mind that even 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 does not exceed 400 mcg daily.

View Article Sources
  • Drutel, A, Archambeaud F, and Caron P. "Selenium and the Thyroid Gland: More Good News for Clinicians." Clin Endocrinol Clinical Endocrinology 78.2 (2013): 155-64. PubMed. 30 Mar. 2016.
  • Hu, S et al. “Multiple nutritional factors and the risk of Hashimoto’s Thyroiditis.” Thyroid. March 2017. doi:10.1089/thy.2016.0635.
  • Kafai MR, Ganji V. Sex, age, geographical location, smoking, and alcohol consumption influence serum selenium concentrations in the USA: third National Health and Nutrition Examination Survey, 1988-1994. J Trace Elem Med Biol 2003;17:13-8.
  • Niskar AS, Paschal DC, Kieszak SM, Flegal KM, Bowman B, Gunter EW, et al. Serum selenium levels in the US population: Third National Health and Nutrition Examination Survey, 1988-1994. Biol Trace Elem Res 2003;91:1-10. 
  • Wichman J et al. “Selenium Supplementation Significantly Reduces Thyroid Autoantibody Levels in Patients with Chronic Autoimmune Thyroiditis: A Systematic Review and Meta-Analysis.” Thyroid. Volume 26, Number 12, 2016 DOI: 10.1089/thy.2016.0256