Selenium Benefits for Thyroid Disease, Cancer, and More

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Selenium benefitsSelenium (chemical symbol Se) is a trace mineral element found naturally in certain foods and available in supplement form. It is involved in multiple bodily processes, with research suggesting selenium benefits thyroid, cardiovascular, and cognitive health.

As an essential nutrient, selenium can only be obtained from the diet. Fortunately, you only need to consume a small amount to meet your daily needs.

Keep reading for more on the potential health benefits of selenium, exactly how much of it you need each day, and the best sources of the mineral.

5 Potential Selenium Benefits for Your Health

The human body uses selenium to make special antioxidant enzymes called selenoproteins. In addition to supporting DNA and thyroid hormone production, they may also protect the cells from free radical damage. This oxidative stress contributes to aging and an array of chronic illnesses.

Having low selenium levels, while relatively rare in the U.S. and Canada, can lead to serious health problems. Selenium deficiency has been linked to Keshan disease, a potentially deadly cardiomyopathy, or heart muscle disease, seen in remote areas of China.

Low selenium intake is also associated with a form of osteoarthritis called Kashin-Beck disease. This joint disorder is marked by arthritic pain; morning stiffness; reduced range of motion; and deformities/enlargements of the hands, wrists, knees, and ankles. It mainly occurs in regions of Siberia, North Korea, China, and Tibet.

Selenium deficiency is further linked to more common issues such as thyroid dysfunction and male infertility.

Researchers have examined the potential health benefits of selenium for various conditions. Let’s take a closer look at the findings.

Thyroid Disorders

The thyroid gland has the highest concentration of selenium of any organ in the body. It contains selenoproteins responsible for managing thyroid hormone metabolism.

Scientists began studying the relationship between selenium and thyroid function in the late 1980s. During that time, doctors in the Democratic Republic of Congo (formerly Zaire) were seeing an increase in cases of what was termed “myxedematous endemic cretinism.”

The condition was marked by selenium and iodine deficiency, severe hypothyroidism, thickening and swelling of the skin, intellectual disability, and developmental problems.

Investigations revealed that selenium deficiency lowers thyroid hormone production by decreasing the function of selenoproteins.

Decreased production of thyroid hormones may eventually lead to thyroid cell damage, fibrosis, and loss of thyroid function.

These issues are seen in autoimmune thyroid conditions such as Hashimoto’s disease (underactive thyroid) and Graves’ disease (overactive thyroid). Both occur when the body makes antibodies that attack the thyroid gland.

According to a review published in the journal Clinical Endocrinology, multiple studies indicate that selenium may reduce the number of antibodies while encouraging selenoprotein activity. This helps to lower inflammation, which could potentially relieve symptoms.

In Graves’ disease in particular, selenium supplementation seems to improve inflammation of the orbital (eye) tissues. This is one of the hallmark symptoms of the hyperthyroid disease.

However, in another systematic review and meta-analysis of nine trials, published in Endocrine in 2017, researchers found “no effect of selenium supplementation on thyroid stimulating hormone, health-related quality of life or thyroid ultrasound” in patients with autoimmune thyroid diseases.

Yet many nutritional supplements that help support thyroid hormone conversion of inactive T-4 to active T-3 do contain selenium. Therefore, more studies are needed to confirm the ability of selenium supplements to help treat or prevent thyroid disorders.


Preeclampsia is a high blood pressure condition that arises in pregnancy, usually after the 20th week. Besides sudden onset of high blood pressure, patients may also experience:

  • Severe headaches
  • Excess protein in urine
  • Changes in vision (blurriness, dark spots, light sensitivity)
  • Pain in upper right abdomen
  • Shortness of breath
  • Swelling in face, hands, and legs

Kidney and liver damage, seizures, blood clots, and stroke can occur in women in the absence of medical treatment. The baby may suffer fetal growth restriction, premature birth, or low birth weight.

Studies have shown that daily intake of selenium during pregnancy could lower the risk of preeclampsia.

One 1994 study found that taking a liquid selenium supplement prevented and decreased the incidence of pregnancy-induced hypertension and edema, both symptoms of preeclampsia.

In a 2006 study, pregnant women who supplemented with antioxidants daily, including 100 micrograms (mcg) selenium, had lower rates of preeclampsia. All participants in the study had screened positive for low antioxidant status in early pregnancy.

Pregnant women with or at risk for preeclampsia should discuss all treatment options with their doctor.

Heart Disease

The antioxidant properties of selenoproteins may work to prevent oxidation of fatty acids. This in turn may lower inflammation and block blood platelets from clumping together. Selenium is thought to have benefits against heart disease as a result, though study results have been mixed.

Some research has linked low selenium levels with a higher risk of cardiovascular disease. In a meta-analysis of 25 observational studies, a 50% increase in selenium blood content was associated with a 24% reduction in heart disease risk.

But similar studies have found either no association or that higher selenium levels may lead to an increased risk of heart disease.

Existing clinical trials also haven’t confirmed selenium’s ability to lower heart disease risk or death. It’s worth noting, however, that most trial participants have been adult males with no nutritional deficiencies.

Studies of the mineral’s effects on inflammatory markers have produced better outcomes. Markers of inflammation, such as C-reactive protein (CRP), have been associated with higher heart disease risk.

In a 2017 review of 16 randomized controlled trials (RCTs) with 43,998 participants, researchers found that selenium supplementation decreased serum CRP while increasing levels of the antioxidant glutathione peroxidase.

This suggests that selenium may lower inflammation and reduce oxidative stress related to heart disease.


Selenium’s potential to reduce inflammation and oxidative stress may also have positive effects on cancer prevention.

Researchers believe these anticancer effects specifically may include:

  • Restricting DNA damage
  • Boosting immune response
  • Activating tumor-suppressing genes
  • Triggering cancer cell death

One 2016 review and meta-analysis of 69 studies concluded that high blood levels of selenium decreased the risk of cancers including breast cancer, lung cancer, esophageal cancer, gastric cancer, and prostate cancer.

A later review of 83 RCTs involving 27,232 subjects found no evidence that increasing selenium intake could reduce the risk of any cancer type. However, the study authors recommended that future research examine factors such as participants’ genetic background and nutritional status, as well as differences between specific selenium compounds.

Cognitive Decline

Selenium deficiency may contribute to the oxidative stress associated with age-related degenerative brain disorders such as Alzheimer’s disease.

Alzheimer’s is characterized by progressive brain cell death. This often leads to memory loss, impaired thinking ability, and behavioral changes.

Selenium levels naturally decrease with age, and research has shown that Alzheimer’s patients have lower blood concentrations of selenium.

Supplementing antioxidants like selenium may improve memory decline.

In an analysis of 4,447 French adults aged 45 to 60 from the Supplementation in Vitamins and Mineral Antioxidants (SU.VI.MAX) study, researchers found that those supplementing antioxidants saw improvements in verbal memory.

Recommended Selenium Intakes

The body does not need large amounts of selenium to maintain good health. Most people in North America get enough of it through their diet since soil across the continent tends to be rich in the mineral.

The table below represents the recommended daily allowances (RDAs) for selenium according to age and sex.

Age Males (mcg/day) Females (mcg/day)
1-3 years 20 20
4-8 years 30 30
9-13 years 40 40
14-18 years 55 55
19-50 years 55 55
51 years and older 55 55

Pregnant and lactating women require 60 mcg and 70 mcg per day, respectively.

The tolerable upper intake level (UL), or the maximum daily intake that is unlikely to cause adverse health effects, for all adults aged 19-plus is 400 mcg.

Best Selenium Sources

Foods are the primary source of selenium for much of the population, and a number of foods are high in the micronutrient. However, it’s important to note that the amount found in foods will depend on the selenium levels in the local soil.

The soil provides plant foods with selenium. Animals in turn eat the plants and absorb their selenium, while humans eat these animals and the nutrient is passed on to them.

In the U.S., the lowest soil levels are generally found in the northwest and east coast states, though selenium deficiency is rare even in these regions.

Still, it is a good idea to get your selenium from a range of foods from different locales. Consider including the following selenium-rich foods in your diet:

  • Brazil nuts
  • Oysters
  • Yellowfin tuna
  • Halibut
  • Sardines
  • Ham
  • Shrimp
  • Beef steak (bottom round)
  • Turkey
  • Beef liver
  • Chicken
  • Cottage cheese
  • Brown rice
  • Egg (hard-boiled)
  • Whole-wheat bread

Some may choose to take a selenium supplement, either alone or as part of a multivitamin formulation. Vegetarians and vegans, those living with HIV/AIDS, and patients undergoing kidney dialysis are at higher risk for selenium deficiency, and might need to supplement as a result.

Supplements typically contain from 100 to 400 mcg selenium, and are available as tablets, capsules, liquid drops, or powders.

Selenium Risks

Selenium is essential to many biochemical functions in the body. But getting too much selenium (more than 400 mcg daily) can also cause problems, particularly selenium toxicity, or selenosis.

Initial symptoms may include:

  • Garlic, metallic taste in mouth
  • Hair loss
  • Brittle nails
  • Rash
  • Fatigue
  • Nausea
  • Diarrhea
  • Light-headedness

Left untreated, selenosis can turn severe, with complications like acute respiratory distress, heart attack, heart failure, kidney failure, and even death.

Selenium may also interact with certain medications, such as immunosuppressants, warfarin and other blood thinners, and sedatives (barbiturates). Always check with your healthcare provider before taking selenium or any other health supplement.

Finally, those with medical conditions including skin cancer, hypothyroidism (especially with iodine deficiency), and autoimmune disorders such as celiac disease, multiple sclerosis, or rheumatoid arthritis are strongly advised to work with their doctor to assess the benefits and risks of taking selenium supplements. Some medical sources report that supplementing the mineral may worsen these diseases.

Ask Your Doctor about Selenium Benefits for Your Health

Consult your primary care provider to help you determine if selenium supplementation is right for you, as well as how much and how often you should take the mineral remedy. While selenium supplements have shown great promise in a variety of therapeutic areas, additional research must be done before they can be widely recommended as treatments for the conditions covered in this article.

Also keep in mind that most people obtain enough selenium to keep their body healthy from their diet.

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