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Selenium is an essential trace mineral that supports many bodily processes. It can help improve cognition, immune system function, and fertility.

Selenium is a nutrient that plays a key role in maintaining thyroid hormone metabolism and DNA synthesis and protecting the body from oxidative damage and infection. This is according to the Office of Dietary Supplements (ODS).

The body typically stores some selenium in human tissue, mostly in skeletal muscles, after getting it from foods containing trace amounts. These foods include Brazil nuts, seafood, and meats.

The amount of selenium in food depends on the concentration of the soil and water where it grew. People can also add the mineral to foods or consume it as a supplement.

This article looks at the potential health benefits of selenium when a person consumes it from food or supplements, the recommended daily intake of selenium, and some possible health risks associated with selenium.

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Selenium may play a role in several aspects of human health, but scientists are still doing more clinical research to determine the nutrient’s impact.

The following sections look at some possible health benefits in more detail.

Cardiovascular disease

According to the ODS, selenoproteins may affect heart health by preventing the oxidative modification of lipids, or body fats. This may reduce inflammation and the buildup of platelets.

However, there is no consistent clinical evidence to suggest that the mineral lowers the risk of cardiovascular disease, especially in healthy people who already get selenium from food. Some studies do indicate that people with less selenium in the blood are at higher risk of heart disease, but other studies refute this.

Cognitive decline

Selenium’s antioxidant activity may help reduce the risk of both age-related cognitive decline and impairments that result from conditions such as Alzheimer’s disease.

However, doctors do not yet recommend selenium for this purpose. Like with heart health, the degree of selenium’s impact on cognitive decline is still under investigation, according to studies in the Journal of Alzheimer’s Disease and the Journal of Trace Elements in Medicine and Biology Evidence.

Thyroid disorders

Selenium also has an important role in maintaining healthy thyroid function.

Studies in the International Journal of Endocrinology and Nature Reviews Endocrinology suggest that having an optimal level of selenium in the body may help prevent thyroid disorders. This could especially be true for females.

However, more research is underway to help inform how selenium supplements might support thyroid health.

Cancer

Selenium’s role in DNA repair means that it may play a role in cancer prevention. However, this may depend on the type of selenium and the type of cancer a person has, according to a 2016 study.

Other studies cited in a 2018 review indicate that selenium supplements may have little effect on cancer risk.

Other benefits

Some studies indicate that selenium may also help prevent HIV from progressing to AIDS and reduce the risk of miscarriage.

Scientists have also suggested that selenium levels during pregnancy may be a factor in the development of childhood asthma.

However, although selenium has links with many aspects of human health, there is not enough evidence to indicate that taking selenium supplements can prevent any of these conditions.

Selenium is most often found in whole grains and animal products such as fish and eggs. The amount of selenium in grains and grain-based foods depends on the soil content where they grew.

The following foods are good sources of selenium:

  • Brazil nuts: One ounce provides 544 micrograms (mcg), or 989% of the recommended Daily Value (DV).
  • Tuna: Three ounces of yellowfin tuna, cooked dry, contains 92 mcg, or 167% of the DV.
  • Baked halibut: Three ounces, cooked dry, contains 47 mcg, or 85% of the DV.
  • Cooked brown rice: One cup contains 19 mcg.
  • Egg: One large egg contains 15 mcg.
  • White bread: One slice provides 10 mcg.

The recommended DV for selenium is 55 mcg per day for most adults. During pregnancy, a person should consume 60 mcg, and while lactating, they should consume 70 mcg per day.

Selenium deficiency is rare worldwide, and it often takes years to develop. It usually only occurs in regions with severely low selenium content in the soil, such as several regions in China. However, according to the ODS, supplementation programs have mostly eradicated these deficiencies in the Chinese population.

The upper limit for the optimal level of selenium in the body is 400 mcg for adults. It is rare for anyone to overdose on selenium, especially from selenium in food.

However, an overdose of highly concentrated supplements can have negative effects. These may include:

  • a garlic-like smell on the breath and a metallic taste in the mouth
  • brittle nails
  • mottled or decaying teeth
  • gastrointestinal problems, such as nausea
  • neurological anomalies
  • fatigue and irritability
  • skin lesions and rashes
  • hair loss

In extreme cases, selenium overdose could lead to kidney failure, heart failure, and death.

Selenium supplements can also interact with some medications, including cisplatin, which is a chemotherapy drug. The use of this drug can reduce selenium levels in the body.

People can get selenium through multivitamins and other dietary supplements. These may contain the mineral in different forms, including selenomethionine and sodium selenate.

The Dietary Guidelines for Americans, 2020–2025 encourage people to get their nutrients from food sources rather than supplements. Eating a varied and healthful diet is more important than concentrating on individual nutrients as the key to good health.

When taking any supplement, it is important to purchase it from a reputable source. In the United States, the Food and Drug Administration (FDA) does not monitor supplements for quality, purity, packaging, or strength.

Selenium supplements are available for purchase online.

Selenium is a mineral that may provide different health benefits. For example, it may help with cardiovascular health, cognitive function, and thyroid health.

The optimal daily amount of selenium for most adults is 55 mcg, and selenium deficiency is rare.

People can get selenium from foods that contain it, and they can also add it to food or consume it as a supplement. However, more research is needed to determine whether or not taking selenium supplements can actually reduce disease risk or help prevent health problems.