The Health Benefits of Selenium

The Health Benefits of Selenium


Introduction & Biological Role

Selenium is an essential mineral found in small amounts in the body.

Known functions in the body of selenium include functioning as an antioxidant, helping to repair damaged cells and DNA. Free radicals are known to contribute to the aging process and may worsen other health conditions including heart disease and cancer. Selenium plays a role in maintaining normal thyroid function. It’s also critical in reproduction and DNA synthesis as well as immune function.

Selenium exists in two forms, both of which are good dietary sources, inorganic (selenate and selenite) and organic (selenomethionine and selenocysteine)

Health Benefits/ Uses

Heart Disease

The evidence is mixed. Folks with low levels of selenium are known to be more likely to develop heart failure and atherosclerosis or hardened arteries, increasing risk of heart attack and stroke. However, supplementation with selenium alone does not seem to help reduce the risk of these disease processes.


One study showed that when selenium is combined with vitamin E and beta-carotene, it may help lower the bad form of cholesterol known as LDL or low density lipoprotein. It’s also known to reduce the effectiveness of statins which are the primary medicine used to reduce cholesterol.

Immune Function

Selenium is thought to help a properly functioning immune system, primarily by boosting white blood cell activity, improving the body’s ability to fight infections. One study showed that selenium and zinc supplements improved the body’s response to the flu vaccine. It may also help prevent infections such as skin infections associated with lymphedema and mycoplasma pneumonia.


Low levels of selenium are associated with an increased risk of cancer. This is known by large scale studies where people live in areas with soil rich in selenium have lower rates of certain cancers. People who develop cancer are often also found to have low levels of selenium in their body.

Evidence is mixed whether supplementing selenium can lower your risk of developing cancer, regardless of whether you have normal or low levels. It does seem to have a marginal effect in reducing your overall death from cancer. It does not seem to lower the risk from lung or esophageal cancer. Evidence is mixed regarding colorectal cancer (some studies show benefit, others do not). It may help with prostate cancer, especially when taken in the form of selenium rich brewer’s yeast.

It’s important to point out that researchers thought selenium may protect against skin cancer. However, a large scale trial found that supplementation increased the risk of non-melanoma types of skin cancer.

You are advised not to supplement without talking to your doctor.


Folks with asthma tend to have lower levels of selenium. In one small study, folks who supplemented selenium had fewer asthma symptoms over 14 weeks than those who took the placebo. Another study found no difference. More research is needed before we can draw any conclusions.


There is mixed evidence regarding selenium and HIV and AIDS. One study showed that supplementation slowed progression of the disease, and another study found no difference. Talk to your infectious disease specialist before supplementing for this purpose.

Rheumatoid Arthritis (RA)

Although folks with rheumatoid arthritis are found to have lower levels of selenium, supplementation does not seem to make a huge difference.

Cognitive Decline

Serum levels of selenium appear to decrease as we age. Some studies have suggested lower selenium levels associated with poorer mental function, however another study found no link between selenium and memory. More research is needed.

Thyroid disease

The thyroid gland is a major storage area for selenium. It remains unclear whether selenium supplementation can help improve thyroid dysfunction, a disease primarily associated with iodine deficiency.


If you eat a balanced diet, you are unlikely to have a selenium deficiency.

Those at risk are individuals with kidney disease who are on dialysis, folks with HIV or those living in areas with low levels of selenium in the soil.

Deficiency, although rare, can lead to keshan disease (type of heart disease specific to selenium deficiency), infertility in men, kashin-beck disease (a type of arthritis).


Although toxicity is rare, symptoms are vague and can include fingernail loss, skin rash, fatigue, irritability, weight loss, nausea and diarrhea, discolored teeth, metallic taste in mouth and central nervous system problems.


Selenium content of food is largely dependent on the soil it was grown in.

The best dietary sources generally include seafood (mackerel, tuna, halibut, flounder, herring, and smelts), meat, poultry, eggs, dairy, and grain based products (brewer's yeast and wheat germ), sunflower seeds and brazil nuts.

Top 10 sources according to NIH

  1. Brazil nuts (544 mcg, 777%)- comment on excessive content
  2. Yellowfin Tuna (92 mcg, 131%)
  3. Halibut (47 mcg, 67%)
  4. Sardines (45 mcg, 64%)
  5. Ham (42 mcg, 60%)
  6. Shrimp (40 mcg, 57%)
  7. Macaroni (37 mcg, 53%)
  8. Beef steak (33 mcg, 47%)
  9. Turkey (31 mcg, 44%)
  10. Chicken (22 mcg, 31%)

Recommended Daily Allowance (RDA) based on the USDA:

  • 19 and older: 55 mcg
  • Pregnant women: 60 mcg
  • Breastfeeding women: 70 mcg

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