Selenium is an essential mineral, classified as a micronutrient or microelement, that acts as a building block for important enzymes in the body. Research shows a large body of evidence of its necessity for optimal health, but much is still unknown about this complex substance, which though essential, can actually harmful in the wrong forms and amounts.
Importance of Selenium
Low dietary and blood levels of selenium are associated with a number of health issues. Animal studies show that low folate and selenium during pregnancy can affect the metabolism of offspring (Source) and may be linked to higher miscarriage risk. (Source) Selenium deficiency is also tied to endometriosis and poor uterine health. (Source)(Source) Individuals with enlarged thyroid glands were found to have low levels of selenium (Source) and may be a factor for thyroid cancer risk. (Source) Several studies have also found that celiac patients are low in selenium, although it’s not known if it’s causative or due to absorption issues. (Source)(Source) Research also shows low selenium to be prevalent in those with inflammatory bowel diseases such as Chron’s disease and ulcerative colitis (Source) as well as Alzheimer’s Disease. (Source)
Selenium as an Antioxidant
Many studies have shown the antioxidant powers of this unique element, from anti-oxidant effects on LDL cholesterol (Source) to helping improve blood lipid and glucose profiles.
Our findings suggest that selenium restores a normal metabolic profile and ameliorates vascular responses and endothelial dysfunction in diabetes by regulating antioxidant enzyme and nitric oxide release. (Source)
Selenium plays a critical role in the prevention of colon cancer, with special forms of selenium even being studied as a potential cancer treatment. (Source)(Source) Selenium’s exact function in gut health is still being studied, but it is thought to create certain proteins that alter the function of cells to an anti-inflammatory state. (Source)
Selenium has been found to be helpful in the treatment of kidney disease and supporting kidney transplants (Source) and a selenium compound, l-selenomethionine, was found to help support thyroid function in Hashimoto’s thyroiditis. (Source)
Too Much Selenium
Selenium offers many health benefits, but it can be dangerous if taken in high doses. While the benefits of selenium are supported by much research, evidence also shows the negative implications of taking too much of the nutrient. Essentially, problems typically arise when selenium is too high from taking supplements.
High levels of selenium have been found to increase LDL cholesterol levels, (Source)(Source)(Source) and while some studies have shown that selenium can aid in supporting glucose control, higher selenium levels have been associated with increased diabetes risk. (Source)
A review article  that comprehensively investigated the association between selenium and type 2 diabetes concluded that this complicated relationship may be explained by the possible harm that occurs both below and above the physiological range for optimal activity of some or all selenoproteins. The present study and a previous one  were both conducted on a population with mean dietary selenium intake close to the RNI, but the association in a population with very low dietary selenium intake may be different. Previous review articles suggested that the association between selenium and diabetes might be U-shaped: selenoproteins both below and above the physiological range might become a risk factor for diabetes [1,3,34].(Source)
In other words, selenium deficiency is harmful, yet an excess amount is harmful as well.
While low selenium has been tied to risk for thyroid conditions, and selenium is an essential trace mineral for enzymatic function within the thyroid (source) it was found that selenium supplementation was not helpful for improving thyroid conditions. (Source) Perhaps, again due to the forms in the supplementation or the higher doses. This recent review found that there was not significant evidence to prove that selenium supplementation helped prevent or cure cancer and further highlighted the idea that while low selenium levels have been found in people with certain illnesses, we’re still not sure if it’s a symptom or a cause of the illnesses.
A Fine Balance
If you’re selenium deficient, it can make you sick, but if you have too much selenium it can also cause problems. Testing for selenium is not typically included in standard blood panels and much is still being debated about what should be tested for. Some will test for overall selenium levels, while others say that testing for selenoproteins glutathione peroxidase and selenoprotein P are more accurate. Once the body incorporates selenium, there are so many different compounds it makes with it and we don’t know which compounds are indicators of optimal health. (Source) (Source)
It seems that much of the function of selenium has to do with how it reacts with the bacteria in our digestive tracts. (Source) (Source) And the inorganic forms of selenium found in supplements like sodium selenite, sodium selenate, and selenium dioxide may be harmful, and could be why many studies on selenium supplementation have shown negative outcomes. (Source) The forms of selenium found in foods is identical to the form our body needs, amino acids called selenomethionine and selenocysteine. (Source)
- Get your selenium from foods, not supplements.
- Support your gut with healthy probiotics and a high-fiber diet so it can best utilize selenium.
- Brazil nuts are the #1 food for selenium, with just 1 nut providing 100% of your RDA.
- Don’t look to selenium to be a cure-all or preventative supplement on it’s own; it should be trace mineral that’s present in a healthy controlled-carb, high-fiber, high-vegetable diet that supports your overall health.