What Does Selenium Do in the Body? Function, Effects & Uses

Selenium (Se) is a trace mineral that is important for human health and has antioxidant and anti-inflammatory properties.

It plays an essential role in the body and is involved in protection from infection, thyroid hormone function, fertility and reproduction, DNA synthesis, antioxidant enzymes and energy metabolism.

Having too little selenium in your diet can impair immune system function, cause cognitive decline and increases the risk of mortality in general. Chronic low levels are associated with coronary artery disease and cardiomyopathy (diseases of the heart muscle).

Getting enough of this mineral from foods or supplements may overall health and reduce the risk of developing certain forms of cancer. High levels are associated with antiviral effects, improved reproduction in men and women and reduced risk for developing autoimmune thyroid disease.

However, there is some concern that supplementing selenium in those with already-adequate levels may increase the risk of type 2 diabetes mellitus. If you have excessive levels of selenium, you may be at risk of certain side effects.

Selenium

Essential Mineral

Anti-Oxidant

Immunity

Thyroid Function

How It Works:

• Cofactor for antioxidant enzymes
• Supports thyroid function & metabolism
• Promotes immune function & fertility

Dosage:

Up to 400 mcg per day

Safety:

Rated Likely Safe at Appropriate Dosages

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What Does Selenium Do In The Body?

Selenium exists in several different states in nature and in the human body. These include selenite, selenocysteine and selenomethionine.

Inside the body, selenium is incorporated into 25-30 specialized proteins called selenoproteins.

Selenoproteins demonstrate a wide range of biological effects; including helping with detoxifying heavy metals, protecting against excessive cellular H2O2 (hydrogen peroxide) and regulating both immunity and reproduction. [1]

Selenium is an important cofactor for the antioxidant enzyme family glutathione peroxidase which protects the body from oxidative damage. It also helps to recharge the antioxidant activity of other compounds such as Vitamin E.

It also facilitates proper functioning of the thyroid, helping to ensure adequate availability of active thyroid hormones.

Research is on-going to understand how selenium may impact numerous health conditions, including cancer, heart disease, thyroid disease and cognitive decline. [2]

Effects and Benefits

Having adequate selenium in the body is purported to have anti-aging benefits, support for healthy cholesterol levels and to support normal thyroid function.

As a dietary supplement, people take this essential mineral to promote detoxification pathways, healthy blood flow, normal prostaglandin levels, scavenging free radical molecules, and to support brain health.

According to Life Extension, “Studies show that selenium, a trace mineral, is an important common denominator among some of the world’s longest-living people.”

According to the Natural Medicines Database, a deficiency in selenium may lead to the following conditions:

• Kidney failure
• Selenium-Dependent Glutathione Peroxidase Deficiency
• Chronic Catarrhal Colitis (CCC)
• Irritated Bowel Syndrome (IBC)
• Chronic Recurrent Uveitis
• Coronary Heart Disease
• Cataracts
• Cancer
• Keshan Disease
• Iodine Deficiency Disorders
• Impaired Muscle Function
• Cirrhosis

While there may be benefits of selenium supplementation among individuals who have low levels of this mineral in their diet, it is not yet known what the positive effects are in people with adequate levels.

Selenium and Cancer

Some anticancer benefits of selenium have been shown in prospective studies. There seems to be some benefit associated with higher selenium levels concerning prostate, colon, lung and bladder cancers. However, the data is mixed.

Selenium may play a role in cancer prevention by its known effects on repairing DNA, regulating endocrine function, antioxidant cellular protection and boosting immunity. In in vitro studies, it has been shown to induce natural cell death (apoptosis) in some cancerous cells.

Placebo-controlled, randomized human trials addressing the potential anticancer benefits of selenium supplementation have yielded contradictory data. In one review of 9 such trials, the authors concluded that appropriate supplementation could help to reduce risk of gastrointestinal cancers.

In one double-blind, controlled and randomized trial, 1312 adults with skin carcinoma histories were monitored for several years. Subjects used a high-selenium yeast product that provided the equivalent dosage of 200 mcg/day. The results showed that this treatment reduced risk for developing prostate cancer between 52% and 65%. [3] However, in other similarly designed studies, no significant effect on cancer risk was found.

More human trials are needed to understand how selenium supplementation can affect risk factors for cancer. Research is ongoing.

Selenium and Cardiovascular Disease

Health experts have suggested that supplementing the diet with a selenium extract might reduce the risk of developing cardiovascular disease. It is known to have a positive effect on blood circulation and may generally support health health.

One of the ways it may work is by improving blood lipid profiles and impeding the development of arterial plaques. Selenoproteins help to slow down lipid peroxidation, decrease inflammation and inhibit blood platelets from aggregating.

Epidemiological studies on selenium and cardiovascular disease have yielded conflicting data. Some studies report an inverse relationship between the risk of high blood pressure (hypertension) and serum selenium levels.

One meta-analysis of 25 separate observational studies reported that low selenium levels increase the risk of developing coronary heart disease. Other studies suggest that higher selenium concentrations increase the risks for heart disease, cardiovascular disease and cardiac death. [4]

Although some human research suggests benefits of supplementation for preventing cardiovascular disease, overall existing evidence does not support this use. More randomized, controlled trials are needed to determine if and how selenium contributes to cardiovascular health.

Selenium and Cognitive Decline

It is known that blood levels of selenium decrease with aging in most people. More than one study suggests that deficient or even marginally-deficient selenium concentrations may be associated with cognitive decline.

The most likely reason is that selenium has antioxidant properties which may protect brain cells from cumulative oxidative damage.

Existing evidence is not sufficiently clear to make any conclusive determinations. In two large human trials, subjects with low baseline levels of plasma selenium had increased risks for cognitive decline with age.

In these studies, it was not clear if the subjects were simply low in selenium or clinically deficient.

An analysis of NHANES data on more than 4800 US residents found no association between low selenium and memory impairment. While some combination supplements containing selenium seem to improve cognitive functioning, it is unclear if selenium can act alone to do so.

More human research is needed to understand if and how selenium might affect cognitive decline, age-related memory function and brain health.

Selenium and Thyroid Disease

The thyroid gland holds more selenium than any other organ in the human body. Along with iodine, selenium is very important for proper thyroid functioning.

Three of the most important Selenoproteins in the body include the iodothyronine deiodinase enzyemes, which are responsible for catalysing the conversion of the active form of thyroid hormone from its inactive precursors.

Analysis of evidence from epidemiological studies of more than 1900 subjects supports a relationship between adequate selenium and thyroid health. There is an inverse relationship between selenium levels in serum and risk of thyroid tissue damage, risk of goiter (enlarged thyroid) and thyroid volume.

Without selenium, the prohormone thyroxine or T(4) cannot get converted into the active hormone triiodothyronine T(3). This results in impaired energy metabolism and cellular growth throughout the body.

However, if you are not deficient in this compound, it is not likely that increasing your intake of selenium will improve availability of active thyroid hormone. In two studies, supplementation was not shown to affect thyroid hormone function in elderly individuals or healthy men.

The effects of supplementing with this mineral for thyroid function are not clear yet. Some studies have shown that significant increases in selenium availability have no effects on thyroid function at all.

The Natural Medicine Comprehensive Database states that selenium is Possibly Effective for autoimmune thyroiditis. More human trials are required to determine any efficacy of selenium for preventing or treating thyroid disease.

Selenium Side Effects and Interactions

Selenium has been rated Likely Safe by NMCD when used orally at appropriate dosages. It is safe for use in short periods of time up to a dosage of 400 mcg/day.

The US RDA (Recommended Dietary Allowance) for selenium is 55 micrograms per day for males and females over the age of fourteen.

Too much selenium over time may cause adverse side effects. The most common early indicators of excess selenium intake are metallic taste in the mouth and breath that smells like garlic.

Other side effects of selenosis include skin lesions, diarrhea, nausea, fatigue, skin rashes and mottled teeth. Irritability and nervous system abnormalities are also possible.

Selenium supplementation may also cause interactions with certain medications, herbal supplements, diseases and lab tests. It is best to seek medical advice about the best dosage level of selenium for you.

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