Selenium: A Mineral Essential for Detox/Redox

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Guarding against environmental toxins

Selenium is a mineral with remarkable antioxidant benefits. Although it is needed only in small amounts, selenium is vital for thyroid, reproductive and immune function, and for protecting the brain, heart, and kidneys against environmental toxins.[1]

Selenium is like a battery that operates within 25 different selenium-containing proteins (selenoproteins) in mammalian cells.[2] Some selenoproteins are enzymes that catalyze redox (reduction/oxidation) reactions, while others help transport selenium to target tissues. The most important redox managers in human cells are enzymes known as glutathione peroxidase (GPx) and thioredoxin reductase (TrxR).[2] There are eight forms of GPx in human cells, and each has slightly different actions. GPx1, for example, uses glutathione and converts hydrogen peroxide to water, thereby keeping the peroxide from damaging cells. These enzymes cannot function without selenium.

Although it is needed only in small amounts, selenium is vital for thyroid, reproductive and immune function, and for protecting the brain, heart, and kidneys against environmental toxins.

Science is beginning to reveal the many ways in which selenium keeps the redox machinery rocking along. These include:

Protection against heavy metals

Selenium helps protect against the toxic effects of heavy metal exposure. No, we’re not talking about loud music here (although some of us would like to protect against that too!). The term heavy metal refers to any metallic chemical element that has a high density relative to water and is toxic or poisonous at low concentrations.[3],[4] Examples of heavy metals include mercury, cadmium, arsenic, and lead, which are among the 10 substances most dangerous to public health.[5]

Heavy metal exposure can occur through many different routes, including via the water we drink, foods we eat, air we breathe, and substances that contact our skin. A significant amount of the damage associated with heavy metal-induced toxicity is due to the production of reactive oxygen species, resulting in tissue damage and adverse health effects. The related health issues may include cardiovascular disorders, nerve and brain damage, poor bone growth, kidney injury, and an increased risk of cancer and diabetes.[6]

Methylmercury (MeHg), prevalent in the seafood we eat, and elemental mercury (Hg0), found in dental amalgams, has been studied in great detail. It is toxic to the nerves, kidneys, immune system, and gastrointestinal tract. [4],[7] The toxic effects of mercury are in part attributed to its sequestration of selenium and the irreversible inhibition of selenoproteins (such as TrxR),[8] especially those required to prevent and/or reverse oxidative damage in the brain, one of the fatty tissues in which mercury readily accumulates.[9],[10]

Selenium mitigates the toxic effects of environmental mercury, lead, arsenic, and cadmium by forming an insoluble complex (chelate) with these metals and reversing the oxidative damage.

Selenium mitigates the toxic effects of environmental mercury, lead, arsenic, and cadmium by forming an insoluble complex (chelate) with these metals and reversing the oxidative damage. [10],[11],[12],[13],[14] Maintaining a steady supply of selenium is important, because low plasma selenium levels exacerbate the health risks associated with mercury and other heavy metals.[15] In mercury-exposed residents of Wanshan, China, for instance, supplemental selenium decreased oxidative damage, reduced the mercury burden in the body, and increased mercury excretion.[16]

Selenium also safeguards against organic pollutants and toxicants such as herbicides,[17] bisphenol A (BPA),[18] and mycotoxins (mold toxins) such as ochratoxin A.[19],[20] Last but not least, animal studies have shown that selenium supplementation could prevent the oxidative stress and cardiovascular inflammation induced by air pollution particulates (PM2.5).[21]

Selenium’s synergy with other antioxidants and nutrients

The metabolism and subsequent excretion of heavy metals from the body depends on the presence of antioxidants. Antioxidants mitigate the harmful effects of free radicals.[5] Glutathione is of primary importance as an intracellular antioxidant, as in addition to being essential for cellular energy production and protection from oxidative damage, it also complexes with metals such as mercury and transports them out of cell and the body.[22],[23] GPx, one of the enzymes requiring selenium, facilitates the reaction between glutathione and hydrogen peroxide, generating oxidized glutathione and water.[24] The oxidized glutathione is then recycled back to reduced glutathione via another enzyme, glutathione reductase.

Studies show that selenium also works alongside antioxidant nutrients such as vitamins E and C, resveratrol, and isothiocyanates (sulforaphane) to reduce heavy metal toxicity.[25] A combination of sulforaphane and selenium has been shown to provide greater protection against oxidative injury than either ingredient alone.[26],[27] Sulforaphane is a type of organic compound known as isothiocyanate found in all those healthy cruciferous vegetables: broccoli, cabbage, kale, collard greens, cau­liflower, bok choy, and Brussels sprouts.[28] Sulforaphane works through Nrf2,[29] a protein that masterminds cellular responses to oxidative stress, upregulating enzymes necessary for glutathione recycling.[30] Nrf2 turns on the first step of gene expression of the redox managers TrxR-1 and GPx2, which utilize selenium and restore the redox balance – as long as enough selenium is around.[31]

Selenium and coenzyme Q10 (CoQ10), a fat-soluble antioxidant, work together to support heart health.[32] A prospective randomized double-blind placebo-controlled trial in Sweden showed a significant long-term reduction of cardiovascular mortality in elderly individuals supplemented with both CoQ10 (200 mg per day) and selenium (200 mcg per day) for up to five years, compared with a placebo group.[30] Remarkably, the health benefits of selenium and CoQ10 were still apparent 12 years later.[33] Further analysis showed that selenium supplementation was cardio-protective in participants with low serum selenium concentrations at the start of the study, while there was no effect of supplementation in those with adequate selenium (defined as a serum selenium level greater than 85 mcg/L).[34]

How much selenium do we need?

The U.S. recommended dietary allowance (RDA) of selenium for adults is 55 mcg (micrograms) per day.[35] The main dietary sources of selenium are Brazil nuts, seafood, meat, poultry, fish, eggs, and whole-grain bread.[33] Fruits and vegetables generally are low in selenium. If you – or someone you love – is on a vegan, gluten-free, or ketogenic diet, take note: such diets often provide suboptimal levels of selenium.[36],[37],[38],[39],[40]

Dietary supplementation of selenium at a dose of 200 mcg per day is generally considered safe and adequate for adults of average weight consuming a typical American diet.[41] Excessive selenium intakes are not beneficial, and may even produce harmful effects over the long term, including a possible increased risk of diabetes and amyotrophic lateral sclerosis (ALS).[42]

Summary

Selenium has a powerful role as a detox/redox agent. It helps protect the health of the body systemically against oxidative damage caused by a variety of environmental pollutants. Selenium supplementation at modest levels helps replenish selenium stores in the event of suboptimal diets and common environmental exposures, including heavy metals like mercury.

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