About Selenium

Selenium and Methylselenocysteine

Selenium is an essential trace mineral that is essential for life. It is also a toxic metal when consumed in excess. Selenium is required to activate various key enzymes, including the antioxidant glutathione peroxidase, the metabolic enzyme thioredoxin reductase, and the thyroid-hormone-activating enzyme iodothyronine deiodinase. Food sources of selenium include brazil nuts, yeast, whole grains and seafood. Selenium content of food is dependent on selenium content in the soil and both are highly variable.
Selenium: The Anticancer Mineral

Epidemological studies recognized a connection between cancer incidence and low levels of selenium in the blood as early as 1969. Researchers noted that breast cancer rates were low in areas where selenium levels in the soil and food were high and high in areas where selenium levels were low. The same correlation was found between death rates and selenium levels. Similar correlations were subsequently found in animal studies.
Helps in treatment and prevention of dandruff. Necessary for healthy hair and nails. May also increase the elastic youthfulness of the skin and be helpful in removing age spots. When ingested in the natural algae form of selenomethionine, skin cancer incidence from ultraviolet light may also be reduced.
Selenium (Se) is an essential trace element that functions as a component of enzymes involved in antioxidant protection and thyroid hormone metabolism. In several intra- and extra-cellular glutathione peroxidases, iodothyronine 5н-deiodinases, and in thioredoxin reductase, selenium is located at the active centers as the selenoamino acid, selenocysteine (SeCYS). At least two other proteins of unknown function also contain SeCYS. Although SeCYS is an important dietary form, it is not directly incorporated into these specific selenium-proteins; instead, a co-translational process yields tRNA-bound SeCYS. In contrast, selenium as seleno-methionine is incorporated non-specifically into many proteins, as it competes with methionine in general protein synthesis. Therefore, tissues often contain both specific, as well as the nonspecific, selenium-containing proteins when both SeCYS and selenomethionine are consumed, as found in many foods.

IMPORTANCE: A major antioxidant nutrient, protects cell membranes and prevents free radical generation thereby decreasing the risk of cancer and disease of the heart and blood vessels. Medical surveys show that increased selenium intake decreases the risk of breast, colon, lung and prostate cancer. Selenium also preserves tissue elasticity; slows down the aging and hardening of tissues through oxidation; helps in the treatment and prevention of dandruff.

Deficiencies: Selenium deprivation reduces activities of the selenium-dependent enzymes. The signs in animals depend upon vitamin E status and appear only when both nutrients are limiting. They vary according to species. For example, selenium- and vitamin E-deficient animals show myopathies of skeletal (e.g., sheep, cow, horse), cardiac (pig) or smooth (dog, cow) muscle; hepatic necrosis (rat, pig); increased capillary permeability (chicken); or pancreatic acinar degeneration (chicken). Characteristic signs of selenium deficiency have not been described in humans, but very low selenium status is a factor in the etiologies of a juvenile cardiomyopathy (Keshan Disease) and a chondrodystrophy (Kashin-Beck Disease) that occur in selenium-deficient regions of China. May result in premature aging, heart disease, dandruff, loose skin.

Diet recommendations: The Recommended Dietary Allowances are in µg/day: 0-0.5 yrs, 10; 0.5-1.0 yrs, 15; 1-6 yrs, 20; 7-10 yrs, 30; males 11-14 yrs, 40; females 11-14 yrs, 45; males and females 15-18 yrs, 50; adult males, 70; adult females, 55; pregnancy, 65; and lactation, 75.

Food sources: The most important sources in American diets are meats, fish and grains. Brazil nuts can have relatively high selenium concentrations. Foods of low protein content, including most fruits and vegetables, provide little selenium. Food selenium is absorbed with efficiencies of 60-80%; the greatest factor affecting the utilization of food selenium is its chemical form.

In humans, it has been observed that a 200 mcg daily supplement given for four years led to a significant reduction in cancer deaths and reduction in the incidence of prostate, lung, colorectal and some types of skin cancer. The control group received 85 mcg per day in their diet. It has also been observed that the known selenoenzymes are saturated with 90 mcg daily of selenium. This indicates that an additional anticancer mechanism is in play in addition to the antioxidant activity of selenium.
Selenium and heart disease

Epidemiological data suggests an association between lower antioxidant intake and a greater incidence of heart disease. Evidence also suggests that oxidative stress from free radicals may promote heart disease. It is the oxidized form of low-density lipoproteins (LDL) that promotes plaque build-up in coronary arteries. Selenium is one of a group of antioxidants that may help limit the oxidation of LDL cholesterol and thereby help to prevent coronary artery disease.
Selenium and Arthritis

Epidemiological data indicates that individuals with rheumatoid arthritis have reduced selenium levels in their blood. The body’s immune system naturally makes free radicals that can help destroy invading organisms and damaged tissue, but that can also harm healthy tissue. Selenium, as an antioxidant, may help to relieve symptoms of arthritis by controlling levels of free radicals.
Recommended Daily Intake of Selenium:

The Institute of Medicine has established a Recommended Dietary Intake for selenium. The RDA is the average daily intake that the Institutes of Medicine believe is sufficient for the nutrition needs of approximately 97% of the population.

* Children 1-3 years – 20 mcg
* Children 4-8 years – 30 mcg
* Children 9-13 years – 40 mcg
* Males 14-18 – 55 mcg
* Females 14-18 – 55 mcg
* Males 19+ – 55 mcg
* Females 19+ – 55 mcg
* Males 50+ – 55 mcg
* Females 50+ – 55 mcg
* Pregnant females – 60 mcg
* Lactating females – 70 mcg

The Institute of Medicine has also established upper tolerable intake levels for selenium. Those levels are established for supplements that carry a risk of toxicity at high levels. While selenium toxicity is rare, there is a condition called selenosis that results from excessive levels of selenium in the blood. The established upper levels for selenium are:

* Children 1-3 y – 90 mcg
* Children 4- 8 – 150 mcg
* Children 9-13 – 280 mcg
* Males 14-18 – 400 mcg
* Females 14-18 – 400 mcg
* Males 19+ – 400 mcg
* Females 19+ – 400 mcg

Symptoms of Selenium Deficiency:

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People in areas where the soil is depleted of selenium may be at risk of selenium deficiency. Individuals with absorption issues and certain disease states like AIDS may be deficient in selenium as well. The symptoms of selenium deficiency include hypothyroidism, a weakened immune system and heart disease.

Selenium Toxicity

Selenium toxicity is characterized by dermatologic lesions; selenotic animals and humans develop brittle hair and nails/hooves. Sporadic cases of selenium-poisoning have been reported involving industrial or accidental exposures to selenium-compounds. In certain rural Chinese communities chronic intakes of very high amounts (several milligrams per day) of selenium were linked to skin, hair and nail abnormalities which disappeared upon resuming regular selenium intakes. Selenium has been identified as the cause of birth deformities in migratory wildfowl in a wetland area (Kesterson Reservoir, CA) which receives selenium-enriched irrigation wastewater. This case involved the biological amplification of selenium by aquatic plants which were important in the diet of affected animals. The Reference Dose (RfD) set by the Environmental Protection Agency is 5 µg/kg body weight/day or 350 µg/day for a 70 kg individual. This intake is regarded as having no significant risk of a deleterious effect over a lifetime of exposure.

Researchers observed that the most powerful selenium anticancer effects often occurred at doses not far below the potentially toxic doses. This led to the study of the biochemistry of selenium’s anticancer action in more detail, in an attempt to surmount the potential toxicity problem.

Researchers have noted that organic forms of selenium are toxic at levels in the vicinity of 3,500 micrograms (3.5 milligrams) daily while Inorganic forms of selenium may be toxic at 900 mcg per day. Researchers have also noted that the various peoples around the world routinely get 400 to 600 mcg selenium from their diet, and Greenlanders may ingest as much as 1,300 mcg daily, without apparent ill effects. It has been observed that selenium (as high selenium yeast) is safe at both 200 and 400 mcg/day levels, even when taken for years.
Different Forms of Selenium

Inorganic forms of selenium such as sodium selenite have proven more effective at fighting cancer than the commonly used organic form, selenomethionine, yet selenomethionine was more effective at increasing selenium tissue levels and glutathione peroxidase activity. Because cells cannot distinguish selenomethionine from the essential amino acid methionine, some selenomethionine becames incorporated into general body proteins, increasing tissue selenium levels.

Selenomethionine general proteins have no anticancer activity while sodium selenite is more frequently metabolized to the toxic metabolite hydrogen selenide (H2Se). Hydrogen selenide does have anticancer effects but it is more toxic than selenomethionine. Its primary mode of killing cancer cells (and at high levels, normal cells) is through the process of cell necrosis. Cell necrosis provokes inflammation and may kill healthy cells along with cancer cells.

More recent anticancer research has focused on the compound Methyselenocysteine. Methyselenocysteine is found naturally in some vegetables including garlic, brassicas, leeks, and onions, especially when these are grown in high selenium soil. Methylselenocysteine is easily converted to methylselenol which has been demonstrated to be an effective anticancer form of selenium. Rather than killing cancer cells by necrosis, methylselenol kills cancer cells through apoptosis. Apoptosis is a orderly process of cellular self-destruction that does not provoke inflammatory responses. Methylselenol is also known to inhibit angiogenesis in beginning cancer tumors. Angiogenesis, the creation of new blood vessels, is necessary for cancer cells to grow into a tumor.

Methylselenocysteine does not accumulate in the body and is considered to be non-toxic.

Selenium and Methylselenocysteine Dosage

The RDA (Recommended Dietary Allowance) has been set at 55 mcg. for an adult. This is the intake level required to avoid manifesting obvious defeciency disorders and symptoms. The selenoenzymes have optimum selenium levels at around 90 mcg per day. For cancer prevention, doses of 200 to 400 mcg of methylselenocysteine are generally considered safe without medical supervision. Nutritionally-oriented physicians may use as much as 900 to 2,000 mcg selenium from methylselenocysteine daily as part of a comprehensive cancer treatment protocol.
Selenium Drug Interactions

Certain medications may interact with Selenium. Consult with your physician and pharmacist if taking medication and before taking more than an RDA dosage of selenium. Look up your medications in the Physician’s Desk Reference and check for interactions listed there.


Selenium – 200 mcg/day, as selenomethionine, 1 tablet (8 cents/day)

Bound to cysteine in place of sulfur and called the “21st amino acid,” selenocysteine is the active site in some 35 proteins. Glutathione peroxidase, which contains four selenium atoms, plays a major role in free radical defense. Plasma selenoprotein P protects endothelial cells against damage, and epithelial selenoprotein protects prostratic secretory cells from developing carcinoma. People deficient in selenium have an increased risk of cancer. Selenium prevents cancer through a variety of mechanisms, which include antioxidant protection, enhanced immune surveillance, suppression of angiogenesis, regulation of cell proliferation, enhancement of apoptosis (cell death), and inhibition of tumor cell invasion. See my article on selenium titled “The Moon Goddess’ Role in Human Health.”

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