Selenium in a nutshell:
Selenium is an antioxidant, but it has very important roles in the conversion of thyroid hormone T4 into the active T3 form.
Best source of selenium for Juicers
Selenium is found in chard, turnips, garlic, oranges, radishes, carrots & cabbage.
Selenium is an ultratrace mineral that we need in just millionths of a gram. Getting enough selenium assists in recovery from numerous health conditions, but getting too much selenium causes its own problems.
Alternative names: Selenium; selenides, selenates, and selenites (inorganic selenium, toxic in small doses); selenocysteine and L-(+)-selenomethionine (selenium from natural sources, toxic in large doses but nutritional in small doses).
What Is Selenium?
Selenium is an element from the sulfur family of elements. Unlike most mineral elements, it can form chemical bonds directly with carbon, fundamentally changing the structure of an organic molecule rather than just changing the way it reacts with other mineral salts. Pure selenium almost never occurs in nature, but when it does, it forms hair-like black crystals. Most of the selenium in the earth's crust is found in iron or copper ores or in combination with lead.
Selenium can also form compounds with sulfur. They can leach out of rocks into the soil during rainstorms and floods, and they can concentrate in the soil at the bottom of lagoons and lakes. Certain plants concentrate selenium in either nutritional amounts, but certain grasses and weeds concentrate selenium in toxic amounts.
What Does Selenium Do in the Human Body?
Nutritionists usually describe selenium as an antioxidant. A chemical compound of selenium and the amino acid cysteine, selenocysteine, helps to recharge the antioxidant glutathione peroxidase. Selenocysteine converts potentially damaging hydrogen peroxide (H2O2) into water (H2O). While it is possible to survive without either selenocysteine or glutathione peroxidase, but this selenium compound and the antioxidant for which it is a cofactor prolong life.
The really essential functions of selenium in the human body, however, do not involve antioxidants. In the forms of methylselenium and S-methyselenocysteine, selenium performs other essential functions.
- Selenium partially deactivates the gene that contains the code for the creation of a substance known as NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells). This substance activates inflammatory responses to stress, oxidized LDL cholesterol, viral infections, bacterial infections, and UV radiation. Having enough selenium helps keep inflammation from destroying healthy tissue, but having too much selenium prevents inflammation from removing damaged or cancerous tissue.
- Selenium activates certain genes that are involved in “growth arrest” of cells with damaged DNA. Some of these genes trigger a process called apoptosis, or “cellular suicide,” in certain kinds of cancer cells. Others keep cells with DNA damage from reproducing themselves.
- Selenium may substitute for sulfur in the creation of an enzyme called tyrosine kinase. This enzyme turns genes “on” and “off.” It is critical for ensuring that cells multiply only as often as needed. Mutations of this enzyme are a major cause of certain kinds of cancer, especially leukemia. Selenium sometimes “mutates the mutation” so that tyrosine kinase works properly.
The most important role of selenium in the human body, however, is in the activation of thyroid hormone. Thyroid hormone is essential for activating metabolic processes all over the body, but it has to be converted from a storage form of the hormone, T4, which contains four atoms of iodine into an active form of the hormone, T3, which contains three atoms of iodine. Tissues all over the body accomplish this with an enzyme known as iodothyronine deiodinase, or ID. The enzyme “grapples” T4 at a fold in its molecular structure that uses the selenium compound selenocysteine as a kind of molecular glue. The conversion enzyme can function even without selenium, but only about 10% as efficiently.
Active thyroid hormone is essential for life. Selenocysteine isn't—but losing 90% of the effects of active thyroid hormone can make the body very sick.
What Happens When We Don't Get Enough Selenium?
Selenium deficiency is a well-known health problem. In some parts of the world, the soil contains enough selenium for native plant and animal life but not enough selenium to grow plants to feed humans. In Keshan county in the province of Heilongjiang in far northeastern China, the soil lacks selenium. Many people who live in the county suffer a condition known as Keshan disease, which can occur even in infants.
In Keshan disease, the lack of selenium interferes with the heart's ability to make an enzyme called thioredoxin reductase. This enzyme protects growing heart tissue from free radicals of oxygen. Sometimes children are born with heart defects because free radicals of oxygen attack the developing heart even while the child is still in utero. In selenium-deficient people who survive childhood, the risk of lasting heart damage from viral diseases of the heart is much greater because the heart does not have the enzymes that protect it from free radicals of oxygen generated as the heart is healing.
In the provinces Tibet and Sichuan, in southwestern China, and in parts of North Korea, soils are deficient both selenium and iodine (at least from the point of view of supporting agriculture). People in Sichuan and Tibet and parts of North Korea are at elevated risk for a condition known as Kashin-Beck disease, some villages having up to 90% of children affected. In this condition, the lack of both selenium and iodine causes joint problems, especially an inability to squat (which is essential for many life activities in China, ranging from using the toilet to participating in sharing a cup of tea). Up to 1/3 of people who have Kashin-Beck disease cannot walk and another 1/3 walk only with difficulty. The combination of selenium and iodine deficiency causes damage to the joints that receive the least oxygen supply, those that are covered by the largest muscles.
People who eat food grown on selenium-deficient soils in Africa tend to develop goiter, due not to a deficiency in iodine but an inability to convert iodine from T4 to T3. People who eat food grown on selenium-deficient soils in Uruguay tend to be at greater risk for multiple organ failure later in life.
Selenium-deficient soils also occur in some parts of Finland. In Finland, selenium deficiency most often expresses itself as rheumatoid arthritis. Finnish researchers have made extensive studies of the benefits of selenium supplements, finding that selenium from organic sources (for instance, yeast or wheat grown on selenium-rich soils) is much more effective than selenium from industrial sources (for example, sodium selenate).
Are You at Risk for Selenium Deficiency?
If you have spent a large part of your life in sub-Saharan Africa, in North Korea, Uruguay, certain parts of Finland, or in Keshan, Sichuan, or Tibet, you may indeed benefit from selenium and/or iodine supplementation. But if you have lived most of your life in other parts of the world, chances are you are not selenium-deficient.
Certain chronic health conditions, however, are a signal of subclinical selenium deficiency. You may not suffer Keshan disease or Kashin-Beck disease, but you may not be receiving enough selenium for good health if:
- You have Crohn's disease, inflammatory bowel disease, or ulcerative colitis.
- You suffer from chronic constipation.
- You have been diagnosed with hypothyroidism.
It's also possible that selenium deficiency is an issue for you if you suffer some of the signs of “subclinical” hypothyroidism:
- You are easily fatigued.
- You are unusually sensitive to cold.
- Your skin is dry.
- Your hair is dry, coarse, or thinning.
- You tend to be constipated.
- You gain weight more easily than you used to.
- Your short-term memory isn't up to par.
- Your eyelids, fingers, or feet tend to swell (and the skin springs back when you depress it).
- Your reflexes have slowed down.
- You get laryngitis even when you don't have a cold or sore throat.
- Your hearing isn't what it used to be.
- Your heart rate is slow.
- Your cholesterol levels are sometimes high, and sometimes normal or even low.
Most doctors test for thyroid stimulating hormone (TSH) and the inactive form of thyroid hormone known as T4. But your TSH and T4 levels can be normal and you may still have symptoms of hypothyroidism if you have low levels of T3, the active form of thyroid hormone. If you have normal or even high T4 but low T3, you may need selenium supplementation. Just one word of caution: Receiving more than 350 micrograms of selenium per day may actually interfere with the conversions of T4 to T3.
How You Can Be Sure of Getting Enough Selenium
The Recommended Dietary Allowance (RDA) for selenium is measured in micrograms, millionths of a gram. In 2000 the Food and Nutrition Board of the Institute of Medicine set RDAs for selenium as follows:
- Infants up to 6 months of age should receive 15 micrograms per day.
- Infants 6 to 12 months of age and toddlers aged 1 to 3 should receive 20 micrograms per day.
- Children aged 4 to 8 should receive 30 micrograms per day.
- Children aged 9 to 13 should receive 40 micrograms per day.
- Teens between aged 14 to 18 and most adults should receive 55 micrograms per day.
- Women who are pregnant should receive 60 micrograms per day.
- Women who are breastfeeding should receive 70 micrograms per day.
It's easy to prevent selenium deficiency if you can eat Brazil nuts. A single serving of Brazil nuts (6 kernels) grown on selenium-rich soils contains about 550 micrograms of selenium, more than a week's supply. Most ocean-caught sea foods provide 30 to 40 micrograms of selenium per 3-1/2 ounce (100-gram) serving. In the United States and Canada, vegetables tend to be grown on selenium-deficient soils but grains tend to be grown on selenium-sufficient soils, but most Americans and Canadians eat foods grown all over their countries and get enough selenium in their diets.
People in the rest of the world are more likely to get their selenium from sea food, whole grains, beef, pork, or poultry. No matter where you live in the world, broccoli sprouts (sprouted broccoli seed), barley sprouts (sprouted barley seed, usually dried as used as a tea), wheat grass (shoots from sprouted wheat), and ramps (wild leeks) are usually good sources of selenium.
The Chinese medicinal herb astragalus root is extremely rich in selenium. Up to 1% of the dried herb is selenium. Just 1 gram of the root contains 1,000 to 10,000 micrograms of selenium. For that reason, you should not use astragalus on a regular basis (for more than one week) even if directed by a practitioner of Traditional Chinese Medicine, and you should use astragalus capsules and over-the-counter formulas that contain astragalus with extreme caution, staying aware of the symptoms of toxic overdose.
What About Selenium Supplements?
It's important not to take more than 100 micrograms of selenium per day. Selenite supplements are only about 50% absorbed, and they should not be taken at the same time as vitamin C. Selenate supplements are nearly 100% absorbed, but the body excretes about 50% of them into the urine before they can be used to make enzymes and proteins. Selenomethionine, the form of selenium found in food, is about 90% absorbed and retained by the body. Selenomethionine is the best choice among selenium supplements, although some “natural” selenomethionine supplements actually contain the artificial form of selenium, selenite.
Don't take too much selenium. Selenium poisoning is rare but possible. Usually the problem is due to the way a supplement is manufactured, a formulator confusing micrograms (millionths of a gram) with milligrams (thousandths of a gram) and putting 1,000 times too much selenium in a product.
Taking more than 850 micrograms of selenium per day over a period of weeks or months causes a predictable pattern of symptoms of toxicity:
- Garlic breath even when garlic is not eaten.
- Brittle fingernails and vertical lines on the fingernails.
- Hair loss.
- Muscle cramps.
- Diarrhea, bloating, and/or acid reflux.
- Joint pains.
- Blistering skin.
For all the applications listed below, it's best to take at most 200 micrograms of selenomethionine per day—no more. If you develop any of the symptoms listed above (they will usually develop in just 5 to 10 days), discontinue taking your supplement and check FDA Medwatch online to see if it has been recalled.
Using Selenium to Prevent Cardiovascular Disease
When selenium is deficient, the heart and arteries cannot make enzymes that regulate how they respond to LDL cholesterol and that protect them against the effects of low oxygen levels. Selenium compounds are involved in how the heart uses ubiquinone, also known as coenzyme Q10 or CoQ-10. While it's important to avoid deficiency, there is no evidence that taking more selenium than is needed to prevent deficiency will additively strengthen the heart or blood vessels.
Using Selenium to Prevent Breast Cancer
Selenium compounds activate the “cancer watchdog” gene p53. This gene is important helps control breast and colon cancer by initiating the process of “cellular suicide” known as apoptosis in cancer cells. Although there is no evidence that taking selenium cures breast cancer, avoiding selenium deficiency may help prevent it.
Using Selenium to Prevent Type 2 Diabetes
Getting enough selenium also seems to reduce the risk of developing type 2 diabetes as an adult. Consuming 200 micrograms of selenium per day or more, however, actually increases the risk of developing type 2 diabetes as an adult.
Using Selenium to Prevent Esophageal Cancer
The Chinese province of Linxiang has the highest rates of esophageal cancer in the world, and it is also a location in which most people receive insufficient selenium from their diets. A study in which people were given 200 micrograms of supplemental selenium per day resulted in a 13% reduction in the rate of esophageal cancer. Selenium does not, however, treat esophageal cancer once it develops.
Using Selenium to Prevent the Progression of Hepatitis B to Liver Cancer
Medical researchers working in the Chinese province of Qidong found that giving just 35 to 50 micrograms of supplemental selenium every day resulted in a 50% reduction in the rate of liver cancer. Most people in Qidong who develop liver cancer are previously infected with hepatitis B.
Using Selenium to Prevent the Progression of HIV to AIDS
HIV is a virus that multiplies more rapidly in the presence of free radicals of oxygen. Glutathione peroxidase prevents the creation of free radicals of oxygen, and selenium is important in making glutathione peroxidase. Indirectly, getting enough selenium may help keep viral load of HIV in check.
The problem with using selenium to support health in HIV is that the virus itself can also use selenium to make its own antioxidant enzymes. The optimal form of selenium for people with HIV or AIDS is selenomethionine and the optimal dosage is 80 to 200 micrograms per day. It's important to discuss the possible interactions of selenium with HIV drugs and to make arrangements to track changes in T-cell count, viral load, and AIDS symptoms before beginning supplementation with selenium or any other nutrient.
Using Selenium to Prevent Osteoporosis
Vitamin K is essential for normal mineral metabolism in healthy bones. Selenium helps regulate vitamin K3. Preventing selenium deficiency is probably essential to preventing osteoporosis, although taking selenium may not be helpful once osteoporosis has already occurred.
Using Selenium to Prevent Thyroid Cancer
In one study of men who had thyroid cancer, the disease was found to be associated with high levels of cobalt, mercury, rubidium, and silver in the bloodstream and low levels of selenium in the bloodstream. Men who had the lowest bloodstream levels of selenium were nearly 8 times more likely to develop thyroid cancer than men who had the highest bloodstream levels of selenium. While selenium will not cure thyroid cancer, preventing selenium deficiency may help prevent it.
Using Selenium to Treat Rheumatoid Arthritis
One clinical trial found that taking 200 micrograms of selenium per day for 3 months relieved joint pain. There seem to be upper limits to the benefits of selenium supplementation, however. A follow-up study did not find significant benefits of taking selenium for a second 3-month period. In other words, one bottle of selenium supplements helps, but two won't do any additional good.
Using Selenium to Treat Asthma and Chronic Obstructive Pulmonary Disease (COPD)
Some studies have found that fewer children develop asthma where the diet is richer in selenium. Studies of selenium as a treatment for asthma and COPD find benefits when it is taken for 1 to 2 years. In one study, taking 200 micrograms of selenium everyday reduced inhaler use after six months and reduced overall use of medication after one year. There may be a point at which additional selenium supplementation is of no further benefit but studies have not been run that long.
Using Selenium to Treat Male Infertility
Along with B vitamins and zinc, selenium has been used to treat male infertility. Selenium seems to be helpful for sperm motility, the measure of sperm's “swimming ability.” More selenium, however, is not necessarily better. In one trial, men with fertility issues were given 47 micrograms of selenium for 21 days, and then either 13 micrograms per day or 297 micrograms per day. The men who were given the lower dose of selenium after the first 21 days had greater increases to fertility.