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The Facts About Selenium
No knowledge of antioxidants is complete without an introduction to the facts about selenium.
Selenium is a mineral found in many soils and rocks, and it is needed in trace quantities in the diet for good health. The major role of selenium in the body is that it forms part of important antioxidant enzymes called selenoproteins, which scavenge for free radicals and neutralize them.
Antioxidants are the body's defense against free radicals (oxidants), which are produced when the cells use oxygen to release energy from the food we eat. Free radicals are unstable molecules that damage DNA, protein, and fats if they are not neutralized. Once a free radical is produced in the cell it can set up a chain reaction, since a molecule attacked by the free radical can become a free radical in turn. This chain reaction can cause the death of the cell.
Free radicals are thought to be one of the major causes of diseases such as cancer and heart disease, and they have also been implicated in conditions such as cataracts, diabetes, rheumatoid arthritis, macular degeneration, Alzheimer's disease, osteoarthritis, and stroke.
Antioxidants neutralize free radicals, and since they are themselves neutralized by the reaction, we need a constant supply of new antioxidants. There are many kinds of antioxidants, such as vitamins A, E and C, and beta-carotenes, but among the most powerful are the enzymes containing selenium.
Selenoproteins are also essential elements of the immune system, and the number of immune cells increases when selenoproteins are present. They also protect the body against viruses. In fact if selenium levels are low, viruses have been shown to grow stronger and hardier in some people. Selenoproteins also play a role in regulating thyroid function, and some studies have found low blood selenium levels in rheumatoid arthritis patients, which means selenium may also protect against this condition. Low selenium levels have also been seen in cancer patients in several studies of different kinds of cancer.
In additon to knowing the facts about selenium, it's crucial to know where you can find it!
Selenium is obtained in the diet mainly from plants such as rice, corn, wheat and soy beans, but is also found in red meat, chicken, fish and eggs. Other good sources include brewer's yeast, wheat germ, butter, onions, garlic, and shellfish. Nuts (especially Brazil nuts) are also good sources of selenium in the Western diet. In fact the consumption of Brazil nuts should be limited because they contain extremely high levels of selenium.
The selenium content of foods depends on how rich in selenium the soil is where the plants and animals are grown. The soils of north Nebraska and the Dakotas have very high levels of selenium, whereas soils in parts of China and Russia are extremely low in selenium, leading to selenium deficiencies in these areas.
The major signs that you need more selenium in your diet include food and other allergies, frequent bouts of cold or flu, a metallic taste in the mouth, and any numbness in the extremities.
Throughout the world, many people suffer from selenium deficiency and don't even know it. How could they know it when they don't have the basic facts about selenium?
Severe selenium deficiency is rare outside of China and Russia, and for most people a healthy diet with a variety of fruits, vegetables, nuts and grains can easily provide ample selenium without supplements. Most cases of severe deficiency are associated with serious gastrointestinal problems such as Crohn's disease, surgical removal of part of the stomach, or iodine deficiency. Selenium deficiency causes the immune system to be run down, and makes the body more susceptible to illness. It can also cause a condition known as Keshan disease.
Supplementation may be recommended for people with HIV, since selenium has been shown to be beneficial for these patients. In fact, one study (by Baum and others) showed that HIV patients with low levels of selenium were almost 20 times more likely to die from HIV related conditions than those with good selenium levels, and that reduced selenium was a greater risk than deficiency in any other nutrient they looked at.
Taking large doses of selenium as a supplement is not recommended for generally healthy people because excessively high levels of selenium can result in the rare condition of selenosis, which causes fatigue, irritability, gastrointestinal upsets, skin rashes, bleached and brittle nails, hair loss, garlic breath smell, and mild nerve damage. As with all trace elements and minerals, the best approach is to aim to eat a wide variety of foods to ensure you are getting adequate amounts of all nutrients.
Now that you know the basic facts about selenium, you'll have a better understanding of how antioxidants work within your body, and you can take this knowledge further if you desire.
For more on the science and facts about selenium, check out the Wikipedia entry.
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