Selenium is an essential mineral found in trace amounts in the human body. It works as an antioxidant, especially when combined with vitamin E, by scavenging damaging particles in the body known as free radicals. These particles occur naturally in the body but can damage cell membranes, interact with genetic material, and possibly contribute to the aging process as well as the development of a number of conditions including heart disease and cancer. Antioxidants such as selenium can neutralize free radicals and may reduce or even help prevent some of the damage they cause.

Selenium is needed for the proper functioning of the immune system and for the production of prostaglandins (substances that affect blood pressure and inflammation in the body). Low levels of selenium may worsen atherosclerosis (plaque buildup in arteries which can lead to heart attack and/or stroke) and can lead to premature aging. Selenium deficiencies have also been linked with certain types of cancer.

Many of the benefits of selenium are related to its role in the production of the enzyme glutathione peroxidase. This enzyme is responsible for detoxification in the body. Chronic exposure to environmental toxins, including chemotherapy drugs, radiation and other toxic medicines, increases the requirement for selenium.

Cigarette smokers have lower levels of selenium. There are several reasons for this. Tobacco decreases absorption of selenium in the digestive tract. In addition, many smokers have poor dietary habits and eat fewer foods containing selenium. Alcohol also lowers selenium levels.

Heart Disease
Low blood levels of selenium can contribute to heart failure. Selenium deficiencies have been shown to worsen atherosclerosis (plaque build up in arteries which can lead to heart attack and/or stroke). It is not known, however, whether selenium supplementation can prevent development or progression of atherosclerosis. Plus, some researchers are concerned that selenium supplements may minimize the benefits of cholesterol lowering drugs.

Cancer
Several animal and human studies have suggested that selenium may protect against the development of colon cancer. Higher cancer rates have been observed in areas where the level of selenium in the soil is low. At least one study has also found that selenium may reduce the risk of death from colon cancer.

Similarly, population based trials suggest that people who eat a diet rich in antioxidants, including selenium, may reduce their risk of prostate cancer. The National Institutes of Health (NIH) is currently sponsoring a large clinical trial, with projections of over 32,000 male participants, to evaluate whether use of selenium and vitamin E helps prevent prostate cancer.

In another study, over 1,300 people with skin cancer were randomly assigned to receive either selenium 200 mcg per day or placebo for at least three years. The researchers found that people who were not taking selenium were more likely to develop lung, prostate, or colon cancers than those who did take the supplement. Plus, an animal study found that selenomethionine (an active breakdown product of selenium) may reduce the spread of melanoma cells in mice. The authors of this study suggest that selenomethionine may prove to be an appropriate addition to the standard treatment for melanoma.

More research is needed to evaluate the use of selenium in preventing and treating the types of cancers discussed in this section. Any potential relationship between selenium supplements and other types of cancer, such as breast and cervical, have not been thoroughly evaluated in studies. Use of selenium supplements in conjunction with other antioxidants (including vitamin C, vitamin E, beta-carotene, and coenzyme Q10) and essential fatty acids, may reduce cancer spread and lessen death rate in women with breast cancer. However, this benefit cannot be attributed to selenium alone.

Immune Function
Numerous studies suggest that selenium is necessary for proper immune function. Selenium along with other minerals can help build up white blood cells, enhancing the body's ability to fight illness and infection.

In a study of 725 elderly men and women, for example, those who received zinc and selenium supplements demonstrated a better immune response to the influenza vaccine than those who received placebo. These results suggest that selenium and zinc supplements may boost immunity in older people and improve their resistance to infections.

In addition, an animal study found that selenium deficiencies may cause the flu virus to mutate into more dangerous forms, leading to harmful lung inflammation.

Asthma
Evidence suggests that people with asthma tend to have low blood levels of selenium. In a study of 24 people with asthma, those who received selenium supplements for 14 weeks demonstrated a significant improvement in symptoms compared to those who received placebo. More studies are needed, however, to determine whether selenium supplementation is safe and effective for people with this respiratory condition.

HIV
Selenium plays a key role in the proper functioning of the immune system and studies have shown that levels of this nutrient decline consistently as HIV progresses. Preliminary evidence suggests that selenium supplementation may improve certain symptoms of this condition.

For example, severe weight loss is a serious problem for people with HIV. In a well-designed study of people with HIV, those who took a daily supplement containing selenium, glutamine, beta-carotene, N-acetylcysteine, and vitamins C and E for 12 weeks gained significantly more weight than those who took placebo. Given the number of nutrients included in this supplement, however, it is unclear whether it was the selenium alone or the combination of all nutrients that ultimately prevented the weight loss in the study participants.

Burns
When skin is burned, a substantial percentage of micronutrients, such as copper, selenium, and zinc may be lost. This increases the risk for infection, slows the healing process, prolongs the hospital stay, and even increases the risk of death. Although it is unclear which micronutrients are most beneficial for people with burns, many clinicians suggest that a multivitamin including selenium may aid in the recovery process.

Depression
Some reports indicate that selenium affects mood. In one study of people with low levels of selenium, those who consumed a diet high in selenium reported fewer feelings of depression after 5 weeks.

Male Infertility
Selenium and other antioxidants play an essential role in the formation of certain proteins found in sperm. Deficiencies of selenium, therefore, can have a detrimental effect on sperm motility. In a study of 69 infertile Scottish men, those given selenium or selenium in combination with vitamins A, C, and E for three months demonstrated significant improvement in sperm motility compared to men given placebo pills. Sperm count was unaffected.

Miscarriage and Female Infertility
Women who have miscarried tend to have lower levels of selenium than women who carry a pregnancy to full term. Whether selenium supplementation helps prevent miscarriage, however, is not clear. One study of only 12 women who either had trouble conceiving or had a history of miscarriage found that those who took selenium along with magnesium were more likely to carry their pregnancy to full term. Further research is needed. In the meantime, check your prenatal vitamin for selenium and magnesium content and talk to your doctor about the proper amounts

Diabetes
Animal studies suggest that selenium, particularly in combination with vitamin E, may lower blood sugar levels over time and reduce the risk of complications (such as kidney and blood vessel diseases) associated with diabetes. Studies in people are needed before conclusions can be drawn.

Inflammatory Bowel Disease (IBD)
People with inflammatory bowel disease (including Crohn's disease and ulcerative colitis) often have reduced levels of selenium, as well as other vitamins and minerals, in their bodies. In the case of IBD, this can be from decreased nutrional intake and absorption in the intestines, excessive diarrhea, and/or surgical resection of parts of the digestive tract. For this reason, a multivitamin including selenium may be recommended by health care professionals for people with this health condition.

Liver Disease
Low selenium levels may be associated with an increased risk for liver cancer in people with hepatitis B and/or C. Furthermore, low selenium levels may worsen the toxic effects of alcohol on the liver. It is not clear, however, whether selenium supplementation can help prevent or treat liver damage.

Disorders of the Pancreas
Studies have found that antioxidant therapy including selenium may significantly reduce pain in people with pancreatitis (inflammation of the pancreas).

Thyroid Problems
Selenium deficiency can affect metabolism of thyroid hormones. Selenium supplementation in a small group of elderly individuals improved thyroid function.

Skin Problems
Selenium supplementation may help improve symptoms in individuals with various skin conditions such as acne, psoriasis, and eczema.

Rheumatoid Arthritis
Low levels of selenium in the blood may be associated with increased risk of rheumatoid arthritis. It is not known, however, whether supplementation with selenium alone will improve arthritis. Some experts believe, however, that the combination of selenium and vitamin E helps relieve symptoms.

Other
Preliminary studies also indicate that selenium supplementation may be useful in the prevention and treatment of eye disorders (such as age-related macular degeneration) and lupus. Further studies are needed to confirm these findings, however.

Brewer's yeast and wheat germ, liver, butter, fish (mackeral, tuna, halibut, flounder, herring, smelts) and shellfish (oysters, scallops and lobster), garlic, whole grains, sunflower seeds, and Brazil nuts are all good sources of selenium.

The amount of selenium contained in different foods depends upon the level of selenium in the soil. Selenium deficiencies are common in parts of China and the U.S. where selenium levels in the soil are low.

Selenium is destroyed when foods are refined or processed. Therefore, eating a variety of whole, unprocessed foods is the best way to obtain this nutrient. This means eating foods in their original state, not canned, frozen, or commercially prepared.

Selenium may be taken as part of a vitamin-mineral supplement, a nutritional antioxidant formula, or as an individual supplement. Most supplements contain selenomethionine.

For best results, selenium should be taken with vitamin E.

The minimum daily recommended dietary allowances for selenium are listed below.

Pediatric

• Neonates to 6 months: 10 mcg
• Infants 6 months to 1 year: 15 mcg
• Children 1 to 6 years: 20 mcg
• Children 7 to 10 years: 30 mcg
• Males 11 to 14 years: 40 mcg
• Females 11 to 14 years: 45 mcg

The usual therapeutic dosage for children is considered to be 30 to 150 mcg, or 1.5 mcg per pound (0.7 mcg per kilogram) of body weight.

Adult

• Males 15 to 18 years: 50 mcg
• Males over 19 years: 70 mcg
• Females 15 to 18 years: 50 mcg
• Females over 19 years: 55 mcg
• Pregnant females: 65 mcg
• Lactating females: 75 mcg

Usual therapeutic dosage for adults is considered to be 50 to 200 mcg/day; but as dosages as high as 400 mcg/day may be recommended by a healthcare provider.

Because of the potential for side effects and interactions with medications, dietary supplements should be taken only under the supervision of a knowledgeable healthcare provider.

High doses of selenium (more than 1,000 mcg a day) over time may produce fatigue, arthritis, hair or fingernail loss, garlicky breath or body odor, gastrointestinal disorders, or irritability.

If you are currently being treated with any of the following medications, you should not use selenium supplements without first talking to your healthcare provider.

Cisplatin, Doxorubicin, and Bleomycin
Selenium may reduce toxic side effects associated with cisplatin and doxorubicin, two forms of chemotherapy used to treat cancer. On the other hand, a test tube study suggested that selenium may inhibit the anti-cancer effects of bleomycin.

Cholesterol-lowering Medications 
Researchers recently discovered an unexpected adverse interaction between antioxidant supplements and a popular combination of cholesterol-lowering medications known as simvastatin and niacin -- this interaction may have important implications for patients with heart disease. Together, simvastatin and niacin have been shown to lower LDL ("bad") cholesterol and raise HDL ("good") cholesterol in people with heart disease. When taken with antioxidants (including selenium), however, these medications may not be as effective in raising HDL cholesterol.

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