What Is It
A trace mineral essential for many body processes, selenium is found in soil. In the body, selenium is present in virtually every cell but is most abundant in the kidneys, liver, spleen, pancreas, and testes.
What Does It Do
Selenium acts as an antioxidant, blocking the rogue molecules known as free radicals that damage DNA. It's part of an antioxidant enzyme (called glutathione peroxidase) that protects cells against environmental and dietary toxins, and is often included in antioxidant "cocktails" with vitamins C and E. This combination may help guard against a range of disorders, from cancer, heart disease, cataracts, and macular degeneration to strokes and even aging, thought to be caused by free-radical damage.
- Works with vitamin E to help prevent cancer and heart disease.
- Protects against cataracts and macular degeneration.
- Fights viral infections; reduces the severity of cold sores and shingles; may slow the progression of HIV/AIDS.
- Helps relieve lupus symptoms.
Selenium has received a lot of attention recently for its role in combating cancer. A dramatic five-year study conducted at Cornell University and the University of Arizona showed that 200 mcg of selenium daily resulted in 63% fewer prostate tumors, 58% fewer colorectal cancers, 46% fewer lung malignancies, and a 39% overall decrease in cancer deaths. In other studies, selenium showed promise in preventing cancers of the ovaries, cervix, rectum, bladder, esophagus, pancreas, and liver, as well as against leukemia. Studies of cancer patients indicate that people with the lowest selenium levels developed more tumors, had a higher rate of disease recurrence, a greater risk of cancer spreading, and a shorter overall survival rate that those with high blood levels of selenium.
Additionally, selenium can protect the heart, primarily by reducing the "stickiness" of the blood and decreasing the risk of clotting - in turn, lowering the risk of heart attack and stroke. Moreover, selenium increases the ratio of HDL ("good") cholesterol to LDL ("bad") cholesterol, which is critical for a healthy heart. Smokers or those who've already had a heart attack or stroke may gain the greatest cardiovascular benefits from selenium supplements, though everyone can profit from taking selenium in a daily vitamin and mineral supplement.
Selenium may be useful in preventing cataracts and macular degeneration, the leading causes of impaired vision or blindness in older Americans. It is also vital for converting thyroid hormone, which is needed for the proper functioning of every cell in the body, from a less active form (called T4) to its active form (known as T3). In addition, selenium is essential for a healthy immune system, assisting the body in defending itself against harmful bacteria and viruses, as well as cancer cells. Its immune-boosting effects may play a role in fighting the herpes virus that is responsible for cold sores and shingles, and it is also being studied for possible effectiveness against HIV, the virus that causes AIDS.
When combined with vitamin E, selenium appears to have some anti-inflammatory benefits as well. These two nutrients may improve chronic conditions such as rheumatoid arthritis, psoriasis, lupus, and eczema.
How Much You Need
The RDA for selenium is 70 mcg for men, and 55 mcg for women daily. To produce major benefits, up to 600 mcg a day may be needed.
If You Get Too Little:
Most Americans consume enough selenium in their daily diet, so deficiencies are rare. Falling below the RDA, however, may lead to higher incidences of cancer, heart disease, immune problems, and inflammatory conditions of all kinds, particularly those affecting the skin. Insufficient amounts of selenium during pregnancy could increase the risk of birth defects (especially those involving the heart) or, possibly, sudden infant death syndrome (SIDS). Early symptoms of selenium deficiency include muscular weakness and fatigue.
If You Get Too Much:
It's hard to get to much selenium from your diet, but if you're taking this mineral in supplement form, it's important to remember that the margin of safety between a therapeutic dose of selenium (up to 600 mcg a day) and a toxic dose (as little as 900 mcg) is small compared with other nutrients. Symptoms of toxicity include nervousness, depression, nausea and vomiting, a garlicky odor to the breath and perspiration, and a loss of hair and fingernails.
How To Take It
Most experts agree the optimum dose for long-teerm use of selenium should fall between 100 mcg and 400 mcg daily. Up to 600 mcg daily may be taken for a limited time as a treatment for viral infections or as part of a cancer treatment program.
Guidelines For Use:
Vitamin E greatly enhances selenium's effectiveness; be sure that you get 400 IU of it daily.
The most abundant sources of selenium include Brazil nuts, seafood, poultry, and meats. Grains, particularly oats and brown rice, may also have significant amounts, depending on the selenium content of the soil in which they were grown.
Don't exceed recommended doses: In some people, taking selenium long term (as little as 900 mcg a day) can cause serious side effects, such as skin rashes, nausea, fatigue, hair loss, fingernail changes, and depression.
- Recent studies show that in the test tube selenium works relatively quickly, helping cells grow and die at normal rates and protecting them from becoming cancerous. Experts suspect that selenium's cancer-fighting benefits may be fairly fast-acting in the body as well.
- According to the journal Agriculture Research, studies in mice show that a deficiency in either selenium or vitamin E both antioxidants - can convert a latent, inactive virus into its active, disease-causing form. This may help explain why selenium is effective against cold sores and shingles, which are both caused by reactivation of a dormant herpes virus.