What Are Some Current Issues and Controversies About Selenium?

Selenium and cancer

Some studies indicate that mortality (death) from cancer, including lung, colorectal, and prostate cancers, is lower among people with higher selenium blood levels or intake. Also, the incidence of nonmelanoma skin cancer is significantly higher in areas of the United States with low soil selenium levels.

The effect of selenium supplementation on the recurrence of these types of skin cancers was studied in seven dermatology clinics in the US from 1983 through the early 1990s. Supplementation with 200 mcg selenium daily did not affect recurrence of skin cancer, but significantly reduced total mortality and mortality from cancers. In addition, incidence of prostate cancer, colorectal cancer, and lung cancer was lower in the group given selenium supplements.

However, not all studies have shown a relationship between selenium status and cancer. In 1982, over 60,000 participants of the Nurses Health Study with no history of cancer submitted toenail clippings for selenium analysis. Toenail analysis is thought to reflect selenium status over the previous year. After three and one-half years, researchers compared the toenail selenium levels of nurses with and without cancer. They did not find any apparent benefit of higher selenium levels.

These conflicting results emphasize the need for additional research on the relationship between selenium and chronic diseases such as cancer. A study that may help answer some of the questions about the effect of selenium supplementation on cancer risk has started in France. The Supplementation en Vitamines et Mineraux AntiXydants, or SU.VI.MAX Study, is a prevention trial that is providing doses of antioxidant vitamins and minerals that are one to three times higher than recommended intakes, including a daily supplement of 100 mcg selenium. More than 12,000 men and women are being followed for eight years to determine the effect of supplementation on the incidence of chronic disease, such as cancers and cardiovascular disease.

Selenium and heart disease

Some population surveys have indicated an association between a lower antioxidant intake with a greater incidence of heart disease. Additional lines of evidence suggest that oxidative stress from free radicals may promote heart disease. For example, it is the oxidized form of low-density lipoproteins (LDL, often called "bad" cholesterol) 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. Currently there is insufficient evidence available to recommend selenium supplements for the prevention of coronary heart disease.

Selenium and arthritis

Surveys of patients with rheumatoid arthritis, a chronic disease that causes pain, stiffness, swelling, and loss of function in joints, have indicated that they have reduced selenium levels in their blood. In addition, some individuals with arthritis have a low selenium intake.

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 control levels of free radicals and help to relieve symptoms of arthritis. Current findings are considered preliminary, and further research is needed before selenium supplements can be recommended for individuals with arthritis.

Selenium and HIV

HIV / AIDS related malabsorption can deplete levels of many nutrients. Selenium deficiency is commonly associated with HIV / AIDS, and has been associated with a high risk of death from this disease. Of 24 children with HIV who were observed for five years, those with low selenium levels died at a younger age, which may indicate faster disease progression. An examination of 125 HIV positive men and women also associated selenium deficiency with mortality. Researchers believe that selenium may be important in HIV disease because of its role in the immune system and as an antioxidant. Selenium also may be needed for the replication of the HIV virus, which could deplete host levels of selenium. Researchers are actively investigating the role of selenium in HIV / AIDS, and see a need for clinical trials that evaluate the effect of selenium supplementation on HIV disease progression.

________________________

Provided by the NIH Office of Dietary Supplements email: ods@nih.gov