Selenium is an essential trace mineral that the human body requires in small amounts. The cells incorporate selenium into proteins to form selenoproteins, a powerful antioxidant that prevents the kind of cellular damage that occurs from the normal processes of metabolism and energy production. Antioxidants can also help prevent the development of chronic diseases such as cancer and heart disease.
Melanoma
Melanoma is the most fatal form of skin cancer due to the rate at which it spreads. The primary cause is DNA damage from UV radiation which affects the melanocytes, a type of pigment-producing cell that gives the skin and eyes their color. Since the 1960s researchers have studied the efficacy of selenium, because of its antioxidant properties, on the incidence of cancerous tumors. Some evidence from the tumors in breast cancer suggests that selenium aggregates at the site of disease to fight the cancerous cells.
Evidence
Blood selenium levels appear to be lower in patients with melanoma compared with healthy individuals; patients in stage 3 of the disease had the lowest levels. This means that the consumption of selenium may help reduce the incidence of cancer. In 2009 a group of researchers from the University College of Medicine in Korea published a paper in the journal "Immune Network" that suggests selenium can inhibit the spread of melanoma cells by arresting the normal cell cycle and causing the death of the cancerous cells. Another study published in a 2008 issue of "Molecular Cancer Therapeutics" by researchers from Penn State University College of Medicine found that a novel selenium-containing drug is also effective at inhibiting the spread of melanoma cells.
Dietary Sources
The amount of selenium in food depends upon the selenium content in the soil. Plants grown in soil with high selenium levels, and the animals that eat those plants, tend to have the most selenium. Good sources include Brazil nuts, beef, turkey, chicken, oatmeal, rice, bread, pasta and certain fish such as tuna and cod. The recommended dietary allowance for adults 19 years and older is only 55 micrograms a day --- though pregnant and lactating women need 60 and 70 micrograms, respectively. However, too much selenium in the blood is toxic and may cause hair loss, fatigue, irritability, nerve damage and gastrointestinal problems. The safe upper limit is 400 micrograms per day, though consumption can conceivably reach 800 micrograms per day before any serious effects occur.
Increased Risks
Some researchers have expressed concern that excessive selenium, because of its toxic effects, may actually increase the risk of melanoma, for example, in people who take dietary supplements. The evidence so far has been conflicting. One 2009 study in the "Archives of Dermatology" assessed these risks in 69,671 men and women and did not find an association, repudiating an earlier study that claimed to observe an increased risk in women. Future research is required to arrive at a more definitive conclusion.
References
- Office of Dietary Supplements: Selenium
- "Acta Dermato-Venereologica"; Serum Selenium Levels in Patients with Malignant Melanoma; U. Reinhold, et al.; 1989
- "Immune Network"; Selenium Inhibits Metastasis of Murine Melanoma Cells through the Induction of Cell Cycle Arrest and Cell Death; H. Song, et al.; December 2009
- "Molecular Cancer Therapeutics"; PBISe, a Novel Selenium-Containing Drug for the Treatment of Malignant Melanoma; SubbaRao V. Madhunapantula, et al.; May 2008
- Kaiser Permanente; Antioxidants Not Associated With Increased Melanoma Risk; August 2009
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