Selenium is a trace mineral and an essential nutrient in the human diet. The cells incorporate selenium into protein to form selenoproteins, which are powerful antioxidants. These antioxidants contain properties that help prevent cellular damage incurred during the course of your body's normal metabolic processes. This damage can contribute to the development of dangerous diseases such as cancer. Evidence suggests that high sources of selenium, such as Brazil nuts, a large edible nut from South America, can protect against breast cancer.
History of Research
The relationship between selenium and breast cancer goes back to the 1960s, when epidemiological surveys suggested an inverse relationship between the incidence of breast cancer and the selenium content of the soil. Plants grown in the soils of the Pacific Northwest, the upper Midwest and the Northeast of the United States did not contain enough selenium at the time to prevent deficiencies. Later, a 1980 study published in the "Journal of Surgical Oncology" found that the addition of selenium in the diet decreased the rate of mammary tumors.
Later Studies
A more recent study from a 2006 issue of the "British Journal of Cancer" further illuminated the role selenium plays in the incidence of the disease. The researchers found that cancer patients had lower selenium concentrations in the blood compared to healthy patients but higher concentrations in the cancerous breast tissue, presumably reflecting some sort of defense mechanism against the carcinogenic process. They also found no correlation between selenium concentrations and the stage of the disease.
Brazil Nuts
Brazil nuts are the richest source of selenium in the diet. A single ounce contains as much as 544 mcg of selenium. The recommended dietary allowance for adults 19 years and older is only 55 mcg --- though pregnant and lactating women need 60 and 70 mcg, respectively. Brazil nuts thus represent 780 percent of the normal daily value. No other source of food contains more than 100 percent. The selenium within Brazil nuts and other foods appears to interact with an enzyme --- a special protein that facilitates chemical reactions --- to guard against the disease.
Considerations
There is no official recommendation for the amount of selenium in your diet that can reduce the rate of breast cancer. However, previous studies have used between 200 and 400 mcg of selenium a day to reduce the rate of general cancer mortality. The maximum tolerable intake is 800 mcg per day, but for safety reasons the suggestion is only about 400 mcg. Though Brazil nuts are an easy way to ensure high selenium intake without crowding out other nutrients, eat them only occasionally. Combined with other foods, Brazil nuts can result in too much selenium. The toxic effects of excessive selenium include hair loss, fatigue, immune deficiencies and brittle fingernails.
References
- Office of Dietary Supplements: Selenium
- Oregon State University Linus Pauling Institute; Selenium and Cancer: New Views; P.D. Whanger; November 1997
- "Journal of Surgical Oncology"; The Relationship of Dietary Selenium and Breast Cancer; K.P. McConnell, et al.; 1980
- "British Journal of Cancer"; Selenium in Serum and Neoplastic Tissue in Breast Cancer: Correlation with CEA; K. Charalabopoulos, et al.; August 2006
- "Daily Mail": Brazil Nuts Hold Cancer Hope
- "Journal of Trace Elements and Electrolytes in Health and Disease"; Further Observations on the Human Maximum Safe Dietary Selenium Intake in a Seleniferous Area of China; G. Yang and R. Zhou; December 1994
