What is selenium?
Selenium is a trace mineral that is essential to good health but required only in small amounts. Selenium is incorporated into proteins to make selenoproteins, which are important antioxidant enzymes. The antioxidant properties of selenoproteins help prevent cellular damage from free radicals. Free radicals are natural by-products of oxygen metabolism that may contribute to the development of chronic diseases such as cancer and heart disease. Other selenoproteins help regulate thyroid function and play a role in the immune system.
What foods provide selenium?
Plant foods are the major dietary sources of selenium in most countries throughout the world. The content of selenium in food depends on the selenium content of the soil where plants are grown or animals are raised. For example, researchers know that soils in the high plains of northern Nebraska and the Dakotas have very high levels of selenium. People living in those regions generally have the highest selenium intakes in the United States (U.S).In the U.S., food distribution patterns across the country help prevent people living in low-selenium geographic areas from having low dietary selenium intakes. Soils in some parts of China and Russia have very low amounts of selenium. Selenium deficiency is often reported in those regions because most food in those areas is grown and eaten locally.
Selenium deficiency can lead to Keshan disease, which is potentially fatal. Selenium deficiency also contributes (along with iodine deficiency) to Kashin-Beck disease. The primary symptom of Keshan disease is myocardial necrosis, leading to weakening of the heart. Kashin-Beck disease results in atrophy, degeneration and necrosis of cartilage tissue. Keshan disease also makes the body more susceptible to illness caused by other nutritional, biochemical, or infectious diseases. These diseases are most common in certain parts of China where the soil is extremely deficient in selenium. Studies in Jiangsu Province of China have indicated a reduction in the prevalence of these diseases by taking selenium supplements.
Several studies have suggested a link between cancer and selenium deficiency. A study conducted on the effect of selenium supplementation on the recurrence of skin cancers did not demonstrate a reduced rate of recurrence of skin cancers, but did show a significantly reduced occurrence of total cancers. Dietary selenium prevents chemically induced carcinogenesis in many rodent studies. In these studies, organic seleno-compounds are more potent and less toxic than selenium salts (e.g., selenocyanates, selenomethionine, selenium-rich Brazil nuts, or selenium-enriched garlic or broccoli). Selenium may help prevent cancer by acting as an antioxidant or by enhancing immune activity. Not all studies agree on the cancer-fighting effects of selenium. One of the studies showed that in just 72 hours, the efficacy of treatment using chemotherapeutic drugs, such as Taxol and Adriamycin, with selenium yeast is significantly higher than the treatment using the drugs alone. The finding was shown in various cancer cells (breast, lung, small intestine, and colon, liver).
Some research has indicated a geographical link between regions of selenium deficient soils and peak incidences of HIV/AIDS infection. For example, much of sub-Saharan Africa is low in selenium. However, Senegal is not, and also has a significantly lower level of AIDS infection than the rest of the continent. AIDS appears to involve a slow and progressive decline in levels of selenium in the body. Whether this decline in selenium levels is a direct result of the replication of HIVor related more generally to the overall malabsorption of nutrients by AIDS patients remains debated.
Age Males and Females Pregnancy Lactation
(years) (μg/day) (μg/day) (μg/day)
1-3 y 20 N/A N/A
4-8 y 30 N/A N/A
9-13 y 40 N/A N/A
14-18 y 55 60 70
19 y + 55 60 70[/code]