Selenium (as selenomethionine)
Selenium (pronounced /sɨˈliːniəm/ sə-LEE-nee-əm) is a chemical element with the atomic number 34, represented by the chemical symbol Se, an atomic mass of 78.96. It is a nonmetal, chemically related to sulfur and tellurium, and rarely occurs in its elemental state in nature.
Several studies have suggested a possible link between cancer and selenium deficiency. One study, known as the NPC, was conducted to test the effect of selenium supplementation on the recurrence of skin cancers on selenium-deficient men. It did not demonstrate a reduced rate of recurrence of skin cancers, but did show a reduced occurrence of total cancers, although without a statistically significant change in overall mortality. The preventative effect observed in the NPC was greatest in those with the lowest baseline selenium levels. In 2009 the 5.5 year SELECT study reported that selenium and vitamin E supplementation, both alone and together, did not significantly reduce the incidence of prostate cancer in 35,000 men who “generally were replete in selenium at baseline”. The SELECT trial found that vitamin E did not reduce prostate cancer as it had in the Alpha-Tocopherol, Beta Carotene (ATBC) study, but the ATBC had a large percentage of smokers while the SELECT trial did not. There was a slight trend toward more prostate cancer in the SELECT trial, but in the vitamin E only arm of the trial, where no selenium was given.
Dietary selenium prevents chemically induced carcinogenesis in many rodent studies. It has been proposed that 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 study of naturally occurring levels of selenium in over 60,000 participants did not show a significant correlation between those levels and cancer. The SU.VI.MAX study concluded that low-dose supplementation (with 120 mg of ascorbic acid, 30 mg of vitamin E, 6 mg of beta carotene, 100 µg of selenium, and 20 mg of zinc) resulted in a 30% reduction in the incidence of cancer and a 37% reduction in all-cause mortality in males, but did not get a significant result for females. However, there is evidence that selenium can help chemotherapy treatment by enhancing the efficacy of the treatment, reducing the toxicity of chemotherapeutic drugs, and preventing the body’s resistance to the drugs. Studies of cancer cells in vitro showed that chemotherapeutic drugs, such as Taxol and Adriamycin, were more toxic to strains of cancer cells grown in culture when selenium was added.
In March 2009, Vitamin E (400 IU) and selenium (200 micrograms) supplements were reported to affect gene expression and can act as a tumor suppressor. Eric Klein, MD from the Glickman Urological and Kidney Institute in Ohio said the new study “lend credence to the previous evidence that selenium and vitamin E might be active as cancer preventatives”. In an attempt to rationalize the differences between epidemiological and in vitro studies and randomized trials like SELECT, Klein said that randomized controlled trials “do not always validate what we believe biology indicates and that our model systems are imperfect measures of clinical outcomes in the real world”.
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 HIV or related more generally to the overall malabsorption of nutrients by AIDS patients remains debated.
Low selenium levels in AIDS patients have been directly correlated with decreased immune cell count and increased disease progression and risk of death. Selenium normally acts as an antioxidant, so low levels of it may increase oxidative stress on the immune system leading to more rapid decline of the immune system. Others have argued that T-cell associated genes encode selenoproteins similar to human glutathione peroxidase. Depleted selenium levels in turn lead to a decline in CD4 helper T-cells, further weakening the immune system.
Regardless of the cause of depleted selenium levels in AIDS patients, studies have shown that selenium deficiency does strongly correlate with the progression of the disease and the risk of death.
Some research has suggested that selenium supplementation, along with other nutrients, can help prevent the recurrence of tuberculosis.
When selenium (as selenomethionine – an amino acid containing selenium) is taken in small amounts, such as with the HRT ingested suspended gel heart health supplement (70 µg) there are health benefits without associated risks.
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