~ Study Finds Selenium May Reduce Colorectal Cancer, Particularly in Smokers

A study conducted at a number of university medical centers, coordinated by the National Cancer Institute (NCI) and published in the Cancer Epidemiology, Biomarkers and Prevention (15, 2:315-20, 2006) investigated the potential interaction of smoking and serum selenium levels in advanced colorectal cancer. They found that higher serum levels of selenium may reduce the risk of advanced colorectal cancer, particularly in recent smokers.

Researchers studied the association between serum selenium and advanced colorectal adenoma in 758 cases and 767 sex- and race-matched controls, randomly selected from the Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial. Cases had at least one verified advanced adenoma of the distal colon, while controls had a negative sigmoidoscopy. While there was a significant inverse association between serum selenium and advanced colorectal adenoma among recent smokers, there was no relationship between serum selenium and adenoma risk in nonsmokers and former smokers who quit smoking more than 10 years before. The study concluded selenium may reduce the risk of developing advanced colorectal adenoma, particularly in the high-risk group of recent smokers.

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, natural by-products of 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.

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. In the U.S. commercial food distribution helps prevent people living in low-selenium geographic areas from suffering from low selenium intake. Soils in some parts of China and Russia have very low amounts of selenium and deficiency is reported there because most food in those areas is grown and eaten locally.

In the U.S., most cases of selenium deficiency are associated with severe gastrointestinal problems, such as Crohn's disease, or with surgical removal of part of the stomach. People with acute severe illness who develop inflammation and widespread infection often have decreased levels of selenium in their blood. Excessively high blood levels of selenium can result in a condition called selenosis. Symptoms of selenosis can include gastrointestinal upsets, hair loss, white blotchy nails, garlic breath odor, fatigue, irritability, and mild nerve damage.

Observational studies indicate that death from cancer, including lung, colorectal, and prostate cancers, is lower among people with higher blood levels or intake of selenium. In addition, the incidence of non-melanoma skin cancer is significantly higher in individuals with low blood levels of selenium. Research suggests that selenium affects cancer risk in two ways. As an anti-oxidant, selenium can help protect the body from damaging effects of free radicals. Selenium may also prevent or slow tumor growth.

Certain breakdown products of selenium are believed to prevent tumor growth by enhancing immune cell activity and suppressing development of blood vessels to the tumor. Individuals with rheumatoid arthritis may have reduced selenium blood levels. HIV/AIDS malabsorption can deplete levels of many nutrients, including selenium. Selenium deficiency is associated with decreased immune cell counts, increased disease progression, and high risk of death in the HIV/AIDS population.


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