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Low Blood Selenium and Cancer

Jul 24, 2011 | By Maria Hopper
Low Blood Selenium and Cancer
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Selenium is a trace mineral, meaning that it is required in very small quantities for good health. Selenium is used by the thyroid gland and is important to the proper functioning of the immune system. It is involved in antioxidant defenses protecting the body from damaging free radicals. Laboratory experiments have indicated it may also inhibit tumor growth. Low blood selenium may increase susceptibility to cancer, although studies of this effect have shown inconsistent results.

Selenium Supplementation Research

The Nutritional Prevention of Cancer Trial run in the 1990s compared over 1,000 nonmelanoma skin cancer patients who received either 200 mcg of selenium from yeast or a placebo over a mean of 4.5 years. Although the study's main focus was recurrence of skin cancer, occurrences of other cancers in these patients were also analyzed. The study found no protective effect for selenium in recurrence of skin cancer. In fact, there was a slight increase in squamous cell carcinomas in the selenium-supplemented group. However, results reported in "Cancer Epidemiology, Biomarkers and Prevention" in July and November 2002 showed that patients who started off with the lowest serum selenium levels, which ranged from 42 to 106 ng/ml, saw reductions in prostate and lung cancer risk with supplementation. Patients who had the highest baseline selenium levels, at 122 to 220 ng/ml, appeared to increase their cancer risk slightly by taking supplements.

Lung Cancer Risk in a Low Selenium Population

A Finnish study indicated that very low blood selenium levels may make people more susceptible to lung cancer. In Finland, the soil is naturally low in selenium, which led to low selenium in the national diet. The government began fertilizing with selenium in 1984 to correct the problem. A study published in the "American Journal of Epidemiology" in November 1998 measured serum selenium levels in over 9,000 Finns from 1968 to 1976. Follow-up in 1991 revealed that those who previously had serum selenium levels of less than 46 ng/ml were more likely to get lung cancer.

Studies Show No Link Between Selenium and Cancer

Other large epidemiological studies have not found any protective effect for selenium with respect to cancer risk. Selenium was measured in toenail clippings, which indicates long-term dietary intake, in over 62,000 women in the Nurses' Health Study. Selenium was not found to protect from breast, uterine, colorectal, melanoma, ovarian or lung cancer, according to an April 1995 article in the "Journal of the National Cancer Institute." There was a statistically insignificant possibility of slightly higher rates of some cancers at the highest selenium levels. According to a very large study reported in "Cancer Epidemiology, Biomarkers and Prevention" in August 2010, in which retirees who were cancer-free took food-frequency questionnaires, there was no impact of selenium intake on lung cancer risk after seven years.

Selenium in Food

Selenium is taken up from the soil by plants. Areas with higher selenium content in soil will produce more selenium-rich crops. Since most areas of the United States have sufficient selenium in the soil and people consume crops from a variety of regions, selenium deficiency is rare here. Grains are a good source of selenium. Livestock diets are supplemented with selenium as necessary so that meats are good sources of the mineral. Fish, eggs and dairy products contain significant selenium. Brazil nuts are especially high in selenium and should only be eaten occasionally.

Intake Recommendations

The Food and Nutrition Board of the Institute of Medicine recommends that adults get 55 mcg of selenium per day. Under normal circumstances, this should be obtained from a balanced diet. People with severe gastrointestinal problems who do not absorb nutrients well may need supplements and should consult with their doctor. Supplements can be inorganic in the form of selenite or selenate, or they can be organic in the form of selenomethionine. Selenomethionine is found in food and in yeast-derived supplements and is thought to be better utilized by the body. The Food and Nutrition Board has set a tolerable upper limit of 400 mcg of selenium per day to avoid toxicity. Toxicity symptoms include nausea, nail changes, hair loss, diarrhea, fatigue and irritability.

References

Article reviewed by TimDog Last updated on: Jul 24, 2011

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