Selenium is an essential micro-nutrient whose best source is seafood given its gradual disappearance from intensively farmed soils. Selenium is toxic in extremely high doses but regarded as safe at normal supplement levels of 50-200 micrograms/day. A potent antioxidant, Selenium is an important co-factor for the body's natural antioxidant glutathione peroxidase system. Selenium in partnership with Vitamin E protects against cancer and prevents lipid peroxidation. Selenium is an effective detoxifier of heavy metals and boosts immune function against bacterial and viral infections.
The most important recent study on Selenium came from the University of Arizona where researchers were looking at the relationship of Selenium to specific skin cancers in 1,312 volunteers with an average age of 62 and a history of skin cancer. Each participant received either 200 micrograms of yeast-Selenium daily, or a matching placebo.
After the study had been in progress for 10 years, researchers found that, although incidence of non-melanoma skin cancer had not been influenced by the supplement, new cases of life-threatening cancers were 37% lower among those taking Selenium with highly significant reductions in the incidence of colorectal and prostate cancer. The probability was less than 1 in 1,000 that this beneficial effect occurred by chance. Possibly more significant, the study found that the total cancer death rate was 50% lower in the treated group, with mortality from lung cancer significantly and substantially reduced.
A second lesson from the study was that larger than previously used doses of Selenium, 200 mcg per day in the form of Selenium yeast, were extremely well-tolerated with no side effects or other evidence of toxicity, contrary to earlier reports and concerns that such high doses of Selenium would be toxic. Most Americans get less than 100 micrograms of Selenium a day without supplementation, as the trace mineral occurs naturally in food, but in reduced amounts secondary to gradual depletion from soils.
Selected References
Alaejos MS et al. Selenium and cancer: some nutritional aspects. Nutrition 16(5):376-83, 2000.
Backovic D et al. Environmental factors, health-related habits, and serum selenium levels in cancer patients and healthy controls. Biological Trace Element Research 67(2): 55-62, 1999.
Clark LC et al. Effects of selenium supplementation for cancer prevention in patients with carcinoma of the skin. A randomized controlled trial. Nutritional Prevention of Cancer Study Group. JAMA 276(24):1957-63, 1996.
Clark LC et al. Decreased incidence of prostate cancer with selenium supplementation: results of a double-blind cancer prevention trial. Br J Urol 81(5):730-4, 1998.
Clark LC et al. Plasma selenium concentration predicts the prevalence of colorectal adenomatous polyps. Cancer Epidemiol Biomarkers Prev 2(1):41-6, 1993.
Combs GF Jr et al. Reduction of cancer mortality and incidence by selenium supplementation. Med Klin 92 Suppl 3:42-5, 1997.
Ip C. Lessons from basic research in selenium and cancer prevention. J Nutr 128(11):1845-54, 1998.
Rayman MP. The importance of selenium to human health. Lancet 356(9225):233-41, 2000.