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.
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