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The role of your cancer health professional is to create an environment of openness and trust, and to help in making informed decisions about alternative/complementary therapies. Collaboration will improve the safe integration of all therapies during your experience with cancer. The "Summary" and "Professional Evaluation / Critique" sections of this Unconventional manual are cited directly from the medical literature, and are intended to help in the objective evaluation of alternative/complementary therapies.
Summary
"Several lines of scientific inquiry suggest that an increased risk of cancer occurs as a result of low concentrations of selenium in the diet; however, insufficient evidence exists at the present time to recommend the use of selenium supplements for the prevention of cancer." (Barceloux)
There is insufficient evidence that selenium is effective as a treatment for cancer in humans.
Description / Source / Components
"Selenium is a key component of a number of functional selenoproteins required for normal health. The best known of these are the antioxidant glutathione peroxidase enzymes, which remove hydrogen peroxide and damaging lipid and phospholipid hydroperoxides generated in vivo by free radicals and other oxygen derived species." (Rayman)
Natural sources of selenium include brewer's yeast, organ meats, egg yolks, dairy products, fish and shellfish and whole grains. (Ontario)
"Dietary intakes show a large geographical variation, mainly because of differences in selenium bioavailability, which is generally low in Europe [and areas of China]." (Rayman)
History
"About 30 years ago, Shamberger and Frost suggested that regional cancer mortality rates in the USA correlated inversely with selenium exposure, as reflected by concentrations in plants. In subsequent decades, the association between blood concentration of selenium and risk of various cancers has been explored in several epidemiological studies." (Giovannucci)
Proponent / Advocate Claims - Use in Preventing Cancer
"Selenium is an antioxidant which is believed by proponents to protect you from free radical attack. Free radicals are believed to lead to cancer. ... Advocates argue that selenium helps reduce the incidence of breast, lung, colorectal and skin cancers." (Ontario)
"Selenium compounds have been found to inhibit tumorigenesis in a variety of animal models, and recent studies indicate that supplemental Se [selenium] in human diets may reduce cancer risk." (Combs)
"...research indicates that optimal selenium levels in the diet and body offer significant anticancer effects." (Murray)
"Gupta and co-workers studied plasma selenium levels in cancer patients and found that mean plasma selenium levels fell with increasing extent of disease and that patients with recurrent cancers had lower levels than those without recurrence. Gupta and colleagues believed that the low level is a causative factor in the cancer. (Gupta)" (Spencer)
Yoshizawa and colleagues "investigated the association between risk of prostate cancer and prediagnostic level of selenium in toenails, a measure of long-term selenium intake." They concluded that their results "support earlier findings that higher selenium intakes may reduce the risk of prostate cancer. Further prospective studies and randomized trials of this relationship should be conducted." (Yoshizawa)
The results of a study that measured serum selenium levels and T lymphocyte subsets in patients with large bowel cancer indicate that "Se [selenium] can promote cell-mediated immunity in humans." The authors concluded that "this indicates that there may be a close relationship between low Se level and the carcinogenesis of the colon and rectum." (Yu 1996)
Professional Evaluation / Critique - Use in Preventing Cancer
"...there is still an absence of clinical studies in humans." (Spencer)
"Several lines of scientific inquiry suggest that an increased risk of cancer occurs as a result of low concentrations of selenium in the diet; however, insufficient evidence exists at the present time to recommend the use of selenium supplements for the prevention of cancer." (Barceloux)
"One NCI study reported a 16% decrease in incidence of gastric cancer, a 4% reduction in esophageal cancer, and an overall 20% reduction in other cancers in a large group of Chinese adults taking vitamin E, beta-carotene, and selenium as compared with a control group. (Long) Because the study did not compare single variables, it is impossible to say what the role of each of the three additives is." (Spencer)
"Earlier studies on selenium yielded inconsistent results. Some found it protective against certain cancers, but not always against the same cancers, and usually only in regions of the world (notably parts of China) where people have extremely low blood levels of selenium. Other studies found no protective effect. And still others found that the mineral can increase the risk of some cancers." (Anonymous)
Clark and colleagues conducted a multicentre, double-blind, randomized, placebo-controlled cancer prevention trial "to determine whether a nutritional supplement of selenium will decrease the incidence of cancer." They concluded from the results of the study; "selenium treatment did not protect against development of basal or squamous cell carcinomas of the skin. However, results from secondary end-point analyses support the hypothesis that supplemental selenium may reduce the incidence of, and mortality from, carcinomas of several sites. These effects of selenium required confirmation in an independent trial of appropriate design before new public health recommendations regarding selenium supplementation can be made." (Clark)
With respect to the study done by Clark and colleagues [above], these comments have been made: "The subjects were a very special population. They all had had skin cancer, and they were chosen because they came from parts of the U.S. (mostly in the Southeast) where the soil has low selenium levels. They had blood levels far below the American average. It can't be assumed that the same effects would occur in the general population." (Anonymous)
With respect to the study done by Clark and colleagues, Colditz states that "it is premature to change individual behavior, to market specific selenium supplements, or to modify public health recommendations based on the results of this one randomized trial." (Colditz)
The World Cancer Research Fund summarizes the data regarding selenium as a preventive agent against cancer. The data suggests that "dietary selenium is possibly unrelated to the risk of colorectal cancer." ... "The evidence suggests that dietary selenium may decrease the risk of liver cancer, but is, as yet, insufficient." ... "The evidence suggests that high dietary selenium intake may decrease the risk of stomach and thyroid cancer, but is, as yet, insufficient." Evidence that dietary intake of selenium decreases the risk of bladder, breast, oesophageal, and pancreatic cancer is limited. "No judgement is possible." (World Cancer Research Fund)
"So where does this leave us with regard to selenium and prostate cancer? The accumulated evidence is limited and inconsistent, but it is extremely provocative." (Taylor)
Proponent / Advocate Claims - Use in Treating Cancer
Zhu and colleagues studied the biological effect of selenium on human glioma cell lines. "Selenium exhibited an antiproliferative effect on these cell lines... These findings demonstrate that selenium may induce, by apoptosis, cell death of human glioma cell lines..." (Zhu)
Professional Evaluation / Critique - Use in Treating Cancer
"While the potential for Se [selenium] to be useful in cancer chemotherapy would appear clear, many questions remain concerning the types of tumors that may be affected, the chemical forms of Se that may be effective, and the dose regimens that may be appropriate." (Garewal)
Toxicity / Risks
"Symptoms of selenium toxicity include hair, tooth and nail loss and dermatitis." (Ontario)
"The toxicity of most forms of selenium is low and the toxicity depends on the chemical form of selenium. The acute ingestion of selenious acid is almost invariably fatal, preceded by stupor, hypotension, and respiratory depression. Chronic selenium poisoning has been reported in China where changes in the hair and nails resulted from excessive environmental exposures to selenium. Garlic odor on the breath is an indication of excessive selenium exposure as a result of the expiration of dimethyl selenide. The US National Toxicology Program lists selenium sulfide as an animal carcinogen, but there is no evidence that other selenium compounds are carcinogens." (Barceloux)
"Selenium toxicity can occur from either acute or chronic exposure. ... Individuals often develop characteristic symptoms including a garlic or sour breath odor, nausea, vomiting, abdominal pain, restlessness, hypersalivation, and muscle spasms. Death is preceded by refractory hypotension from direct myocardial depression and peripheral vasodilation. ... Heavily exposed individuals may demonstrate gastroenteritis [inflammation of the lining of the stomach and intestines], hair and nail changes, and neurologic manifestations including acroparesthesias [a disease marked by tingling, numbness, and stiffness in the extremities], weakness, convulsions, and decreased cognitive function." (Strukle)
"The optimal size of dose for supplementation is controversial with respect to both efficacy and safety. In China, selenosis was observed in some individuals with a sustained intake of at least 750 micrograms/day [0.75 milligrams/day]but was not observed among others with intakes exceeding 1 mg. [1 milligram/day]... A large-scale Se human intervention trial in the United States suggests no harm due to long-term Se intake of more than 200 micrograms/day [0.2 milligrams/day]." (Patterson)
Hofbauer and colleagues report "a patient in whom, along with standard therapy, administration of large intravenous doses of selenite for sepsis secondary to pneumonia resulted in development of marked hypothyroidism. In addition, severe iodine deficiency was noted, and supplementation with iodine led to normalization of thyroid function." (Hofbauer)
Costs
Selenium costs approximately 7$ for one hundred 100mcg tablets. [Note: the original reference quotes "100 mg" (milligrams), but this has been verified by the BC Cancer Agency as being incorrect] (Ontario)
References
Anonymous. The selenium shocker. University of California at Berkeley Wellness Letter 1997;13:8-9.
Barceloux DG. Selenium. J Toxicol Clin Toxicol 1999;37:145-72.
Clark L, et al. Effects of selenium supplementation for cancer prevention on patients with carcinoma of the skin: a randomized controlled trial. JAMA 1996;276:1957.
Colditz GA. Selenium and cancer prevention: promising results indicate further trials required. JAMA 1996;276:1984-5.
Combs GF, Gray WP. Chemopreventive agents: selenium. Pharmacol Ther 1998;79:179-92.
Garewal HS. Antioxidants and disease prevention. New York: CRC Press, 1997:106.
Giovannucci E. Selenium and risk of prostate cancer. Lancet 1998;352:755.
Gupta S, et al. Plasma selenium levels in cancer patients. Indian J Cancer 1994;31:192.
Hofbauer LC, et al. Selenium, induced thyroid dysfunction. Postgrad Med J 1997;73:103-4.
Long K, Long R. Diet and development of cancer. Nurse Pract Forum 1995;6:183.
Murray MT. Encyclopedia of nutritional supplements: the essential guide for improving your health naturally. Prima Health, 1996:224.
Ontario Breast Cancer Information Exchange Project. Guide to unconventional cancer therapies. 1st ed. Toronto: Ontario Breast Cancer Information Exchange Project, 1994:144. [Note: the original "Cost" reference quotes "100 mg" (milligrams) as the tablet strength, but this has been verified by the BC Cancer Agency as being incorrect]
Patterson BH, Levander OA. Naturally occurring selenium compounds in cancer chemoprevention trials: a workshop summary. Cancer Epidemiol Biomarkers Prev 1997;6:63-9.
Rayman MP. Dietary selenium: time to act. BMJ 1997;314:387.
Spencer JW, Jacobs JJ. Complementary/alternative medicine: an evidence based approach. Toronto: Mosley, 1999:134,137.
Strukle E, et al. Selenium poisoning from a nutritional supplement. JAMA 1996;275:1087-8.
Taylor RP, Albanes D. Selenium, vitamin E, and prostate cancer - ready for prime time? J Natl Cancer Inst 1998;90:1184-5.
World Cancer Research Fund in Association with American Institute for Cancer Research. Food, nutrition and th-e prevention of cancer: a global perspective. World Cancer Research Fund/American Institute for Cancer Research, 1997;124,157,187,208,236,277,325,343.
Yoshizawa K, et al. Study of prediagnostic selenium level in toenails and the risk of advanced prostate cancer. J Natl Cancer Inst 1998;90:1221.
Yu B, et al. [The relationship between selenium and immunity in large bowel cancer]. Chung-Hua Wai Ko Tsa Chih 1996;34. [Abstract]
Zhu Z, et al. Apoptosis induced by selenium in human glioma cell lines. Biol Trace Elem Res 1996;54:123-34.
Revised February 2000
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