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 Therapies manual are cited directly from the medical literature, and are intended to help in the objective evaluation of alternative/ complementary therapies.
Summary
There is insufficient evidence that zinc is effective in treating or preventing cancer in humans. High doses of zinc may have toxic side effects.
"This trace element... should never be used routinely by itself." (Diamond)
Description/ Source/ Components
"Zinc is an essential co-factor in a variety of cellular processes including DNA synthesis, behavioral responses, reproduction, bone formation, growth and wound healing." (Barceloux)
"Zinc is a component of insulin and it plays a major role in the efficiency of most of the functions of your body." (Ontario)
"Zinc is necessary for the free-radical quenching activity of superoxide dismutase (SOD), a powerful antioxidant enzyme which breaks down the free-radical superoxide to form hydrogen peroxide." (Diamond)
"Zinc is also required for the proper function of T-lymphocytes." (Boik)
"Natural sources include lean beef, egg yolks, fish, lamb, milk, oysters, pork, sesame and sunflower seeds, soybeans, turkey, wheat bran and germ, and whole-grain products." (Marti)
"The recommended daily allowance for adults is 15mg [milligrams] zinc." (Barceloux)
Proponent/ Advocate Claims - Use in Preventing Cancer
"Supporters report that high-dose zinc injections decrease the chance of getting cancer at the site of injection." (Ontario)
"Zinc might aid in the prevention and treatment of cancer. The effect of zinc on the immune system strengthens the body's defense against abnormal cell growth associated with cancer development. This essential trace mineral is also important in normal cell growth and development, which would aid in the prevention of any disease associated with abnormal cell growth." (Somer)
Professional Evaluation/ Critique - Use in Preventing Cancer
"Rogers and co-authors also explored the association between zinc and cancer of the mouth and found no significant relationship between any of their measures of zinc (diet, supplement, content level of zinc in finger/toe nails) and such cancers. (Rogers)" (World Cancer Research Fund)
An epidemiological study was done by Blot and colleagues "to determine if dietary supplementation with specific vitamins and minerals can lower mortality from or incidence of cancer as well as mortality from other disease in Linxian, China."... "Mortality and cancer incidence during March 1986 - May 1991 were ascertained for 29,584 adults who received daily vitamin and mineral supplementation throughout this period." The results of the study found that "no significant effects on mortality rates from all causes were found for supplementation with retinol and zinc..." (Blot)
"A randomized double-blind intervention was done in Huixian, People's Republic of China, a population with a high incidence of esophageal cancer. The aim of the trial was to determine whether a once-a-week treatment with retinol (15mg [milligrams] or 50,000 IU), riboflavin (200mg [milligrams]), and zinc (50mg [milligrams]) could result, after 1 year, in a lower prevalence of precancerous lesions of the esophagus in the group receiving the active treatment as compared with the prevalence in the group receiving a placebo. The results of the trial,... indicated that the treatment had no effect on the prevalence of precancerous lesions of the esophagus." (Munoz)
A study done by Bespalov and colleagues "was concerned with the influence of prolonged treatment with riboflavin, molybdenum, selenium and zinc on the induction of tumors of the esophagus and forestomach ...in rats." Once hyperplasia and dysplasia became evident in the mucous membrane of the esophagus and forestomach, zinc was given to the rats via their drinking water. The results showed that "zinc did not affect the carcinogenesis in the organs discussed." (Bespalov)
"The National Cancer Institute reports that the action of zinc is complex and that any possible benefit would depend on the dose, the route and the target site." (Ontario)
"...zinc has potential antioxidant effects, but its role in disease is unclear. (Strain) Zinc-deficient rats have an increase in single-strand DNA breaks in the liver and zinc leukocyte or plasma levels have been found to be low in cancer patients, but there is little evidence of a zinc deficiency in these patients." (Spencer)
"The effects of zinc on the initiation and progression of cancer are not well established, although the negative effects of zinc deficiency on the immune system are clear. (Linder)" (Boik)
Proponent/ Advocate Claims - Use in Treating Cancer
A paper by Mei and colleagues suggests that some aspects of immune function can be enhanced by treatment with zinc. The authors states that it would be "reasonable to expect that zinc... is instrumental in restoring failing immunocompetence of cancer patients." (Mei)
Professional Evaluation/ Critique - Use in Treating Cancer
"The effect of different levels of Zn intake on survival was studied in 6 groups of 4-week-old mice inoculated with tumor cells." Results showed that "excess Zn intake significantly prolonged the mean survival time when given at T11 [11 days after the mice were inoculated with tumor cells]. However, excess Zn intake at T0 [the time at which mice were inoculated with tumor cells] produced no significant effect on survival..." (Song)
Toxicity/ Risks
"Some believe that a high zinc intake may contribute to colon cancer and accelerate the growth of prostate cancer." (Ontario)
"Rats having received drinking water enriched with zinc developed significantly more pulmonal metastases after an intra venous injection of [cells of an induced sarcoma] than those receiving normal drinking water. Zinc ions seem to promote the emigration, implantation and outgrowth of circulating tumour cells." (Rath)
"Excessive amounts of zinc may cause iron and copper losses resulting in nausea, vomiting and diarrhea." (Ontario)
"Zinc in doses greater than 150mg [milligrams] might interfere with normal immune function, thus reducing the body's defense against disease. Long-term ingestion of 80 to 150 mg [milligrams] of zinc might lower HDL-cholesterol and, thus, increase risk for heart disease." (Somer)
"...ingesting extreme amounts of zinc daily can impair immune function and cause nausea, headaches, vomiting, dehydration, stomach-aches, poor muscle coordination, fatigue, and possibly kidney failure." (Time Life)
"Zinc compounds can produce irritation and corrosion of the gastrointestinal tract, along with acute renal tubular necrosis and interstitial nephritis [disease of the interstitial tissue of the kidney]." (Barceloux)
Kroll also includes Alzheimer's disease on a list of toxic effects resulting from megadoses of zinc. (Kroll)
A randomized, double-blind trial was done to measure the effects of zinc supplementation on catch-up growth in malnourished children between the ages of 6 months to 3 years. The study concluded that the use of high-dose zinc supplementation regimens "could contribute to increased mortality in severely malnourished children." (Doherty)
"Zinc intakes up to 100mg [milligrams] are safe if the diet is comprised of low bioavailable zinc, such as the zinc in foods of plant origin, and foods high in fiber and phytates." (Somer)
Costs
Zinc costs approximately 7$ for one hundred 50mg [milligrams] tablets. (Ontario)
References
Barceloux DG. Zinc. J Toxicol Clin Toxicol 1999;37:279-92.
Bespalov VG, et al. [The effect of riboflavin, molybdenum, selenium and zinc on the development of induced tumors of the esophagus and forestomach in rats.] Voprosy Onkologii 1990;36:559-63.
Blot JW, et al. Nutrition intervention trials in Linxian, China: supplementation with specific vitamin/mineral combinations, cancer incidence, and disease-specific mortality in the general population. J Natl Cancer Inst 1993;85:1483.
Boik J. Cancer and natural medicine: a textbook of basic science and clinical research. Oregon: Medical Press 1995:147.
Diamond WJ, et al. An alternative medicine definitive guide to cancer. Tiburon: Future Medicine Publishing, Inc., 1997:793.
Doherty CP, et al. Zinc and rehabilitation from severe protein-energy malnutrition: higher-dose regimens are associated with increased mortality. Am J Clin Nutr 1998;68:742-8.
Kroll D. Megadoses and Toxicity. Alternative and Complementary Therapies 1995 Jan/Feb: 111.
Linder MC. Nutritional Biochemistry and Metabolism, 2nd Ed. New York: Elsevier Science Publishing Co. Inc., 1991:499,512.
Marti JE. Alternative health medicine encyclopedia: the authoritative guide to holistic and nontraditional health practices. Toronto: Gale Research Inc., 1995:74.
Mei W, et al. Study of immune function of cancer patients influenced by supplemental zinc or selenium-zinc combination. Biol Trace Elem Res 1991;28:9-11.
Munoz N, et al. Effect of riboflavin, retinol, and zinc on micronuclei of buccal mucosa and of esophagus: a randomized double-blind intervention study in China. J Natl Cancer Inst 1987;79:687-91.
Ontario Breast Cancer Information Exchange Project. Guide to unconventional cancer therapies. 1st ed. Toronto: Ontario Breast Cancer Information Exchange Project, 1994:148.
Rath FW, et al. The influence of zinc administration on the development of experimental lung metastases after an injection of tumour cells into the tail vein of rats. Exp Pathol 1991;41:215-17.
Rogers MA, et al. A case-control study of element levels and cancer of the upper aerodigestive tract. Cancer Epidemiol Biomarkers Prev 1993;2:305-312.
Somer E and Health Media of America. Essential guide to vitamins and minerals. USA: Harper Perennial, 1995:32-3,139,142.
Song MK, et al. Effect of different levels of dietary zinc on longevity of BALB/c mice inoculated with plasmacytoma MOPC 104E. J Natl Cancer Inst 1984;72:647-52.
Spencer JW, Jacobs JJ. Complementary/alternative medicine: an evidence based approach. Toronto: Mosby, 1999:136.
Strain J. Putative role of dietary trace element in coronary heart disease and cancer. Br J Biomed Sci 1994;51:241.
Time Life. The medical advisor: the complete guide to alternative & conventional treatments. Alexandria, Virginia: Time Life Inc., 1996:1041.
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;102.
Revised February 2000