~ 020108 Zinc May Protect Against Cadmium-Induced Rises in PSA

A report published in the February 15, 2008 issue of The Prostate revealed the discovery of University of Rochester researchers that zinc may have a protective effect against injury to the prostate induced by cadmium. Cadmium is a non-essential heavy metal that occurs in a number of environmental sources, including phosphate fertilizers and the food crops they are used on, industrial byproducts, smelter emissions, and cigarette smoke. Although epidemiological findings have been inconclusive, studies have shown that cadmium can induce prostate tumors in rats, and the element has been found in greater concentrations in cancerous prostate tissue than in normal tissue.

For the current study, University of Rochester School of Medicine and Dentistry epidemiologist Edwin van Wijngaarden, PhD and colleagues utilized information from 442 male participants in the 2001-2002 National Health and Nutrition Examination Survey (NHANES) for whom urinary cadmium concentrations, dietary zinc intake levels, and prostate specific antigen levels were available. Prostate specific antigen (PSA) increases during prostate injury or inflammation, and may predict prostate cancer, although not with complete accuracy.

Although the researchers did not find an association between increased cadmium and elevated PSA among men whose zinc intake was above the median of 12.67 milligrams per day, an association was found in men whose zinc intake was low. In this group, those with above median urinary cadmium levels had PSA levels that were 22 percent greater than those of men with lower cadmium levels. In the low zinc group, an increase of 1 unit of measurement of urinary cadmium was associated with a 35 percent increase in PSA.

"Your health is based on the complex interplay of many factors," Dr Van Wijngaarden explained. "Environmental exposures play out differently in people. It's important to identify those subpopulations that may be more sensitive to toxicities."

Cadmium's mechanism in the development of prostate cancer is likely to involve genotoxic effects, such as those resulting in reduced DNA repair and greater activation of genes associated with cell proliferation. Zinc stimulates the availability of proteins called metallothioneins which increase cadmium binding, resulting in its removal from circulation and a reduction of its adverse effects.

"Our findings appear to suggest a protective effect of zinc intake on cadmium-induced prostatic injury, which may provide further rationale for investigating the impact of these factors individually and jointly in the etiology of prostate cancer," the authors conclude.

Related Health Concern: Prostate Cancer

Measures to prevent prostate cancer (PC) must be a routine part of the counsel that general practitioners and internists give their patients. Selenium intake of at least 200 mcg a day should be a consideration in the prevention of PC. Low plasma selenium is associated with a four- to fivefold increased risk of PC. In addition, levels of plasma selenium also decrease with age, resulting in middle-aged to older men being at a higher risk for low selenium levels.

A large-scale study of almost 11,000 men in Maryland showed that the protective effects of high selenium levels, and similarly that of the alpha-tocopherol isomer of vitamin E, were only observed when the concentrations of the gamma tocopherol isomer of vitamin E were also high. In this study, the risk of PC declined with increasing concentrations of alpha-tocopherol, with the highest concentration associated with a 68% PC risk reduction. For gamma-tocopherol, men with levels in the highest fifth of the distribution had a fivefold greater reduction in the risk of developing PC than men in the lowest fifth (p = .002). The observed interaction between alpha-tocopherol, gamma-tocopherol, and selenium suggested that combined alpha- and gamma-tocopherol supplements, used in conjunction with selenium, should be considered in future PC prevention trials.

A report by Chan et al. (1999) showed significant benefit only to smokers or those recently quitting smoking in a study involving 47,780 U.S. male health professionals who received at least 100 IU of supplemental alpha-tocopherol. In this population, the risk of metastatic or fatal PC was reduced 56%. In the nonsmoking population, there were no beneficial findings of statistical significance.

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