By comparison, the study found that selenium present in certain foods and supplements -- appeared to have little or no effect on non-smokers or current smokers. A possible explanation, the scientists suggest, is the element's reputed anti-oxidant activity.
"The lack of effect of selenium status among non-smokers is consistent with this hypothesis, since those who never smoked have not been exposed to smoking induced oxidative stress," said Maurice P.A. Zeegers, an assistant professor of epidemiology at Maastricht University in the Netherlands, and the study's lead author.
Also participating in the study, titled "Prediagnostic Toenail Selenium and Risk of Bladder Cancer," are Alexandra Goldbohm, with the Department of Nutritional Epidemiology at TNO Nutrition and Food Research, Zeist, the Netherlands; Peter Bode, with the Interfaculty Reactor Institute, Delft University of Technology; and Peit van den Brandt, also with the Department of Epidemiology, Maastricht Univerity, in Maastricht.
Bladder cancer is the most common cancer of the urinary tract and is the seventh most common cancer among men, accounting for about 200,000 new cases per year worldwide. Over the last four decades, many epidemiological studies and several reviews have suggested that bladder cancer is linked to environmental factors, including cigarette smoking, diet, fluid consumption, shistosomal infections and exposures to industrial chemicals.
Past research has suggested that diets rich in selenium result in lower incidences of cancer, particularly lung, colorectal and prostate cancers.