In view of the experimental evidence suggesting that the micronutrient selenium reduces prostate cancer risk, we investigated the association between the selenium level in fingernails, a measure of long-term selenium intake, and prostate cancer risk in a case -control study among 656 British men, conducted in 1989British men, conducted in -1992. Nail clippings were taken at the time of recruitment and selenium concentration, measured using neutron activation techniques, was successfully assayed for 300 case -control pairs and varied six-fold among the controls (0.59 p.p.m.; interquartile range, 0.50 -0.71 p.p.m.). Nail selenium concentration was not significantly associated with prostate cancer risk: men in the highest quartile of nail selenium had a slightly increased risk compared with men in the lowest quartile (OR 1.24, 95 CI, 0.73 -2.10); for advanced prostate cancer, men in the highest quartile had a slightly reduced risk compared with men in the lowest quartile (OR 0.78, 95% CI, Selenium is an essential trace element found largely in grains, fish and meat products and has been shown to have antioxidant and other potentially anticarcinogenic properties (Combs and Gray, 1998). Experimental evidence indicates that selenium supplementation can reduce the incidence of viral and chemically induced tumours in animals (Vernie, 1984), including prostate cancer cell lines (Menter et al, 2000).The selenium content in foods varies widely between regions (Levander, 1987) because it is largely determined by the amount of selenium in the soil. Ecological data suggest that regional cancer mortality rates in the United States are inversely correlated with the selenium concentration in plants (Clark et al, 1991), and a randomised controlled trial among skin cancer patients found selenium supplementation of 200 mg day À1 to be associated with a significant 63% reduction in prostate cancer incidence (Clark et al, 1996;Duffield-Lillico et al, 2002). However, little is known about the relationship between the selenium status and prostate cancer risk in the general population.The aim of this study is to investigate the association between nail selenium concentration, a marker of long-term intake, and prostate cancer risk. A subsidiary aim is to examine whether factors that may influence selenium status, such as smoking (Hunter et al, 1990), vitamin E intake (Diplock, 1978) or the aggressiveness of disease at the time of recruitment (Yoshizawa et al, 1998;Goodman et al, 2001) modify the association between selenium concentration and prostate cancer risk.
SUBJECTS AND METHODSA population-based case -control study of the association between diet and prostate cancer was established in Britain, between 1989 and 1992, and included 328 men with incident prostate cancer and 328 population-based controls (Key et al, 1997). The study was restricted to white men under the age of 75 years who could speak English and who were well enough to complete a diet interview and give a reasonable history. Identification of cases was by searching a...