PROSPECTIVE-STUDY OF TOENAIL SELENIUM LEVELS AND CANCER AMONG WOMEN

Background: Inverse associations between selenium status and cancer ri sk have been observed in animal studies, ecologic studies, and some ca se-control and prospective studies, Whereas results of some prospectiv e studies have suggested an overall inverse relationship between selen ium levels and cancer, other prospective studies have failed to confir m this finding, Prospective data on women are particularly limited bec ause fewer women than men have been studied prospectively, Purpose: Th e aim of this study was to prospectively examine the relationship betw een selenium levels in toenails (previously shown to reflect selenium intake) and incidence of cancer among women, Methods: The Nurses' Heal th Study cohort began in 1976 with 121 700 female nurses aged 30-55 ye ars living in 11 U.S. states, In 1982, we requested toenail clippings from the members of the cohort, and 62 641 participants with no histor y of cancer returned these clippings, During 41 months of follow-up, 5 03 cases of cancer other than breast cancer (results previously report ed) or nonmelanoma skin cancer were analyzed, For each case patient, a control subject was chosen from women who remained free of diagnosed cancer, matched by age and by date of nail return, Results: No inverse association was observed between selenium levels in toenails and canc er risk, The age- and smoking-adjusted relative risk (RR), comparing t he highest with the lowest quintile of toenail selenium level, was 1.4 4 (95% confidence interval [CI] = 0.97-2.13), and the trend across qui ntiles was marginally significant (two-sided P = .06), Comparing the h ighest with the lowest decile, the RR (age- and smoking-adjusted) was 1.77 (95% CI = 1.04-3.02), When these data were combined with the data from 434 breast cancer case patients and their matched control subjec ts identified in parallel from this same cohort, the RR comparing the highest with the lowest quintile was 1.24 (95 % CI = 0.93-1.65), Toena il selenium level was not inversely associated with cancer at any majo r site, including uterine cancer, colorectal cancer, melanoma, ovarian cancer, or lung cancer (after adjusting for smoking); in fact, nonsig nificant positive associations were observed at several sites, Conclus ions: Toenail selenium levels were not inversely associated with cance r risk in this study, Implications: These data, in conjunction with pr evious findings of no association between toenail selenium status and breast cancer risk, strongly suggest that higher selenium intake withi n the range consumed by most U.S. women (as reflected by toenail selen ium levels) is not protective against overall cancer incidence in wome n.