title: Is the inverse association between selenium and bladder cancer due to confounding by smoking?
abstract: Selenium has been linked to a reduced risk of bladder cancer in some studies. Smoking, a well-established risk factor for bladder cancer, has been associated with lower selenium levels in the body. We investigated the selenium-bladder cancer association in subjects from Maine, New Hampshire, and Vermont in the New England Bladder Cancer Case-Control Study. At interview (2001-2005), participants provided information on a variety of factors, including a comprehensive smoking history, and submitted toenail samples, from which we measured selenium levels. We estimated odds ratios and 95% confidence intervals among 1,058 cases and 1,271 controls using logistic regression. After controlling for smoking, we saw no evidence of an association between selenium levels and bladder cancer (for fourth quartile vs. first quartile, odds ratio (OR) = 0.98, 95% confidence interval (CI): 0.77, 1.25). When results were restricted to regular smokers, there appeared to be an inverse association (OR = 0.76, 95% CI: 0.58, 0.99); however, when pack-years of smoking were considered, this association was attenuated (OR = 0.91, 95% CI: 0.68, 1.20), indicating potential confounding by smoking. Despite some reports of an inverse association between selenium and bladder cancer overall, our results, combined with an in-depth evaluation of other studies, suggested that confounding from smoking intensity or duration could explain this association. Our study highlights the need to carefully evaluate the confounding association of smoking in the selenium-bladder cancer association.
authors.forename: Laura E
authors.initials: LE
authors.lastname: Beane Freeman
authors.forename: Margaret R
authors.initials: MR
authors.lastname: Karagas
authors.forename: Dalsu
authors.initials: D
authors.lastname: Baris
authors.forename: Molly
authors.initials: M
authors.lastname: Schwenn
authors.forename: Alison T
authors.initials: AT
authors.lastname: Johnson
authors.forename: Joanne S
authors.initials: JS
authors.lastname: Colt
authors.forename: Brian
authors.initials: B
authors.lastname: Jackson
authors.forename: G M Monawar
authors.initials: GM
authors.lastname: Hosain
authors.forename: Kenneth P
authors.initials: KP
authors.lastname: Cantor
authors.forename: Debra T
authors.initials: DT
authors.lastname: Silverman
mesh_terms: D000328:Adult; D000368:Aged; D016022:Case-Control Studies; D016001:Confidence Intervals; D015986:Confounding Factors, Epidemiologic; D005260:Female; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D009262:Nails / Q000737:chemistry*; D009511:New England; D016017:Odds Ratio; D065840:Protective Factors; D012307:Risk Factors; D012643:Selenium / Q000032:analysis* / Q000502:physiology; D012907:Smoking / Q000009:adverse effects* / Q000378:metabolism; D001749:Urinary Bladder Neoplasms / Q000737:chemistry* / Q000209:etiology / Q000517:prevention & control
chemical_list: D012643:Selenium
keywords: bladder cancer; case-control study; selenium; smoking