Lack of Association between Fingernail Selenium and Thyroid Cancer Risk: A Case-Control Study in French Polynesia

• Published in: Asian Pacific journal of cancer prevention : APJCP Vol. 15; no. 13; pp. 5187 - 5194
• Main Authors: Ren, Yan, Kitahara, Cari Meinhold, de Gonzalez, Amy Berrington, Clero, Enora, Brindel, Pauline, Maillard, Stephane, Cote, Suzanne, Dewailly, Eric, Rachedi, Frederique, Boissin, Jean-Louis, Sebbag, Joseph, Shan, Larrys, Bost-Bezeaud, Frederique, Petitdidier, Patrick, Xhaard, Constance, Rubino, Carole, de Vathaire, Florent
• Format: Journal Article
• Language: Korean
• Published: 2014
• Subjects: Thyroid cancer; selenium; fingernail; case-control study; diet
• ISSN: 1513-7368; 2476-762X

Background: Numerous studies have suggested that selenium deficiency may be associated with an increased risk for several types of cancer, but few have focused on thyroid cancer. Materials and Methods: We examined the association between post-diagnostic fingernail selenium levels and differentiated thyroid cancer risk in a French Polynesian matched case-control study. Conditional logistic regression models were used to estimate odds ratios and 95% confidence intervals. Results: The median selenium concentration among controls was $0.76{\mu}g/g$. Significantly, we found no association between fingernail selenium levels and thyroid cancer risk after conditioning on year of birth and sex and additionally adjusting for date of birth (highest versus lowest quartile: odds-ratio=1.12, 95% confidence interval: 0.66-1.90; p-trend=0.30). After additional adjustment for other covariates, this association remained non-significant (p-trend=0.60). When restricting the analysis to thyroid cancer of 10 mm or more, selenium in nails was non-significantly positively linked to thyroid cancer risk (p-trend=0.09). Although no significant interaction was evidenced between iodine in nails and selenium in nails effect (p=0.70), a non-significant (p-trend =0.10) positive association between selenium and thyroid cancer risk was seen in patients with less than 3 ppm of iodine in nails. The highest fingernail selenium concentration in French Polynesia was in the Marquises Islands ($M=0.87{\mu}g/g$) and in the Tuamotu-Gambier Archipelago ($M=0.86{\mu}g/g$). Conclusions: Our results do not support, among individuals with sufficient levels of selenium, that greater long-term exposure to selenium may reduce thyroid cancer risk. Because these findings are based on post-diagnostic measures, studies with prediagnostic selenium are needed for corroboration.