Abstract
BACKGROUND: Despite the implementation of national iodine supplementation programs, structural thyroid diseases are still highly prevalent in most countries. Thus, the link between trace elements other than iodine, such as selenium, and thyroid diseases should be investigated. METHODS: In this case-control study, adult patients with newly diagnosed papillary thyroid carcinoma, benign thyroid nodules, and healthy euthyroid controls without nodules were recruited. Thyroid function tests and serum selenium levels were assessed and compared between groups. The One-way ANOVA test was used to assess the mean difference of numerical variables among the three studied groups (PTC, Benign nodule, and healthy control group). In addition, a post-hoc comparison was conducted based on Bonferroni correction for a pairwise comparison of these three groups. RESULTS: Data from 182 patients with papillary thyroid carcinoma (PTC), 185 patients with benign thyroid nodules, and 180 healthy individuals as a control group were analyzed. The mean serum selenium levels in the PTC, benign thyroid nodules, and control group were 94.9, 121.6, and 134.3 µg/l, respectively (P < 0.001). There was a significant relationship between the cancer stage and selenium level in the PTC group. Patients in higher stages of cancer had a lower mean of selenium (P < 0.001). In univariate logistic regression, TSH and selenium were significant variables for PTC compared with patients with benign thyroid nodules. Each unit increase in selenium reduces the chance of PTC by about 6%. CONCLUSION: The low levels of selenium were associated with PTC. Also, serum selenium levels were inversely correlated with the stage of thyroid cancer.