Association between selenium level and bladder cancer; Systematic review and meta-analysis.

Bladder cancer is one of the common cancers in men. The different studies have shown different results on the effects of selenium on the risk of bladder cancer. The aim of this study was to determine the association between the selenium in serum, Toenail and supplements on the one hand and the risk of bladder cancer on the other. Doing a systematic review and meta-analysis of 9 studies (4 studies on the selenium level in the toenail, 2 studies in serum and 3 studies in supplements), therefore, it was tried to achieve some exact results of the association between selenium and the bladder cancer risk. The results showed there is no publication error in the observational studies (Begger's test = -0.71; 95% CI (-4, 2.66).In the subgroups of selenium supplement, serum and Toenail, the heterogeneity was I2 = 0% (P value = 0.81), I2 = 0% (P value = 0.35) and I2 = 1.47% (P value = 0.38) and overall I2 =63%(P value = 0.005), respectively.The risk ratio in the studies of selenium supplements, serum and Toenail was FEM = 1.02 (P value = 0.8), FEM = 0.3 (P value<0.001) and FEM = 0.85 (P value = 0.1) and in general FEM = 0.83 (P value = 0.01) respectively. The increase of selenium in supplements does not any effect on the increase or decrease of the bladder cancer (non-significant). The increase of selenium in serum and toenail reduces (significantly) the risk of bladder cancer in first case and (non-significantly) in second case. In general, the results of this study supported the lowering effect of selenium especially in serum on the risk of bladder cancer.