Association between nitrate in drinking water and risk of bladder cancer; Systematic review and meta-analysis update to May 2016

Nitrate is a water-soluble compound which can endanger the health of human and other living creatures at high concentrations. Although bladder cancer caused by nitrates is biological plausibility, but the number of studies on the relationship between nitrate exposure and the risk of bladder cancer is limited. Therefore, in this study, it has been tried to reevaluate the relationship between nitrate exposure and the risk of bladder cancer through systematic review and meta-analysis. The databases of ISI, Pubmed,Scopus, Irandoc and SID were used to find the studies in Iran and the world. Generally, 6 studies including 1 ecological study, 3 case-control studies and 2 cohort studies were entered at the meta-analysis stage. At the stage of meta-analysis, the heterogeneity of the studies with high scores was I2=52%,P<0.001, so, Random effect model was used for them and the heterogeneity of the studies with low scores was I2=0%,P=0.53,so,Fixed effect model was used for them. For the studies with high scores, REM=0.93 (P value=0.22) and for studies with low scores, REM=1.77 (P value<0.001). In high quality studies, the risk of bladder cancer was reduced by 7% significantly and in low quality studies, it was reduced by 77% significantly. The relative mean risk of 6 studies was REM=1.03 (P value=0.58). The results of the systemic review and meta-analysis showed that the drinking-water nitrate has no effects on the increase or reduction in the risk of bladder cancer and performing further studies on this issue is needed