Are nitrates a significant risk factor in human cancer?

This article focuses on the relationship between exposure to nitrates in the environment and subsequent risk of human cancer. The question of whether or not nitrates represent a cancer hazard is one of the most important public health issues arising from research into N-nitroso compounds. The reason for concern results from the endogenous reduction of nitrate to nitrite and subsequent nitrosation of amines, amides and proteins to give rise to carcinogenic N-nitroso compounds. The human evidence relating nitrate exposure to cancer, especially gastric cancer, has been largely based on geographic correlation studies, a relatively weak form of epidemiological methodology. In sum, this evidence and that from a small number of individually based studies does not support the hypothesis of a straightforward cause and effect association between nitrate exposure and cancer risk. Because many other factors besides nitrate are involved in the endogenous formation of N-nitrosation compounds, it is possible that exposure to nitrate is not a rate-limiting factor in most circumstances. This makes the setting of regulatory standards for nitrate exposure from the environment a complex issue.