The biochemistry of nitrates, nitrites, nitrosamines and other potential carcinogens in human saliva.

Human whole saliva protects the oral environment in many different ways from invading pathogenic microorganisms. Human saliva is also capable of inactivating mutagenic and carcinogenic agents by various mechanisms. The peroxidation of these agents is likely to be one of the degrading reactions. However, under certain circumstances some potentially carcinogenic compounds, such as N-nitrosamines, may be generated in whole saliva or--even more likely--in the saliva-gastric juice mixture after swallowing. The formation of N-nitroso compounds requires relatively high intake of nitrate e.g. from vegetable juices. Nitrate is partly reduced to nitrite by oral bacterial enzymes. The nitrosation of various secondary amines is favoured by high salivary (or gastric) concentration of thiocyanate and by low pH. The endogenous generation of N-nitroso compounds may be causally related to the development of oral or gastric cancer.