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How are nitrosamines formed?

N-nitroso-compounds, including nitrosamines and nitrosamides, are formed by a process called N-nitrosation. In the presence of nitrite, this process can take place in the human stomach. (Because nitrosamines are much more stable after food processing than nitrosamides, they are of greater potential concern.) Nitrite can be introduced into the stomach by consuming foods that contain it and from endogenous conversion of nitrate to nitrite. Nitrate can be derived from dietary sources or from the body's normal nitrogen metabolism.

Ascorbate, erythorbate, and tocopherol inhibit nitrosamine formation in the body resulting from dietary nitrite or nitrate exposure. This may be the reason why the intake of nitrate from vegetables is of little human health concern; they tend to be rich in antioxidants, such as vitamin C, that inhibit potential nitrosamine formation.

Of greatest concern is exposure to preformed nitrosamines, which mainly come from non-dietary sources. Tobacco products are the foremost source of preformed nitrosamines. Smoking directly exposes the body to these carcinogens.

Foods are minor contributors to overall exposure to preformed nitrosamines. The use of nitrite in bacon results in very low levels of nitrosamines, which at higher levels, have been shown to be carcinogenic in laboratory animals. However, with normal bacon consumption the concentrations are very low.

Beer, whiskey, and other malt-brewed alcoholic beverages have also been shown to contain very low levels of preformed nitrosamines. However, manufacturers have substantially reduced these substances in beverages and foods through processing modifications.