Recent studies on N-nitroso compounds as possible etiological factors in oesophageal cancer

Possible etiological factors involved in oesophageal cancer in various parts of the world and in certain provinces in Northern China are summarized. Evidence is accumulating that N-nitroso compounds and their precursors are involved in the disease in Northern China, as shown in a recent study: excretion of urinary N-nitrosamino acids by inhabitants living in a high- (Linxian) and in a low-risk area (Fanxian) for oesophageal cancer was compared. Linxian subjects excreted significantly more nitrate and nitrosamino acids (N-nitrosoproline, N-nitrosothiazolidine-4-carboxylic acid, N-nitrososarcosine) than those in Fanxian. When Linxian subjects were given 100 mg vitamin C three times a day (after each meal) together with proline, the level of urinary N-nitrosamino acids was reduced to that found in Fanxian. Thus, vitamin C, an efficient inhibitor of endogenous nitrosation, should now be examined in intervention trials in subjects in whom endogenous formation of N-nitroso compounds is elevated.