Urinary excretion of N-nitrosamino acids and nitrate by inhabitants in high- and low-risk areas for stomach cancer in northern Japan.

Three samples of 24-h urine were collected from each of 104 inhabitants of high-risk (Akita) and low-risk (Iwate) areas for stomach cancer in northern Japan, according to the following protocols: (i) when they were undosed, (ii) after ingestion of proline three times a day and (iii) after ingestion of proline together with vitamin C three times a day. These samples were analysed for N-nitrosamino acids, nitrate and chloride ion as indices of the exposure. The median values of N-nitrosoproline (NPRO) and N-nitroso-2-methylthiazolidine 4-carboxylic acid (NMTCA) excreted in the urine of undosed subjects were not different between the two areas; however, that of N-nitrosothiazolidine 4-carboxylic acid (NTCA) was significantly higher in subjects of the high-risk area. Salt intake, estimated from the level of chloride ion in the urine, did not differ in two areas. After intake of proline, the NPRO level increased significantly only in subjects of the high-risk area, but not in those of the low-risk area; intake of vitamin C inhibited this increase of NPRO and lowered the levels of other nitrosamino acids only in the high-risk subjects. In contrast, the urinary level of nitrate was higher in subjects of the low-risk area than in those of the high-risk area; nitrate levels were found to correlate well with the amounts of vegetables consumed.(ABSTRACT TRUNCATED AT 250 WORDS)