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Nitrate and N‐nitrosoproline excretion in two italian regions with contrasting rates of gastric cancer: The role of nitrate and other factors in endogenous nitrosation

Exposure to nitrate and propensity for endogenous nitrosation were examined in 80 healthy males, aged 25–40 years, residing in areas of Italy with long‐standing high (Florence) and low (Cagliari) rates of gastric cancer. Nitrate exposure was assessed by measurement of urinary nitrate excretion over 12 hr, and endogenous nitrosation was assessed using the N‐nitrosoproline test (NPRO‐test). Our hypothesis was whether the geographic variation in cancer rate correlated with nitrate exposure or nitrosating ability. Exposure to background sources of NPRO was significantly higher in the high‐risk subjects (p = 0.04) whereas no differences were found in exposure to nitrate or in urinary NPRO levels after L‐proline loading (test NPRO levels). The regional difference in test NPRO was almost completely accounted for by background NPRO exposure. Examination of individual rather than grouped data revealed that exposure to nitrate was a major factor in NPRO formation. No other factors studied (age, dietary‐questionnaire‐assessed intake of anti‐oxidant vitamins) had a significant effect. Geographical variation in gastric cancer risk did not, therefore, correlate with either nitrate exposure or propensity for endogenous nitrosation of L‐proline.