Epidemiology of stomach cancer in Chile--the role of nitrogen fertilizers.

Chile ranks second in the world regarding age-adjusted mortality rates from stomach cancer. Analysis of death rates along its 25 provinces for a 15-year period (1957-1971) shows a peculiar geographic pattern of high and low-risk areas. Three agricultural provinces (Maule, Linares and Nuble, located south of Santiago), population 460,000, show a median rate of 50 x 1 per 100,000. In contrast, both extremes of the country, distant some 3,000 miles from one another, carry less than one-half the risk. The three northerly provinces (Tarapacá, Antofagasta and Atacama), population 652,500, show a median rate of 21 6, whereas Aysén and Magallanes in the extreme south, population 161,600, share a figure of 22.8 per 100,000. Data showing the use of nitrates throughout the country were collected for the period 1945-1972. A high correlation has been found between death rates and cumulative per capita exposure to nitrogen fertilizers. Controlling for confounding socio-economic variables, estimated by housing and infant mortality rates, the correlation holds at a significant level. A negative correlation between stomach cancer and infant mortality rates, low correlation with housing rating, and a negative correlation with lung and cervical cancer deaths were also found. The latter reinforces the lack of association with socio-economic conditions. Other major sites show a completely different pattern. The epidemiological evidence presented agrees with biochemical findings on the synthesis of nitrosamines.