Risk of colorectal and other gastro-intestinal cancers after exposure to nitrate, nitrite and N-nitroso compounds: A follow-up study

N-nitroso compounds are potent carcinogens detected in foodstuffs, The impo rtance of dietary nitrosamines in relation to human cancer development is, however, uncertain, We studied the relationship between intake of nitrates, nitrites and N-nitrosodimethylamine (NDMA) and risk of cancers of the gast ro-intestinal tract in a cohort of 9,985 adult Finnish men and women. Durin g a follow-up period of up to 24 years, 189 gastro-intestinal cancer cases were diagnosed in the cohort, initially free from cancer. Intake of nitrate , nitrite and NDMA were estimated, based on food consumption data from a 1- year dietary history interview covering the total diet of the participants. A significant positive association was observed between intake of NDMA and subsequent occurrence of colorectal cancer with a relative risk (RR) betwe en the highest and lowest quartiles of intake of 2.12 [95% confidence inter val (CI) 1.04-4.33]. Of various sources of N nitroso compounds, intake of s moked and salted fish was significantly (RR 2.58, 95% CI 1.21 - 5.51) and i ntake of cured meat was non-significantly (RR = 1.84, 95% CI 0.98-3.47) ass ociated with risk of colorectal cancer. No similar association was observed for intake of other fish or other meat. No significant associations were o bserved between NDMA intake and cancers of the head and neck combined or of the stomach or between nitrate or nitrite intake and risk of cancers of th e gastro-intestinal tract. Our results are in line with the idea that N-nit roso compounds can induce colorectal cancer in humans. Int J. Cancer 80:852 -856, 1999, (C) 1999 Wiley-Liss, Inc.