Nitrate, nitrite and N‐nitrosamines

Summary The major part of nitrate ingested by normal individuals from vegetables, water supplies, etc., is excreted unchanged. Where the stomach is colonised by bacteria however, as in achlorhydria, reduction to nitrite can occur with consequent methaemoglobinaemia. This problem is particularly marked in infants during the first few months of life if water supplies are rich in nitrate. Of greater potential importance to the majority of adults, however, is the formation within the body of N‐nitroso compounds, the great majority of which are carcinogenic in experimental animals. A proportion of ingested nitrate is reduced microbiologically within the mouth to nitrite which then enters the acidic milieu of the normal stomach. Bacterial colonisation of the stomach occurs increasingly in old age, and is accompanied by the formation of increased levels of nitrite and N‐nitroso compounds. Ascorbic acid is also ingested from many vegetables and is an inhibitor of the nitrosation process. Nevertheless, it is suggested that individuals with hypochlorhydria who may be particularly at risk from the formation of N‐nitroso compounds in vivo should supplement their intake of this potentially protective agent.