Nitrite intake

Epidemiologic studies in Japan indicate an increased risk of stomach cancer owing to consumption of broiled fish and meats (116). In the United States, stomach cancer incidence has steadily declined since the 1940s, whereas consumption of broiled food has increased (108). In addition, the average human intake of PAHs is only 0.002 of that required to produce cancer in half of animals fed. Test results are often contradictory (117) and many components of food, such as vitamin A, unsaturated fatty acids, thiols, nitrites, and even saUva itself, tend to inhibit the mutagenic activity of PAHs (118—120). Therefore, the significance of PAHs in the human diet remains unknown (121,109). 

Inhibition of Nitrosamine Formation. Nitrites can react with secondary amines and A/-substituted amides under the acidic conditions of the stomach to form /V-nitrosamines and A/-nitrosamides. These compounds are collectively called N-nitroso compounds. There is strong circumstantial evidence that in vivo A/-nitroso compounds production contributes to the etiology of cancer of the stomach (135,136), esophagus (136,137), and nasopharynx (136,138). Ascorbic acid consumption is negatively correlated with the incidence of these cancers, due to ascorbic acid inhibition of in vivo A/-nitroso compound formation (139). The concentration of A/-nitroso compounds formed in the stomach depends on the nitrate and nitrite intake. 

Van Loon AJM, Botterweck AAM, Goldbohm RA, Brants HAM, van Klaveren JD, van den Brandt PA (1998) Intake of nitrate and nitrite and the risk of gastric cancer A prospective cohort study. Br J Cancer 7 129-135... 

There have been health concerns about the presence of nitrate in food as it can be metabolised to potentially carcinogenic /V-nitroso compounds. For this reason, the European Commission s Scientific Committee on Food considered the implications for human health of nitrate in food in 1990 and set an Acceptable Daily Intake (ADI) for the nitrate ion of 0-3.65 mg/kg body weight (equivalent to 219 mg/day for a 60 kg person) and an ADI for the nitrite ion of 0-0.07 mg/kg body weight.45 These ADIs were reviewed in 1995, when the ADI was confirmed and a new ADI of 0-0.06 mg/kg body weight was set.46... 

ELLEN G, EGMOND E, VAN LOON J W, SAHERTIAN E T and TOLSMA K, Dietary intakes of some essential and non-essential trace elements, nitrate, nitrite and N-nitrosamines by Dutch adults estimated by a 24-hour duplicate portion study , Food Additives and Contaminants, 1990 7 207-22. 

The nitrate-nitrite intake from natural sources is much higher than that from processed foods. Fassett (1977) estimated that the nitrate intake from 100 g of processed meat might be 50 mg and from 100 g of high-nitrate spinach, 200 mg. Wagner and Tannenbaum (1985) reported that nitrate in cured meats is insignificant compared to nitrite produced endogenously. Nitrate is produced in the body and recirculated to the oral cavity, where it is reduced to nitrite by bacterial action. 

In addition to dietary sources, a significant amount of nitrate is formed endogenously by the metabolism of nitric oxide - 1 mg per kg of body weight per day (about the same as the average dietary intake), increasing 20-fold in response to inflammation and immune stimulation. There is considerable secretion of nitrate in saliva, and up to 20% of this may be reduced to nitrite by oral bacteria. Under the acidic conditions of the stomach, nitrite can react with amines in foods to form carcinogenic N-nitrosamines, although it is not known to what extent this occurs in vivo. 

Some additives clearly serve an important function. Preservatives help to prevent food from spoiling and enable processed food to be stored for much longer. They reduce the likelihood of bacterial contamination in the food we eat. Sodium nitrite is added to cured meat, for example, to prevent the growth of organisms like Clostridium botulinum, which causes severe toxicity, botulism (see pp. 249-51). Preservatives also reduce chemical degradation and so allow food to have a longer shelf life. Other additives may also have a beneficial function, for example artificial sweeteners reduce the sugar intake of people who suffer from diabetes or obesity. 

Tannenbaum, S., Weisman, M, and Fett, D (1976). The effect of nitrate intake on nitrite formation in human saliva. Food Cosmet Toxicol 14(6) 549-552. 

N. Fujiwara, T. Osanai, T. Kamada, T. Katoh, K. Takahashi and K. Okumura. Study on the Relationship Between Plasma Nitrite and Nitrate Level and Salt Sensitivity in Human Hypertension. Modulation of Nitric Oxide Synthesis by Salt Intake, Circulation 101 (2000) 856-864. 

Nitrates are reduced to nitrites by rumen micro-flora. In normal circumstances the nitrite ion is rapidly utilized for ammonia synthesis, but in cases of excessive acute intake of nitrate, the rapidly formed nitrite ion is absorbed into the bloodstream. In blood... 

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