"Epidemiologic studies have yet to link nitrates and nitrites to cancer in humans. One reason is that nitrosamines occur in the ppb or part per trillion range. Doses in the ppm or parts per thousand were needed to induce the cancers in animals. High consumption of cured meats has been associated with certain cancers, however, high consumption often indicates a lack of fresh food and vegetables which provide protective effects against nitrosamines. The production of nitrosamines is inhibited by vitamins A and E, sulfamate, butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), gallic acid, and various amino acids and proteins."
"In summary, nitrates do not pose a great risk to the general public. Nitrates and nitrites can cause some health problems, but only at very high levels. Compared to the amount we receive in our food, the normal levels of nitrates in drinking water should not be a concern. An exception to this is in the case of infants and a few rare susceptible adults who are consuming water with levels above the 45 ppm limit. Infants are highly susceptible to nitrate poisoning due to a number of factors not applicable to older children or most adults. Presently, methemoglobinemia would appear to be the only health problem linked to nitrates and nitrites for humans."