Nitrates and nitrites in preserved meats (bacon, cold cuts) can prevent growth of Clostridium botulinum, the organism that can produce the potent botulinum toxin.
However, nitrates and nitrites have been shown to have adverse effects, such as methemoglobinemia and carcinogenesis, the latter resulting from the formation of nitrosamines. Coincidentally, reduction of nitrate to nitrite is a common reaction for bacteria in the GI tract. Usually, the GI effect on nitrite is preceded by nitrate being reduced to nitrite by microflora of mouth saliva. The minimum nitrate intake for a person is estimated at 75 mg/d. The resulting nitrite can oxidize hemoglobin to methemoglobin, which results in the loss of oxygen-binding ability. Consequently, dietary or water sources of nitrate and nitrite can have life-threatening effects (methemoglobinemia), particularly in young children. NADH reductase is the major enzyme responsible for the reduction of methemoglobin. Because of a transient deficiency of NADH reductase, newborns are very sensitive to nitrate and nitrite toxicity.
The fatal dose of potassium nitrate for adult humans is 30 to 35 g consumed as a single dose; the fatal dose of sodium nitrite is 22 to 23 mg/kg body weight. There is no confirmable evidence in the literature on the carcinogenicity (cancer-causing capacity) of nitrate as such. capacity) of nitrate as such.
It is also notable that people normally consume more nitrates from their vegetable intake than from cured meat products. Spinach, beets, radishes, celery, and cabbages are among the vegetables that generally contain very high concentrations of nitrates.
It has been estimated that 10% of the human exposure to nitrite in the digestive tract comes from cured meats and 90% comes from vegetables and other sources. Nitrates can be reduced to nitrites by certain microorganisms present in foods and in the GI tract. This has resulted in nitrite toxicity in infants fed vegetables with a high nitrate level. Nitrites react with secondary amines to form a variety of nitrosamines. The amines necessary for the nitrosation reaction occur widely in the human diet and many foods contain sufficient amounts of nitrosamines. Certain nitrosamines induce cancers in the liver, kidney, bladder, GI tract, pancreas, and respiratory tract. Activation of nitrosamines is through cytochrome P450. The most common compound formed is diethylnitrosamine a powerful carcinogen.