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What are the sources of nitrite and nitrate?

Green leafy and root vegetables, such as spinach and carrots, provide more than 85 percent of dietary nitrate, which may be converted to nitrite by the human body during digestion. Though the majority of ingested nitrate is cleared rapidly from the body via excretion, some of it is transported to the salivary glands and secreted in the mouth. There it may be reduced by existing bacteria to nitrite and carried to the stomach upon swallowing.

Dietary nitrate may also come from drinking water. Most national drinking water authorities have set a maximum limit for nitrate in drinking water to prevent high intake. The levels of nitrate in water vary greatly and may be quite high in some localities. Nitrate content in both drinking water and vegetables can be influenced by the use of nitrate fertilisers.

Foods to which nitrite is added include bacon, fermented sausage, hot dogs, bologna, salami, corned beef, ham, and other products such as smoked or cured meat, fish, and poultry. On the whole, however, the dietary intake of nitrite from cured meats is only a minute fraction of the body's total exposure. A significant amount of nitrite in the body is produced endogenously (internally), rather than introduced from dietary sources.