Information about nitrate sources of food.

From the California Extenstion program. Link to source

The average daily intake of nitrate is around 100 mg and about 12 mg for nitrite. Vegetarians have a much higher daily intake (about 250 mg) because of the high nitrate content of vegetables. Less than 10 percent of the nitrates we ingest come from our drinking water; most are found in our food. Approximately 9 percent of the nitrates we ingest come from processed meats where it is used as a preservative and as a coloring agent. The greatest amount of nitrates we encounter come from vegetables like lettuce and spinach. A little over one-fifth of the nitrites we ingest come from cured meats. The highest levels originate in our own saliva, where bacteria in our mouths change nitrates to nitrites.

Vegetables and cured meats are the main source of nitrates in our diet. Vegetables with high levels of nitrates include lettuce with averages of 850 parts per million (ppm), celery at 2340 ppm, spinach at 1860 ppm, beets at 2760 ppm, and broccoli at 780 ppm. There are many factors which affect the nitrate levels in plants. The species and variety of plant are very important. Nitrate levels also vary with the part of the plant (leaf, stem, root, etc.) and maturity of the plant. Environmental factors include; drought, high temperature, shading, nutrient deficiencies, excessive fertilizers, and plant damage from insects and herbicides. The average American ingests 86 mg of nitrate a day from vegetables alone; 18.9 mg from lettuce, 16 mg from celery, 4.2 mg from spinach, 5.5 mg from beets, and 14.2 mg from potatoes. Although it would appear that vegetables would be a high risk factor in nitrate poisoning, very few cases have ever been documented. This could be because of the ascorbic acid content of most vegetables, which have protective effects against nitrate poisoning.

Cured meats account for 15.5 mg of nitrate in the American daily diet. They also account for about 4 mg of nitrite a day. Nitrates and nitrites are used on cured meats to give it the distinctive pink color, to prevent rancidity, and to prevent the growth of Clostridium botulinum spores. Nitrate and nitrite levels in cured meats have been set by the FDA at 120 ppm. The FDA also recommends 550 ppm ascorbate or sodium erythorbate which have similar effects as ascorbic acid in vegetables.