Nitrates/Nitrites in Foods and Their Effects

Hydroponics—Farming without soil, which uses less water

Nitrates in Plants

Several factors influence the accumulation of nitrates in plants, which include:

• Lack of sunlight or water, variety, maturity
• High levels of fertilizers
• Excessive use of nitrogen fertilizers should be avoided so as to reduce nitrate buildup in soil and vegetables.^[5] 
• Nitrate levels in the soil, and 
• Quality of irrigation water

Nitrate is nontoxic below maximum residue levels (MRLs), but if it reaches above this level, it "could" (see more details later) be dangerous due to its reduction in nitrites, which can react with amines and amides to produce “N-nitroso” compounds responsible for gastric cancer.^[5,6] High levels of nitrates in children stomach are also responsible for methemoglobinemia (blue baby syndrome).^[7,8]

The Healthy Route to Nitrite Processing

Certain vegetables contain nitrates, which break down into nitrites when eaten. Nitrites are necessary and life-enhancing, providing the nitric oxide we need to keep our blood vessels dilated, and minimize risk of high blood pressure. 

Studies have shown that nitrites packaged in vegetables can improve oxygen efficiency and delivery by dilating blood vessels, resulting in:^[1]

• lowered blood pressure
• improved breathing for those with Chronic Obstructive Pulmonary Disease (COPD)
• decreased age-related cognitive decline
• increased blood flow in those with Peripheral Artery Disease.

The Unhealthy Route to Nitrite Processing

If nitrites are so beneficial, how can they be so harmful when consumed in meat? The answer is not in the nitrites themselves, but in how they can be converted, under certain circumstances, into nitrosamines—recognized as one of the most potent carcinogens in the world.^[1]

Research is now clarifying that nitrosamines are formed when nitrites are consumed in the absence of plants (vs. meat), because phytonutrients found in plants can block nitrosamine formation. Because meat contains none of these plant phytonutrients, when nitrites are added to meat as preservatives and colorings, nitrosamines form in processed meat.

Summary

Because phytonutrients found in plants can block nitrosamine formation, it's safer to consume plants with nitrates/nitrites than meats with added nitrates/nitrites.  However, in order to maximize the health benefits from eating vegetables, measures should be also taken to reduce the nitrate and nitrite exposures.^[9] For example, 

• Vegetables must be stored and processed properly to prevent bacterial contamination and hence reduction of nitrate to nitrite.^[10]
• Consume vegetables with high phytonutrients contents vs. low phytonutrients contents.
• Avoid processed meat because nitrites and nitrates are added to processed meat to help them maintain that nice pink color:^[2-4]
• The problem is, in the presence of heat—especially high heat—nitrites can combine with amines in processed meat to form nitrosamines, and these are carcinogenic.

References

1. Effects of agriculture production systems on nitrate and nitrite accumulation on baby-leaf salads
2. EWG Releases Dirty Dozen Guide to Food Additives (Dr. Mercola)
3. Total N-nitroso compounds and their precursors in hot dogs and in the gastrointestinal tract and feces of rats and mice: possible etiologic agents for colon cancer.
4. No risk from nitrates in vegetables, says EFSA
5. Santamaria P. Nitrate in vegetables: toxicity, content, intake and EC regulation (review) J. Sci. Food Agric. 2006;86:10–17.
6. Savino F, Maccario S, Guidi C, Castagno E, Farinasso D, Cresi F, et al. Methemoglobinemia caused by the ingestion of courgette soup given in order to resolve constipation in two formula-fed infants. Ann. Nutr. Metab. 2006;50:368–371.
7. Greer FR, Shannon M. Infant methemoglobinemia: the role of dietary nitrate in food and water. American Academy of Pediatrics Committee on Nutrition, American Academy of Pediatrics Committee on Environmental Health, 2005. Pediatrics. 2005;116:784–786.
8. Chan TYK. Vegetable-borne nitrate and nitrite and the risk of methaemoglobinaemia. Toxicol. Lett. 2011;200:107–108.
9. Correia M, Barroso A, Barroso MF, Soares D, Oliveira MBPP, Delerue-Matos C. Contribution of different vegetable types to exogenous nitrate and nitrite exposure. Food Chem. 2010;120:960–966.
10. Leszczyńska T, Filipiak-Florkiewicz A, Cieślik E, Sikora E, Pisulewski PM. Effects of some processing methods on nitrate and nitrite changes in cruciferous vegetables. J. Food Compos. Anal. 2009;22:315–321.