The Agency for Toxic Substances and Disease Registry adds that if you consume unusually high levels of nitrates or nitrites, it can lead to a condition called methemoglobinemia, which is a decreased ability for your red blood cells to carry oxygen to your tissues.
This can cause several symptoms, including drops in blood pressure, increased heart rate, headaches, abdominal cramps and vomiting, and in severe cases, death.
However, exposure to levels of nitrates that high are extremely rare and, again, adverse health effects are most commonly associated with synthetic nitrates.
Naturally occurring nitrates and nitrites don't present the same issue because they're often coupled with nutrients like vitamin C and antioxidants that prevent them from converting into nitrosamines. Vegetables are actually the highest source of natural nitrates, while fruits trail somewhere behind them.
The vegetables that are the highest in nitrates include:. Some fruits do contain nitrates, but the amounts are generally low. The fruits that do contain nitrates include:.
The report in Aging and Disease points out that approximately 80 to 90 percent of dietary nitrates come from green, leafy vegetables. The second biggest source is drinking water, which provides 15 to 20 percent of daily intake.
The Agency for Toxic Substances and Disease Registry adds that, besides fruits and vegetables, other food and drink sources of nitrates include:. Although you don't have to worry about the nitrates found in fruits and vegetables, which also provide many other beneficial nutrients, it is a good idea to lower your intake of nitrates and nitrates that are added to food during processing.
The Environmental Working Group provides some tips for avoiding added nitrates in your diet:. Nutrition Fruits and Vegetables Other Fruit.
Lindsey is the owner and founder of Rise Up Nutrition helping athletes overcome disordered eating to perform at their highest level www. To decrease your risk of colon cancer, it is a good idea to eat very little processed meats or avoid them altogether. It depends on the food. Organic foods like vegetables and fruit typically have fewer nitrates compared to conventional foods. However, processed organic meats do not have nitrates. In Canada, adding nitrates to processed organic meats is not allowed.
Read more about organic foods in Canada. Nitrates are naturally found in some vegetables, dairy products and meat. There is no recommendation to limit foods that naturally contain nitrates. Nitrates are also added to processed meats as a preservative. Food Additives. Dietitians look beyond fads to deliver reliable, life-changing advice. Want to unlock the potential of food?
Connect with a dietitian. What are nitrates? Where are nitrates found? Nitrates are naturally found in vegetables such as: Beets Celery Lettuce Radishes and Spinach These foods provide the most nitrates in our diets. Given the complex interactions between nitrite and nitrate of dietary origin, the endogenous production of nitrate and nitrite from nitric oxide and other nitrogen oxides NO x Figure 1 , the effect of physiologic conditions such as atherosclerosis and inflammatory disease, dietary sources of NO x , and physical activity, nitrate, and nitrite balance studies are not, at present, feasible.
Therefore, a simple characterization of an optimal concentration of dietary nitrate and nitrite based on an overall picture of the nitrate and nitrite economy is not possible. However, we can make 2 generalizations that summarize our current knowledge. First, most nitrite utilization and nitric oxide production occur in healthy individuals in 2 compartments: vascular and somatic tissues. Normal vascular function requires nitric oxide production from the l -arginine-NOS pathway; in ischemic conditions, nitrite can substitute for l -arginine-NOS-derived nitric oxide 31 , Most healthy somatic tissues possess mammalian enzymes that exert nitrate reductase activity the tongue utilizes nitrate reductases of commensal bacteria to generate biologically active nitrite to maintain gastrointestinal and cardiovascular health.
In inflammatory conditions, iNOS in epithelial and immune cells can produce nitric oxide as part of the innate immune response. However, concern has been expressed that nitrite may be reduced to nitric oxide under normoxic conditions 63 and that, under these conditions, nitrate and nitrite may inhibit steroidogenesis in vitro and in vivo The data supporting the in vivo conversion of nitrates and nitrites to nitric oxide has implications for dietary consumption of foods high in nitrate and nitrite.
As such, nitrate- and nitrite-containing foods may supply nitrite in situations in which substrates for endogenous NO x production are limiting, as in cardiovascular conditions, to support cardiovascular and gastrointestinal function.
As such, when the dietary intake of nitrate and nitrite is low and there is no additional endogenous sources of NO x eg, gastrointestinal infections involving iNOS activation , the endogenous production of nitrate, via oxidation of nitric oxide and nitrite, provides more substrate for nitric oxide production than dietary sources. Dietary nitrate intake is determined by the type of vegetable consumed, the levels of nitrate in the vegetables including the nitrate content of fertilizer , the amount of vegetables consumed, and the level of nitrate in the water supply As such, the nitrate content of organic vegetables may be less than that of vegetables grown in the presence of nitrogen-containing fertilizers.
The primary determinants of nitrite consumption are the levels of nitrites in cured, processed meats and the consumption level of these products. The nitrate and nitrite contents of edible vegetable components are listed in Table 2 from reference A list of vegetable varieties grouped in ascending order of nitrate content are shown in Table 3 from reference The accumulation of nitrate is subject to factors such as genotype, soil conditions, growth conditions ie, nitrate uptake, nitrate reductase activity, and growth rate , and storage and transport conditions 65 , For example, the average nitrate content of spinach collected from 3 different markets in Dehli, India, varied from 71 to These data dictate that caution be observed in linking the biological effects of leafy vegetables and other nitrate-containing vegetables and fruit to specific health effects, particularly in observational epidemiologic studies.
Nitrate and nitrite contents of edible components of vegetables 1. Data from reference Classification of vegetables according to nitrate content 1. The mean intake estimates for nitrate and nitrite in the United States and Europe vary by investigator but are consistent and comparable.
Due to the variability in nitrate and nitrite concentrations of foods reported in Tables 2 and 3 , we conducted nitrate and nitrite analyses on a convenience sample of vegetables, a commercial vegetable juice beverage V8; Campbell Soup Co, Camden, NJ , fruit, fruit juices, as well as fresh and processed meats Tables 4 and 5. Mean nitrate and nitrite contents of a convenience sample of fruit, vegetables, meats, and processed meats 1. Analysis of foods reflects the mean value from triplicate or quadruplicate analyses.
We set out to model this variation by using the vegetable and fruit components of the DASH dietary pattern 73 that involved choosing particular foods with a high or low nitrate content. The high-nitrate DASH diet would result in the consumption of mg nitrate and 0. Hypothetical dietary nitrate and nitrite intakes based on food and juice serving recommendations for vegetables and fruit based on the Dietary Approaches to Stop Hypertension DASH dietary pattern 1.
Analysis of foods reflects the mean value from triplicate analyses. Analogous to all essential or indispensable nutrients, intake of excess nitrate and nitrite exposure is, in specific contexts, associated with an increased risk of negative health outcomes. A set of Dietary Reference Intake DRI categories are set by the Food and Nutrition Board of the National Academy of Sciences for essential nutrients to clearly define, where possible, the contexts in which intakes are deficient, safe, or potentially excessive.
The process of setting DRIs for nutrients considers a broad range of physiologic factors, including nutritional status and potential toxicities. Rational methodologies such as these, including the consideration of normal dietary consumption patterns of nitrate- and nitrite-containing foods, have not been applied in setting exposure limits or in considering the potential health benefits of dietary nitrates and nitrites.
Whereas accidental toxic exposures of nitrates and nitrites have occurred 75 , the health risks due to excessive nitrate and nitrite consumption appear only in specific subgroups of the population. Two types of exposure place susceptible individuals at high risk to the adverse effects of excess nitrite exposure. First, infants younger than 6 mo of age may be exposed to excess nitrates in bacterially contaminated well water, which reduces nitrate to nitrite As such, an American Academy of Pediatrics consensus panel concluded that all prenatal and well-infant visits should include questions about the home water supply; if the water source is a private well, the water should be tested for nitrates The panel concluded that infants fed commercially prepared infant foods are generally not at risk of nitrate poisoning, but that home-prepared infant foods from vegetables eg, spinach, beets, green beans, squash, and carrots should be avoided until infants are 3 mo of age or older.
Breastfed infants are not at risk of excessive nitrate exposure from mothers who ingest water with a high nitrate content up to ppm nitrate nitrogen because the nitrate concentration does not increase significantly in breast milk Note that the few human nitrate and nitrite exposure studies, including children and adults, have not produced methemoglobinemia. A more recent randomized 3-way crossover study exposed healthy adults to single doses of sodium nitrite that ranged from to mg per volunteer to — mg per volunteer The observed methemoglobin concentrations were These data have led scientists to propose alternative explanations for the observed methemoglobinemia in infants, including gastroenteritis and associated iNOS-mediated production of nitric oxide induced by bacteria-contaminated water 83 , These studies call into question the mechanistic basis for exposure regulations for nitrate and nitrite.
At best, these findings highlight a serious, but context-specific, risk associated with nitrite overexposure in infants. Experts have questioned the veracity of the evidence supporting the hypothesis that nitrates and nitrites are toxic for healthy adolescent and adult populations 16 , 17 , It appears that the biologically plausible hypothesis of nitrite toxicity eg, methemoglobinemia has essentially transformed a plausible hypothesis into sacrosanct dogma 16 , despite the lack of proof 83 , The second context in which nitrate and nitrite exposure has been associated with negative health effects is through the consumption of cured and processed meats Nitrates added to meats serve as antioxidants, develop flavor, and stabilize the red color in meats but must be converted to nitrite to exert these actions.
Sodium nitrite is used as a colorant, flavor enhancer, and antimicrobial agent in cured and processed meats. Nitrate and nitrite use in meat products, including bacon, bologna, corned beef, hot dogs, luncheon meats, sausages, and canned and cured meat and hams is subject to limits put forth in Food and Drug Administration FDA and US Department of Agriculture USDA regulations. Consumption of red and processed meats is associated with an increased risk of certain types of cancer and chronic obstructive pulmonary disease 85 — It is worth noting that nitrite or nitrate is not added to fresh meats.
A discussion of this association in the context of nitrate and nitrite consumption and gastric physiology is warranted to illuminate the processes relevant to this association. Direct evidence of the participation of nitrate and nitrite in human carcinogenesis is lacking, despite extensive epidemiologic and animal studies Rodent toxicological studies 91 and human epidemiologic investigations have not shown an unequivocal relation between nitrite exposure and the risk of cancer It is reasonable to conclude that all food sources of nitrate and nitrite are not equal with regard to potential health benefits or risks.
The association between nitrite consumption and gastrointestinal cancers was bolstered by findings that ingested nitrites may react with secondary amines or N -alkylamides to generate carcinogenic N -nitroso compounds NOCs Although NOCs have been shown in animal models to be carcinogenic 92 , proof in humans has been scant. The N -nitrosamides and N -nitrosoureas have been shown to be direct mutagens, whereas N -nitrosoamines do not act as direct mutagens but generally require activation by microsomal enzymes within the body, perhaps by cytochrome P enzymes The use of nitrites in bacon must be accompanied by the use of either sodium erythorbate or sodium ascorbate vitamin C , antioxidants that inhibit the nitrosation effect of nitrites on secondary amines A recent study has yielded new insights into the ability of vitamin C to modulate the formation of carcinogenic NOCs under conditions simulating the proximal stomach during the digestion of foods such as processed meats Nitrite in processed meats may be converted to nitrosating species and NOCs by acidification in the presence of thiocyanate at low gastric pH.
The formation of NOCs was examined under these conditions in the presence and absence of vitamin C and lipid. In the absence of lipid, vitamin C prevented the formation of N -nitrosodiethylamine and N -nitrosopiperidine and decreased the formation of N -nitrosodimethylamine and N -nitrosomorpholine 5-fold and fold, respectively.
Thus, the presence of lipid converts vitamin C from inhibiting to promoting acid nitrosation. This effect is attributable to the ability of vitamin C to assist in the generation of nitric oxide in the aqueous phase, which enables the regeneration of nitrosating species by reacting with oxygen in the lipid phase Whereas these data require confirmation in animal models and in humans, it provides a biologically plausible mechanism for the observed association between processed meat consumption and gastrointestinal cancer risk.
Others have postulated that gastric formation of NOCs may be inhibited by nutrients and other components of vegetables and fruit Clearly, more research is needed to address the potential mechanisms by which certain NOCs are related to cancer risk.
The recent demonstration of the vasoprotective, blood pressure—lowering, and antiplatelet aggregation properties of nitrite alone, or of nitrite originating from dietary nitrate, suggests that a reexamination of the health effects of dietary sources of nitrate and nitrite would be beneficial 31 , 32 , An illustrative example of human exposure to nitrate, nitrite, and nitric oxide will serve to support the apparent safety of these exposure levels.
Based on an estimated daily intake of 0. A kg individual produces 1. Notably, the amount of nitrite and nitrate consumed as dietary nitrate and nitrite results in nitric oxide production approximately equal to endogenous sources if, as discussed above, we assume most of the endogenous nitric oxide goes to stepwise oxidation to nitrite and nitrate.
The enterosalivary concentration and circulation of nitrate and ultimately nitrite provides an essential pathway for health and host defense Even more convincing, studies of natives in the high altitude of Tibet have shown that increasing nitrite and nitrate concentrations within the body is a natural physiologic response that is not associated with harmful physiologic effects These data show that normal physiologic exposure levels of nitrite and nitrate greatly exceed concentrations considered to produce health risks.
These observations render as questionable the rationale supporting these regulatory limits. In fact, as has been observed previously and confirmed here, a portion of spinach commonly consumed in one serving of salad can exceed the ADI for nitrate The fact that typical consumption patterns of vegetables and fruit exceed regulatory limits for dietary nitrates calls into question the rationale behind current nitrate and nitrite regulations.
The physiologic basis for regulating human consumption of plant foods containing nitrates and nitrites should be reevaluated to include potential health benefits. Taken together, the data considered here support the conclusions of the European Food Safety Authority 66 that benefits of vegetable and fruit consumption outweigh any perceived risk of developing cancer from the consumption of nitrate and nitrite in these foods.
Note that the nitrate and nitrite concentrations measured in our convenience sample may differ from samples taken from more disparate geographic locations. We conclude that the data on nitrate and nitrite contents of vegetables and fruit bolster the strength of existing evidence to recommend their consumption for health benefits.
Despite the demonstration of physiologic roles for nitrate and nitrite in vascular and immune function, food sources of nitrates and nitrites as healthful dietary components have received little attention The questionable practice of causal inference with regard to the etiologic roles of dietary nitrates and nitrites in methemoglobinemia and cancer has exerted a detrimental effect on research supporting the health benefits of nitrate- and nitrite-containing foods.
This has occurred despite the observed benefits of nitrate and nitrite in medical therapeutics Indeed, data from observational epidemiologic and human clinical studies support the hypothesis that nitrates and nitrites of plant origin play essential physiologic roles in supporting cardiovascular health and gastrointestinal immune function.
We support the recent call for a multidisciplinary and systematic review of the biological consequences of dietary nitrate and nitrite consumption No conflicts of interest were reported. Overview of the health benefits of fruit and vegetable consumption for the dietetics professional: selected literature. J Am Diet Assoc ; : — Google Scholar. Hasler CM. Functional foods: benefits, concerns and challenges-a position paper from the American Council on Science and Health.
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