What you need to know about nitrates and nitrites

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Do you worry about eating foods containing nitrates and nitrites, such as cured or processed meat like bacon, ham, and salami? Have you heard they may cause cancer?

Are you confused by reports that these compounds, also found naturally in many vegetables, can also be good for you?

This guide will help you sort through the confusion and sift the facts from fears surrounding nitrates and nitrites.

The good news is that these days you don’t need to worry too much about them in your diet, and indeed they may even be beneficial to your health. Read on to understand why.


What are nitrates and nitrites?

Nitrates and nitrites are natural compounds made up of nitrogen and oxygen. The difference is in their chemical structure. Nitrates contain one nitrogen and three oxygen molecules (NO3). Nitrites have one nitrogen and two oxygen molecules (NO2).

In the body, there is a nitrate -> nitrite -> nitric oxide pathway which means a nitrate can turn into a nitrite, which can turn into nitric oxide (NO).1

While nitrates are fairly stable, nitrites and nitric oxide are not. Under certain conditions — such as high-heat cooking — nitrites/nitric oxide can sometimes convert to compounds called nitrosamines. These are the ones that give nitrates their bad rap.

What can be confusing is that nitrates and nitrites have potential positive effects in the body. However, their by-products, nitrosamines, have been deemed probable carcinogens, meaning that with repeated, high-level exposure they may cause cells to turn cancerous.2

Takeaway

Nitrates and nitrites are chemical compounds found commonly in nature with potentially beneficial health effects. Through various reactions, nitrates/nitrites may sometimes convert to compounds called nitrosamines, which may have potentially harmful health effects.


Sources of nitrates and nitrites

Nitrates/nitrites are found naturally in our bodies, including in saliva, the gut, and throughout our circulatory system.

In our body, the nitrate -> nitrite -> nitric oxide pathway is involved in cell signaling, blood pressure regulation and the functioning of the digestive system.3

We regularly encounter nitrates/nitrites from vegetables, processed foods, cured meats, cheese, drinking water, cosmetics, alcoholic beverages, rubber, air pollution, and cigarette smoke.4

For more than two thousand years, human cultures, including the ancient Romans and Chinese, have added nitrates/nitrites to cured meats and other foods to preserve them, to add flavor, or to prevent having the food oxidize and turn brown. Have you heard of saltpeter? That was one of the most common forms of nitrate/nitrite added throughout history.5

Processed meats like bacon, ham, hotdogs, and cold cuts often get criticized for being significant sources of nitrates/nitrites. However, in recent years, new curing processes have greatly diminished the active nitrate levels in these products. One of these techniques includes adding vitamin C (ascorbic acid), which inhibits the creation of nitrosamines.

Now the average person’s exposure from cured meat is only about 6% of all sources.6 You may be surprised that 85% of the nitrates and 30% of the nitrites you eat come from fresh fruit and vegetables.7

Takeaway

Nitrates and nitrites are found naturally in the human body, soil, water, fruits, and vegetables. They are also added to meats and processed foods as a preservative and to enhance flavor and color. In recent years, the amount of nitrates/nitrites in cured meats has been reduced substantially by new curing processes.


How did we come to fear nitrates and nitrites?

How did nitrates and nitrites get such a bad rap?

It was known by the 1940s and ‘50s that very high concentrations of nitrates and nitrites in drinking water, such as the contamination of well water around farms, could be deadly to fish, animals, and young children.8

The possible safety concerns around added nitrates/nitrites in processed meat grew over decades, starting in the 1970s, when experts suggested that nitrites converting to nitrosamines might be linked to oral and gastric cancers.9

In the following decades, animal and lab studies furthered the concern about the possible cancer causing nature of nitrosamines.10

However, human epidemiologic and observational studies over those years were inconsistent, or, for those that did show an association, the impact was very small, almost negligible.

In recent years no associations have been found in oral and gastric cancers and only a 1.5 risk was found for thyroid and brain cancers. (As a reminder, nutritional epidemiology results with a risk below 2.0 are frequently found to be statistical noise rather than true cause and effect).11

That means that those who ate the most processed meats with nitrates had only a one-and-a-half times higher risk of developing cancer than those who ate the least. (In contrast, the hazard ratio for cigarette smoking and lung cancer is consistently found to be more than 20, meaning people who smoke regularly over many years are 20 times more likely to get a form of lung cancer than those who don’t.)12

In 2015, however, the International Agency for Research on Cancer (IARC), which is the specialized cancer agency of the World Health Organization, classified processed meats as “carcinogenic” (and red meat as “probably carcinogenic”) in humans.

As Diet Doctor’s Guide to red meat notes, with such low hazard ratios, it’s difficult to exclude other factors that may have impacted the results, such as sugar consumption, alcohol intake, smoking, sedentary lifestyle, etc. This is called the healthy user bias.13

Since 2015, many in the scientific community have criticized the IARC decision, noting that good research is unable to show a cause-and-effect relationship between processed meat and cancer. They argue that the carcinogen classification of processed meats should be reconsidered.14

A 2019 review and meta-analysis of cohort studies found that very weak evidence (“low-certainty evidence” in the authors’ words) suggested that reducing the intake of processed meat by 3 servings per week was associated with a very small reduction in overall cancer mortality over a lifetime.15

Diet Doctor: Warnings about processed meat fail the test of science

Takeaway

The IARC named nitrates and nitrites in processed meat as a carcinogen in 2015 using weak observational data. That controversial ruling has been questioned in recent years by many scientific researchers who argue that the carcinogenic label should be re-evaluated and that the current risk of cancer from nitrates or nitrites in processed meat is very small to non-existent.


The potential health benefits of nitrates/nitrites

Can eating nitrates and nitrites be actually good for you? Emerging research is saying yes.

A 2018 meta-analysis of human studies found evidence for the following beneficial effects of nitrate/nitrite consumption on cardiovascular health:16

  • reducing resting blood pressure
  • improving the function of the lining of blood vessels
  • reducing blood vessel inflammation
  • reducing the narrowing of blood vessels
  • reducing stiffness of arteries
  • reducing the risk of blood clot formation.
The 2018 authors concluded that consuming dietary nitrates, or taking them as a supplement, may represent a simple strategy for improving cardiovascular disease risk factors. This likely occurs due to the conversion to nitric oxide.

In fact, some researchers conclude, albeit with a good deal of controversy, that because of their conversion to nitric oxide in the body, nitrates and nitrites should be considered nutrients, just like vitamins.17

However, other researchers say the findings are not yet conclusive and more studies are needed to clearly discern the pros and cons of nitrates for heart health.18

Just like vitamins, researchers note the right dose is important. Too high amounts of nitrates could be detrimental to health and too low amounts could create a deficiency of an essential substance.19 Remember, it isn’t necessarily the nitrates and nitrites we want to avoid, rather it is the nitrosamines that they can convert into.

In the sports world, consuming nitrates, such as in a concentrated beetroot or spinach juice, is being researched by many different competitive fields. While again, results are deemed very preliminary and at times inconclusive, some studies show dietary nitrates have a role in improving endurance, reducing muscle fatigue, increasing muscle contraction strength, and improving athletic performance.20

Takeaway

In the last decade the nitrate -> nitrite -> nitric oxide pathway increasingly is considered beneficial to human health. The status of nitrates/nitrites is switching from potentially carcinogenic compounds to potentially beneficial nutrients, especially for cardiovascular health and muscle function. However, more conclusive research is needed.


Minimizing nitrosamine exposure

If you enjoy eating a variety of foods, you likely don’t need to avoid vegetables or processed meats just because they may contain nitrates or nitrites.

Meat producers now by law must limit the amount of nitrates and nitrites in their processed meat products. Most now add vitamin C to their products to inhibit nitrosamine formation.21

But if you are concerned about limiting your exposure to unstable and potentially damaging nitrosamines, these tips can keep your nitrates from converting into nitrosamines.

  1. Watch cooking methods: Slower cooking and lower temperatures create fewer nitrosamines. Avoid charring or high heat frying. This also reduces the exposure to other potentially carcinogenic compounds called heterocyclic amines (HAs).22 A study from the 1970s found that bacon cooked in a microwave had lower nitrosamine conversion than in a frying pan.23
  2. Consume vitamin C and E: It has been known for three decades that the conversion of nitrites into unstable nitrosamines is inhibited by the presence of vitamin C or other antioxidants such as vitamin E.24 While it is unclear how much this helps in the human digestive tract, eating vitamin-rich foods should be entirely safe. Low-carb foods with high amounts of vitamin C include peppers, spinach, tomatoes, cauliflower, broccoli, and Brussels sprouts. Foods with high amounts of vitamin E include sunflower seeds or oil, avocado, asparagus, almonds, beet, or collard greens.
  3. Read labels: While processed meat manufacturers now have to limit the amount of synthetic nitrates/nitrites in their products and add vitamin C, if they use so-called natural sources, such as celery juice, they are allowed to label them “organic” or “no nitrate added.” These products may in fact contain more nitrate than conventional processed meat and may not inhibit bacterial growth as effectively.25
  4. Don’t smoke or chew tobacco: What is the biggest voluntary source of nitrosamine exposure? Tobacco. Instead of worrying about nitrates converting to nitrosamines in your diet, ditch tobacco products and you will greatly reduce your exposure levels to potentially carcinogenic nitrosamines.26

    Summary

    When examining the nitrate/nitrite research, advice to avoid them to reduce your risk of cancer may not hold up to closer inspection.

    Today, the average person gets most of their nitrate/nitrite intake from fresh fruit and vegetables. The amount of added nitrates in processed meats is now strictly regulated and significantly below typical levels of the 1960s and ‘70s.

    The bottom line is that you probably don’t need to worry too much about them in your diet. If you are still concerned, you can minimize your nitrosamine exposure by putting our four tips into practice.

    This guide is by Valerie Goldstein, RD with research support and editing by Anne Mullens.

     

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    More

  1. Nature Reviews 2008: The nitrate–nitrite–nitric oxide pathway in physiology and therapeutics [expert review, ungraded]

  2. Cancer Research 1983: Formation and occurrence of nitrosamines in food [expert review, ungraded]

  3. Nature Reviews 2008: The nitrate–nitrite–nitric oxide pathway in physiology and therapeutics [expert review, ungraded]

  4. Chemosphere 2018: Critical review of major sources of human exposure to N-nitrosamines [expert review, ungraded]

  5. Food and Cosmetics Toxicology 1975: The history and use of nitrate and nitrite in the curing of meat [expert review, ungraded]

  6. Chemosphere 2018: Critical review of major sources of human exposure to N-nitrosamines [expert review, ungraded]

  7. The nitrate/nitrite content from fruit and vegetables can vary greatly, even within the same type of vegetables. For example, the nitrate content in spinach can range from 71 mg to 428 mg/100g. This is caused by varying amounts of nitrogen in fertilizers, soil, air, and water, as well as, through growing, harvesting, and storage conditions.

    Nutrition Reviews 2012: Inorganic nitrate: a major player in cardiovascular health benefits of vegetables? [expert review, ungraded]

    The American Journal of Clinical Nutrition 2009: Food sources of nitrates and nitrites: the physiologic context for potential health benefits. [expert review, ungraded]

    PLOS ONE, 2020. The nitrate content of fresh and cooked vegetables and their health-related risks. [expert review, ungraded]

  8. American Journal of Public Health 1951: Survey of literature relating to infant methemoglobinemia due to nitrate-contaminated water [expert review, ungraded]

    Nitrates in contaminated water react with bacteria in the infant’s stomach, leading to a condition called methemoglobinemia, in which red blood cells’ ability to carry oxygen in the blood is blocked. This condition can deprive the infant’s tissues of oxygen, potentially leading to death. Older children and adults are not so much at risk because of their larger size.

    Current Problems in Pediatric and Adolescent Health Care 2019: Methemoglobinemia: Infants at risk [expert review, ungraded]

  9. Federal Proceedings 1976: Nitrates, nitrosamines and cancer [expert review, ungraded]

  10. Proceedings of the Society of Experimental Biology and Medicine 1997: Approaches to cancer prevention based on an understanding of N-nitrosamine carcinogenesis [expert review, ungraded]

  11. Oncotarget 2016: Association between dietary nitrate and nitrite intake and specific cancer risk: evidence from observational studies [meta analysis of observational studies, weak evidence]]

  12. American Journal of Epidemiology 2018: Sex differences in risk of smoking-associated lung cancer: Results from a cohort of 600,000 Norwegians [observational study, weak evidence]

    International Journal of Cancer 2013: Cigarette smoking and lung cancer – relative risk estimates for the major histological types from a pooled analysis of case-control studies [pooled observational study, weak evidence]

  13. Journal of General Internal Medicine 2011: Healthy user and related biases in observational studies of preventive interventions: a primer for physicians. [expert review, ungraded]

  14. Nutrients 2019. A review of the in vivo evidence investigating the role of nitrite exposure from processed meat consumption in the development of colorectal cancer. [review article; ungraded]

  15. Annals of Internal Medicine 2019: Reduction of red and processed meat intake and cancer mortality and incidence: A systematic review and meta-analysis of cohort studies [meta-analysis, weak evidence]

  16. Nutrition Review 2018: The role of inorganic nitrate and nitrite in cardiovascular disease risk factors: a systematic review and meta-analysis of human evidence. [strong evidence]

  17. American Journal of Clinical Nutrition 2009: Food sources of nitrates and nitrites: the physiologic context for potential health benefits. [expert review, ungraded]

  18. JBI Database of Systematic Reviews and Implementation Reports: 2019 Effectiveness of dietary inorganic nitrate for lowering blood pressure in hypertensive adults: a systematic review. [expert review, ungraded]

  19. Nutrition Research Review 2017: Dietary nitrate and blood pressure: evolution of a new nutrient? [expert review, ungraded]

  20. Frontiers in Physiology 2019. Dietary nitrate supplementation improves exercise tolerance by reducing muscle fatigue and perceptual responses. [expert review, ungraded]

     

    European Journal of Sports Science 2019: Potential benefits of dietary nitrate ingestion in healthy and clinical populations: A brief review [expert review, ungraded]

  21. Meat Science 2007: The use and control of nitrate and nitrite for the processing of meat products [expert review, ungraded]

  22. The Journal of Nutrition 2004: Development of a food database of nitrosamines, heterocyclic amines, and polycyclic aromatic hydrocarbons [expert database, ungraded]

  23. Journal of Food Science 1974: Effect of frying and other cooking conditions on nitrosopyrrolidine formation in bacon [lab study, very weak evidence]

  24. American Journal of Clinical Nutrition 1991: The preventive action of ascorbic acid on nitrosamine formation. [expert review, ungraded]

  25. Meat Science 2007: Cured meat products without direct addition of nitrate or nitrite: what are the issues? [expert review, ungraded]

  26. Journal of Physiology and Biochemistry 2016: Tobacco nitrosamines as culprits in disease: mechanisms reviewed [expert review, ungraded]