What you need to know about nitrates and nitrites
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.2 However, their by-products, nitrosamines, have been deemed probable carcinogens, meaning that with repeated, high-level exposure they may cause cells to turn cancerous.3
Nitrates and nitrites are chemical compounds found commonly in nature with potentially beneficial health effects. Through various reactions, nitrates/nitrites may convert to compounds called nitrosamines, which 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.4
We regularly encounter nitrates/nitrites from vegetables, processed foods, cured meats, cheese, drinking water, cosmetics, alcoholic beverages, rubber, air pollution, and cigarette smoke.5
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.6
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.7 You may be surprised that 85% of the nitrates and 30% of the nitrites you eat come from fresh fruit and vegetables.8
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.9
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.10
In the following decades, animal and lab studies furthered the concern about the possible cancer-causing nature of nitrosamines.11
However, human epidemiologic and observational studies over those years were inconsistent; for those that did show an association, the impact was very small – almost negligible.
In an attempt to clarify risk, a meta-analysis of observational studies was performed and found no association between nitrate/nitrite exposure and the majority of examined cancers. Gastric cancer was actually found to be less common with increasing exposure, while thyroid cancers and brain gliomas were 1.5 and 1.2 times more common, respectively.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. Most critics have noted that the strength of the evidence is weak but, even assuming that there is an association, the magnitude of the effect would be extremely small.14 Unfortunately, the classification scheme used does not take that fact into account.15
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.16
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 carcinogen label should be reconsidered 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 actually be 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:17
- 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
In fact, some researchers conclude, albeit controversially, that because of their conversion to nitric oxide in the body, nitrates and nitrites should be considered nutrients, similar to vitamins.18
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.19
Just like vitamins, researchers note the right dose is important. High amounts of nitrates could be detrimental to health, while low amounts could create a deficiency of an essential substance.20 Remember, it isn’t necessarily the nitrates and nitrites we want to avoid; rather, it is the nitrosamines into which they can be converted.
In the sports world, consuming nitrates – such as in a concentrated beetroot or spinach juice – is being researched as a performance-enhancer in several competitive fields. While results are deemed preliminary and are not all conclusive, some studies show dietary nitrates have a role in improving endurance, reducing muscle fatigue, increasing muscle contraction strength, and improving athletic performance.21
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.22
But if you are concerned about limiting your exposure to unstable and potentially damaging nitrosamines, these tips can keep nitrates from converting into nitrosamines.
- Watch cooking methods: Slower cooking and lower temperatures create fewer nitrosamines. Avoid charring or high-heat frying. This also reduces the production of other potentially carcinogenic compounds called heterocyclic amines.23 A study from the 1970s found that bacon cooked in a microwave had lower nitrosamine conversion than in a frying pan.24
- 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.25 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.
- 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, which could ultimately increase the risk of nitrosamine formation. On the other hand, because the amount of “natural” nitrates/nitrites is harder to measure and control, these products are at risk of not inhibiting bacterial growth as effectively.26
- 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.27
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.
Research suggests that these compounds can reduce blood pressure, narrowing of arteries, clot formation, and gastric ulcers, among other benefits.
The nitrate/nitrite content of fruits and vegetables can vary greatly, even within the same type of vegetable. 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 by different growing, harvesting, and storage conditions.
Methemoglobinemia is a condition in which red blood cells’ ability to carry oxygen in the blood is blocked. This can deprive an infant’s tissues of oxygen, potentially leading to death. Older children and adults are not at much risk because of their larger size.
It is now better understood that it was fecal contamination of the wells – and not so much the nitrates – that likely led to methemoglobinemia, as fecal bacteria reacted with the nitrates to form methemoglobin. Nitrate concentrations typically found in uncontaminated food and water are unlikely to cause this problem.
As a reminder, nutritional epidemiology results with a risk below 2.0 are frequently found to represent statistical noise rather than true cause and effect.
Oncotarget 2016: Association between dietary nitrate and nitrite intake and specific cancer risk: evidence from observational studies [meta-analysis of nutritional epidemiology studies with HR<2, very weak evidence]
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 develop a form of lung cancer than those who don’t.
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] ↩
The following sentiment, expressed by a scientist at the University of Cambridge, was typical of the criticisms of the IARC: “There may be good evidence for there being an increased risk, but the magnitude needs to be put into perspective. In the normal run of things, around 6 in every 100 people would be expected to get bowel cancer in their lifetime. If all these 100 people ate a three-rasher (around 50g) bacon sandwich every single day of their lives, then according to this report we would expect that 18% more would get bowel cancer – which is a rise from 6 cases to 7 cases. So that’s one extra case of bowel cancer in all those 100 lifetime bacon-eaters.” ↩
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] ↩
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] ↩