by Eben van Tonder 1 September 2022
Part 5 in our series, The Truth About Meat Curing: What the popular media do NOT want you to know!
The accusation is widespread in the media, sensation-seeking documentaries and celebrity chefs alike that nitrite, derived from ammonia, nitrate (Salpeter) or added in the form of sodium nitrite in meat curing is tantamount to poisoning consumers and inviting cancer into your lives. I am a meat curing professional. My interest in the truth about nitrites is in the first place to be certain that I am not engaged in an action where harmful products are produced. To state this slightly differently, what steps can I take to ensure the safest possible product is made available?
The issue of nitrites is complex and to develop even a rudimentary understanding of all the issues requires that we work through a lot of technical information. Despite this, the basic evaluation is simple and well within the grasp of the general public. Here I desire to share with you what I discovered about this remarkable compound!
It is part of a short series I’ve put together on the matter entitled, The Truth About Meat Curing: What the popular media do NOT want you to know! After preliminary discussions, we now place the spotlight squarely on nitrite. We discover that instead of poison, even though this is true in large dosages and under certain conditions, it is a vitally important compound for the normal functioning of our bodies. That the sources are mostly from vegetables and not cured meat, and that any possible harmful effect is removed through the simultaneous consumption of vitamins A, C, E, etc.
What I discovered is that an entirely different (and positive) world exists related to nitrites generally and dietary nitrites in particular. The evidence is clear, overwhelming and available to anybody with an honest interest in the matter that nitrites are beneficial to human health and essential for the optimal functioning of our bodies. We will discover that there is a seemingly unresolved issue in that while nitrites, in balanced concentrations, have overwhelmingly beneficial results in the human body (may I even call it essential?!), there is seemingly contradictory information which shows that nitrites are involved, under certain conditions in the generation of N-Nitrosamines which can be cancer-causing. Parallel to this is the indication of many studies that there seems to be a relationship between the consumption of cured meats and cancer and even though the exact reason has not been elucidated, it begs the question as to possible reasons for this. How do we deal with this seemingly contradictory information, that n-nitrosamines which are the obvious culprit for any possible link between cured meat and cancer on the one hand come from nitrites and on the other hand, nitrites play an vital part in our general health and the resolution of many common diseases and ailments? Can it be that nitrosamines are not the culprit of what seems to be a link between cancer and cured meat? Can it be that lifestyle or general nutritional habits alter the nature of an important chemical in our bodies from beneficial to harmful and if this is the case, what are those factors? Is it fair to label bacon as possibly cancer-causing? When it comes to the full array of reactive nitrogen species of which nitrite is a part, is it possible to have the one without the other, especially in light of the fact that the curing molecule is nitric oxide, also one of the reactive nitrogen species? Is the statement that curing was done with no nitrite even a sensical one in light of the oxidation of nitric oxide to nitrite and nitrite to nitrate in the curing environment? It begs the question if no nitrite curing which has been the goal of meat scientists for so many years even valid question to ask or is this something that will sell products without any real benefit to the consumer as far as the removal of the real risk of n-nitrosamine formation. This is an extremely timely question as we stand at the dawn of a time when no-nitrite curing will become a reality across the world. The emphasis is about to squarely shift to nitric oxide and in light of this future trend we have to ask, can nitric oxide contribute to nitrosamine formation as is the case with nitrites which would mean that removing nitrites from the curing system has no real benefit as far as nitrosamine formation is concerned.
We have to continue the questioning. If ingesting dietary nitrite has overwhelmingly positive effects on human physiology, should nitrite curing not rather be encouraged and embraced and should ham and bacon not be seen as a superfood instead of something to be avoided? I ask another question which is the focus of my own work and that of a small band of like-minded food professionals and scientists – how do we turn ham, bacon and the cured meats we love into superfoods in such a decisive manner that there can be no argument from any quarter about this status!? These are all valid questions and despite the mammoth task ahead, I will do my best to interact with all these questions in this document. Where I fail, please point it out to me so that I can improve on the document and evolve in my thinking, but please, do it from a position of constructive interaction and partnering with me in seeking the truth!
I will try and deal as honestly as a layman can with these complex questions, believing that I have a sacred responsibility to the consumer to do exactly this and if the evidence points away from what I would like it to say, that I should have the integrity follow the lead of the evidence. My ultimate goal is therefore the TRUTH and not to generate “likes” on social media posts. Anybody with a meaningful contribution or who wants to correct me on any point can contact me at email@example.com or WhatsApp me at +27 71 545 3029.
History of Nitric Oxide and the Close Link between Nitrate, Nitrite and Nitric Oxide.
Nitric oxide (NO) was discovered in 1772. Nitroglycerine (NG), a vasodilator acting via NO production, was synthesized in 1847. The effect of nitroglycerine was studied on healthy volunteers by Constantin Hering in 1849 and it was proven to cause headaches. Later in 1878, nitroglycerine was used by William Murrell for the first time to treat angina. Towards the end of the 19th century, nitroglycerine was established as a remedy for relief of anginal pain.” (Ghasemi, 2011) Angina is a type of chest pain caused by reduced blood flow to the heart. In 1916, Mitchell et al. suggested that body tissues can also produce nitrate and Richard Bodo in 1928 showed a dose-dependent increase of coronary flow in response to sodium nitrite administration. In the 1970s, it was shown that nitrite-containing compounds stimulate guanylate cyclase,” which is an enzyme that converts guanosine triphosphate (GTP) to cyclic guanosine monophosphate (cGMP) and pyrophosphate. An increase of cyclic guanosine monophosphate (cGMP), also caused by the intake of nitrite containing compounds cause vascular relaxation and it is presumed that cGMP activation may occur via the formation of NO. (Ghasemi, 2011)
In 1980, Furchgott and Zawadzki showed that endothelial cells are required for acetylcholine-induced relaxation of the vascular bed which refers to the vascular system or a part thereof, through the endothelium-derived relaxing factor. Even though they could not initially pinpoint what caused the relaxation of the endothelium, scientists knew that such a relaxing factor existed and the race was on to identify it. The endothelium is the thin membrane that lines the inside of the heart and blood vessels. The breakthrough came in 1987 when it was shown that endothelium-derived relaxing factor and NO are the same or almost the same thing. Nitric oxide was the agent responsible for relaxing the endothelium. (Ghasemi, 2011)
In 1992, NO was proclaimed as the molecule of the year and in 1999, Furchgott, Ignarro, and Murad were awarded the Nobel Prize in Physiology or Medicine for studies in the NO field. Due to the proven roles played by NO physiologically and pathologically, research on NO was increased rapidly and at the end of the 20th century, the rate of NO publications was approximately 6,000 papers per year, with currently more than 100,000 references invoking NO listed in PubMed.” (Ghasemi, 2011)
In our earlier discussion of nitric oxide as the curing molecule in bacon, we referred to S. J. Haldane who was the first person to demonstrate that the addition of nitrite to haemoglobin (blood protein) produces a nitric oxide (NO)-heme bond, called iron-nitrosyl-hemoglobin (HbFeIINO). He showed that nitrite is further reduced to nitric oxide (NO) in the presence of muscle myoglobin (muscle protein key in supplying oxygen to the muscle) and forms iron-nitrosyl-myoglobin. It is nitrosylated myoglobin that gives cured meat, including bacon and hot dogs, their distinctive red colour and protects the meat from oxidation and spoiling. Discovering that Nitric Oxide (NO) is a key molecule in human physiology should not have been a surprise to meat scientists. There was, an understanding in meat science since the time of Haldane that the nitrate-nitrite-NO pathway was the curing reactions in meat from saltpetre to nitric oxide. It was later decided to use nitrite directly for reasons elucidated in a previous part of this series, Part 2: The Curing Molecule
When we say that the reduction of nitrite to nitric oxide occurs chemically, we refer to the non-enzymatic reduction of nitrite to nitric oxide. Ghasemi (211) gives us the technical details of this. “NO was found to be synthesized from L-arginine by the enzymes known as NO synthase (NOS) (EC 22.214.171.124) in two separate mono-oxygenation steps; first, L-arginine is converted to N-hydroxyarginine in a reaction requiring one O2 and one NADPH and the presence of tetrahydrobiopterin (BH4) and in the second step, by oxidation of N-hydroxyarginine citrulline and NO are formed. At least three NOS enzyme isoforms including neuronal, inducible, and endothelial (eNOS) have been identified and encoded by different genes.”
This non-enzymatic production of Nitric Oxide was suggested in 1997 by Ghafourifar and Richter. They postulated the “existence of mitochondrial NOS and in 1994, Lundberg and colleagues and Benjamin and colleagues demonstrated NOS-independent NO formation. Non-enzymatic NO production by one-electron reduction of nitrite, a blood and tissue NO reservoir, seems to be found everywhere and greatly accelerated under hypoxic conditions or conditions of low oxygen levels in your body tissues. This finding changes the general belief that nitrate and nitrite are waste products of NO.” (Ghasemi, 2011)
I want to refer as an important sidenote at this point to the work of Vanek (2022) which we will look at in much greater detail in a following discussion since they beautifully elucidates the reason for the importance of Nitric Oxide and how it binds to the meat protein we rely on in meat curing, forming the reddish/ pinkish colour of cured meat and giving muscles its characteristic red colour. The important point is that just as nitric oxide is produced through enzymes and non-enzymatic ways to react with myoglobin, in the same way and hugely important to meat curing is that myoglobin has also been shown to have enzymatic functions and is responsible for the decomposition of bioactive nitric oxide to nitrate. The importance of this point can hardly be over-stated! If we are able to convert L-arginine into Nitric Oxide in other ways besides indigenously through NO synthase (the enzymes responsible for oxidising nitrogen in L-Arginine to nitric oxide), and so cure meat, and should we find that this can be done through bacteria, then we still do not strictly speaking have meat curing with no nitrite present as the nitrate will be converted through bacteria in the meat to nitrite and albeit this being present at very low dosages, there will still be nitrite in the meat that we cured.
Allow me to state it again. If we are able to access L-arginine either through bacteria or enzymes directly (as we do in salt-only-long-term-cured-hams) and as a result of this do not start our curing process with nitrite (as is the case with long-term salt-only cured hams) and we are able to claim that we cure meat with no nitrite salts as we are indeed able to do at the present time, then we can not say that we eliminated nitrite from meat curing because there is the likelihood that some of the NO will be converted to nitrate which will be reduced to nitrite again and we are back at the beginning of the quest for nitrite-free curing. Stated a different way, it would seem that curing without nitrite is not possible. This is the heart of the conundrum of people propagating that meat has been cured with no nitrites in that we are dealing with REACTIVE nitrogen species and where you find the one, you are likely to find the others. Our nitrogen species of interest, when we refer to “we will find the one where we find the others” are nitrate, nitrite and nitric oxide, but as we will see further on, these are by no means the only nitrogen species we will encounter in the human muscle and in meat curing alike.
The extent to which what I suggest above is true, we will have to verify through experimentation. The rest of this document is dedicated to answering the following question: why would we want to eliminate a physiologically important species of nitrogen from our diet in any event!? So, on the one hand, is nitrite free curing a realistic goal and secondly, why would we want to do it? Are there other ways to overcome the health concerns associated with cured meats?
Effects of Nitrite in Human physiology.
– Sources of nitrogen for Human Physiology and the Value of Nitrite
The great discovery of the past few decades is that nitrate and nitrite have a fundamentally important role in our physiology and nitrite in particular, namely to act as a reservoir for nitric oxide (NO) which is a physiologically important molecule. Apart from nitric oxide being generated from the amino acid, L-Arginine, nitric oxide is generated through what is referred to as the nitrate-nitrite-Nitric Oxide pathway which is, as we have said before, exactly the same pathway of bacon curing. So, in order for this mechanism to work, we need a direct source of nitrates or nitrites and nature provided this for us in what we eat. The biggest source is vegetables which account for 60%–80% of the daily nitrate intake in a Western diet. As you will see from the table below, they not only supply us with nitrates but with nitrites directly as well. It has been shown that elevations in the blood plasma nitrite levels can occur by increasing the dietary nitrate intake. (Kobayashi, 2015)
Nitrate, nitrite and nitric oxide are closely linked as the difference between them is one oxygen atom. NO3– (nitrate), NO2– (nitrite) and NO (nitric oxide). Nitrate is reduced to nitrite through bacteria and nitrite to nitric oxide through chemical means (enzyme and non-enzyme driven). NO can be oxidized back to nitrite again and nitrite to nitric oxide. Nitric oxide, in the presence of myoglobin, can be converted directly back to nitrate. As a result of this, where one finds nitrate and bacteria such as in the mouth or digestive tract, you will always find nitrite and nitric oxide and where you have nitric oxide, one can find nitrite and nitrate. This is true in meat curing and true in the human body. “In humans and other mammals, about one-quarter of all circulating inorganic nitrate (NO3−), derived from diet or oxidation of endogenous (within the body) nitric oxide (NO), is actively taken up by the salivary glands and excreted in saliva. As a result, salivary nitrate levels are 10–20 times higher than those levels found in our blood. The mechanism behind this massive nitrate accumulation in saliva has remained elusive. The work by Qin et al. reports that the protein sialin can function as an effective nitrate transporter.” (Lundberg, 2012)
With these brief remarks, we are then thrust into the domain of the nitrate-nitrite-NO cycle in the human body. Nitrite is no longer viewed as something to be avoided at all cost, but as a chemical essential for human life and cured meat becomes by far, not the biggest contributor of nitrate and nitrite to our system, but the possibility exists for it to become an important one as we can use the same basic principles that gave us cured meat, reduce the fat and salt and find ways to introduce essential goodness of plant matter and we are confronted with the amazing opportunity to change processed food into a superfood! In this one statement, I seek to address the unfounded negative perception of nitrite, give a clue as to the possible real reason behind the health concerns related to processed meat (fat, salt, phosphates, etc) and give a roadmap for future work by imaginative food scientists in the incorporation of healthy plant matter into the sought after food group, allowing for all the conveniences that make processed-meats a well-loved and very convenient food for our era!
Have a look at the table below which gives the main dietary sources for nitrate and nitrites. Pay close attention to where hot dogs and bacon feature on the list!
Sindelar (2012), as quoted by (Kobayashi, 2015)
Hord (2009) as quoted by (Kobayashi, 2015)
When we ingest nitrates from leafy green vegetables or cured meat, it is absorbed in the upper gastrointestinal tract which comprises the mouth, salivary glands, oesophagus, stomach, and small intestine. The levels in the blood reach the highest level around 30–60 min after the nitrates have been swallowed. Approximately 25% of nitrate absorbed by the body reappears in our mouth through our salivary glands which pump it back into our mouths. Here it is reduced by the bacteria on our tongue from nitrate to nitrite. As it reaches our stomach, a part of the nitrites which we swallow is what we call protonated (adding hydrogen to the nitrite) and nitrous acid is formed which is the form that nitrite takes on when diluted into water (NO2− + H+ → HNO2). This reaction is similar to what happens to nitrite when we dilute it into the curing brine and inject it into meat which is also a more acidic environment like the stomach. Similar to meat curing, the nitrite we ingested now decomposes to form a variety of nitrogen oxides such as Nitric Oxide, the curing molecule, nitrogen dioxides (NO2), and dinitrogen trioxide (N2O3) (2 HNO2 → N2O3 + H2O, N2O3 → NO + NO2). These nitrogen oxides form additional bioactive adducts, such as S-nitrosothiols and N-nitrosamines. S-nitrosothiols sound very intimidating but are not. They are proteins discovered in the 90s and have since been shown to be key in many biochemical processes in our body. Specifically, S-nitrosothiols play a key role in the total system encompassing our heart and blood vessels, for example, the widening of blood vessels as a result of the relaxation of the blood vessel’s muscular walls and preventing thrombosis. N-nitrosamines are known to us by now as formed by the reaction of nitrite with secondary amines which can be cancer-causing.” (Kobayashi, 2015)
The next point requires us to know what gastric mucosa refers to. It is the mucous membrane layer of the stomach, which contains the glands and the gastric pits. Blood flow plays an important role in the protection of normal gastric mucosa and in the protection and healing of damaged mucosa. “Nitric Oxide production in the stomach is greatly enhanced in the presence of micronutrients that naturally occur in plants called dietary polyphenols and vitamin C or ascorbic acid, whereas because of its lower stability and shorter half-life relative to S-nitrosothiols, the released Nitric Oxide in the stomach is thought to locally contribute to increasing the gastric mucosal blood flow and mucous thickness to ensure the normal gastric physiology, and serves as the first-line host defence against harmful bacteria which we swallowed with our food. However, not all the nitrite reacts with H+(escapes the protonation) in the acidic milieu of the stomach and enters the systemic circulation, and then reaches the peripheral organs, including skeletal muscles, where it acts in an endocrine manner (like hormones) to exert NO-like activity. An interesting side note is that because the levels of nitrite in the blood are depends to a large degree on the amount of nitrate in the saliva and its reduction to nitrite, the use of antibacterial mouthwash and frequent spitting of saliva consequently decrease the plasma levels of nitrite.” (Kobayashi, 2015) We just said that Nitric Oxide production in the stomach is greatly enhanced in the presence of micronutrients that naturally occur in plants called dietary polyphenols and vitamin C or ascorbic acid. As we will see later, these substances and in particular vitamin A, C and E plays an important role as “blocking” agents by reacting with the partially digested amino acids called amines, and with secondary amines in particular called N-Nitrosamones denoting a reaction between the amine and nitroso component in nitrite, binding nitrogen and nitrogen (therefore the name, N-Nosotros-amines), blocking the formation of n-nitrosamines. Let me state it again. If we ingest nitrite with vitamins a, c, e, etc., these vitamins react with the secondary amines before nitrite can react with it, therefore blocking nitrosamine formation. This is something to look at on its own and we will not spend much more time on this important point. Here, my goal is to show that nitrite is NOT the harmful cancer-causing entity we believed it was, but turns out to be indispensable for healthy living! We can, therefore, for the moment, suspend the concerns about N-nitrosamine formation but rest assured that we will return to this in great detail! For now, let us continue with our focus on nitrites and the diagram below shows the main way we get nitrates and nitrites into our body.
“The plasma nitrite which reaches peripheral tissues is stored in various organs. Although there have been few reports dealing with the tissue levels of nitrate/nitrite following dietary nitrate supplementation in humans, animal studies show that dietary nitrate certainly increases the tissue levels of nitrate/nitrite following an increase in the plasma levels of nitrate/nitrite, which accordingly exerts therapeutic efficacy for animal models of various disease conditions. Interestingly, while acute dietary nitrate intake increases the plasma levels of nitrite in rodents and humans, chronic dietary nitrate intake does not always increase the plasma and tissue levels of nitrite but increases the tissue levels of nitrate and S-nitrosylated products. Although the mechanism underlying this finding is yet to be clarified, there might be some redox equilibrium of nitrate-nitrite-NO after chronic dietary nitrate intake, resulting in oxidation or reduction of the tissue nitrite to form nitrate or S-nitrosylated species, respectively. On the other hand, animal models chronically fed a diet deficient in nitrate/nitrite exhibit significantly diminished plasma and tissue levels of nitrate/nitrite, resulting in increased ischemia-reperfusion injuries in the heart and liver compared with the animal models fed a normal diet. Ischaemia-Reperfusion injury (IRI) is defined as the paradoxical exacerbation of cellular dysfunction and death, following the restoration of blood flow to previously ischaemic tissues. Ischemia or ischaemia is a restriction in blood supply to any tissues, muscle group, or organ of the body, causing a shortage of oxygen. These results suggest that dietary nitrate intake is important in the maintenance of steady-state tissue levels of nitrate/nitrite for NO-mediated cytoprotection. Cytoprotection is a process by which chemical compounds provide protection to cells against harmful agents. (Kobayashi, 2015) The key point is the importance of nitrate and nitrate in our diets and the possible harmful effect of nutrition deficiency in these compounds.
“Historically, the fact that nitrate and nitrite are present in human saliva has received little attention, because no one could attribute any kind of function to these anions. However, this lack of interest ceased in the 1970s, when researchers formulated a pathophysiological model for gastric cancer based on the accumulation of nitrate in saliva. Commensal bacteria in the mouth reduce parts of the salivary-derived nitrate to nitrite (NO2−), and when swallowed into the acidic stomach, this nitrite yields reactive intermediates that can react with dietary compounds to promote the formation of N-nitrosamines (a versatile class of carcinogens in rodents). With the emergence of this theory, nitrate immediately fell into deep disgrace, and ever since that time, authorities worldwide have put strict regulations on allowable levels of nitrate in our food and drinking water.” (Lundberg, 2012)
In the 1990s, research on nitrate took an unexpected turn when two research groups independently showed that salivary nitrate was a substrate for the formation of NO, and we looked at the development of our understanding of the importance of this molecule in our lives earlier on. It was revealed that NO plays “a key role in virtually every aspect of human physiology, including regulation of cardiovascular function, cellular energetics, immune function, neurotransmission, and more. The newly described alternative means of NO generation from nitrate was fundamentally different from the NO synthase pathway; it did not use arginine as a substrate, and it was independent of NO synthases. After the discovery that nitrate could be a substrate for the formation of a potentially beneficial biological messenger, the interest in nitrate shifted away from only being focused on carcinogenesis, and instead, researchers started to study potential NO-like physiological effects of this anion. From intense research performed during the past 15 y, it is now clear that administration nitrate or nitrite has robust NO-like effects in humans and other mammals. These effects include vasodilation, reduction in blood pressure, protection against experimental ischemia-reperfusion injury, reduction in cellular oxygen consumption, reversal of metabolic syndrome, reduction in oxidative stress, stimulation of mucosal blood flow and mucus formation in the gastrointestinal tract, and more.” We will spend time further on many of these in particular looking at lifestyle diseases.
“Intriguingly, most of these nitrate effects occur at dietary doses easily achievable through a normal diet rich in vegetables. Bioactivation of nitrate requires initial reduction to the more reactive nitrite anion, and this reaction is mainly carried out by commensal bacteria in the oral cavity and to a lesser degree, the tissues by mammalian enzymes. Salivary-derived nitrite is partly reduced to NO in the acidic stomach as described above, but much nitrite also survives gastric passage and enters the systemic circulation, which is evident from the marked nitrite increase in plasma seen after ingestion of nitrate. In blood and tissues, nitrite can undergo additional metabolism to form NO and other bioactive nitrogen oxides, including S-nitrosothiols. A number of enzymes and proteins have been shown to act as nitrite reductases, including deoxygenated haemoglobin, myoglobin, xanthine oxidase, mitochondrial respiratory chain enzymes, and more.” (Lundberg, 2012)
This matter of nitrate-nitrite-Nitric Oxide as the reaction sequence from nitrate in saliva becomes very interesting to us in the meat curing industry for one specific reason. When we surveyed the approach taken by the industry and the US government in particular, we noted in Part 3: Steps to secure the safety of cured meat, of our series that the direct application of nitrite was seen as a way to bypass the first bacteria mediated reduction step of nitrate to nitrite. The reasons given by industry and scientists alike was that it would yield better control in the curing process amongst others, as it relates to the lowest possible dosage of nitrite to effect curing since the dose dependency of the toxicity of nitrites was recognised from very early.
Lundberg (2012) surveyed the work of Qin in identifying sialin as the nitrate transporter to the saliva. This is relevant to curing. Lundberg describes a disorder which leads to ineffective transport of nitrate as follows, “Mutations in the sialin gene cause Salla disease and infantile sialic acid storage disorder, which are serious autosomal recessive lysosomal storage disorders characterized by early physical impairment and mental impairment.”
A fibroblast is a type of cell that contributes to the formation of connective tissue. It secretes collagen proteins that help maintain the structural framework of tissues. “Fibroblasts from patients with infantile sialic acid storage disorder show a lower nitrate transport activity compared with healthy controls. The work by Qin et al. also tested the importance of sialin for nitrate transport in the pig in vivo. Interestingly, adenovirus-dependent expression of a sialin mutant vector (sialinH183R) in the salivary gland decreases NO3− secretion in saliva after ingestion of a nitrate-rich diet compared with control animals.” (Lundberg, 2012)
“Sialin is expressed not only in the salivary glands but also in the brain, heart, lung, kidney, and liver, although seemingly at lower levels. The functional importance of nitrate transport into cells in these tissues would be of interest to study. In this context, it is interesting to note that nitrate metabolism does, indeed, occur in mammalian cells, although to a much lesser degree than in bacteria. The work by Jansson et al. reported on a functional mammalian nitrate reductase in numerous tissues, including liver, kidney, and intestines. Xanthine oxido reductase was identified as the major mammalian nitrate reductase, but the study indicated the presence of other unidentified nitrate reductases as well.” (Lundberg, 2012) The observation that nitrate metabolism occurs in mammalian cells, although to a much lesser degree than in bacteria should not escape our notice. I discussed the matter with a collaborator on key projects, Richard Bosman and we speculated that the reason for the curing in long-term salt-only-dry-cured hams probably has more to do with the relaxing of the muscles as a result of early cell breakdown and the accompanying invasion of bacteria able to oxidize L-arginine than with the endogenous oxidants in the meat. This fact possibly further points to a symbiotic evolution of humans with oral cavity bacteria positioned to fulfil this vital role of reducing nitrate to the more reactive nitrite.
“The work by Qin et al. proposes that sialin functions as the major NO3− uptake system in salivary gland cells; however, a remaining question is how this nitrate is further transported to saliva through the apical portion of the cells. Sialin seems to be a versatile anion transporter that also mediates H+-dependent transport of NO2−, aspartate, and glutamate. Previously, antagonism between nitrate, perchlorate, iodine, and thiocyanate for secretion in human saliva was shown, but in the work by Qin et al., these anions are not studied. It will be of interest to study if sialin also transports these anions. Definitive evidence for a functional role of sialin in nitrate transport and systemic nitrite/NO homeostasis in humans is lacking, but with the identification of this protein as an important nitrate transporter, it now seems possible to study this area. One approach could be to study the nitrate–nitrite–NO pathway in genetically engineered mice or perhaps, patients with Salla disease. Are salivary and plasma levels of nitrate/nitrite different in these patients? Do these animals or the patients exhibit any signs of systemic NO deficiency, including increased blood pressure, altered blood flow responses, different cellular energetics, or others? In the case that NO homeostasis is disturbed in Salla disease, would the patients benefit from substitution with nitrite?” (Lundberg, 2012)
This is the relevant question. Look at the possible suggestions. Is it possible to bypass nitrate and the bacterial reduction to nitrite and instead, would a solution be to administer nitrite directly as happens when we ingest nitrate which is transported to the saliva glands and in the mouth, are converted to nitrite, which, in the mouth and in the reducing environment in the stomach is changed to the physiologically vital nitric oxide? Lundberg (2012) puts his finger on the issue when he asks, “By giving nitrite instead of nitrate, one could bypass the initial nitrate transport step that might be disturbed in these patients, and NO and other bioactive nitrogen oxides would form directly from nitrite in blood and tissues.” He points to the fact that this therapeutic approach “was recently successfully tested in another genetic disorder involving a disturbed NO homeostasis.” Homeostasis refers to a self-regulating process by which biological systems maintain stability while adjusting to changing external conditions. “Another approach could be to study the proposed negative consequences of nitrate transport. If salivary nitrate transport promotes nitrosamine formation, which has been believed for a long time, are nitrosamine levels and occurrence of gastric malignancies lower in subjects lacking the transporter?” (Lundberg, 2012)
Huizing reports by 2021 that “plasma-membrane nitrate transport in salivary gland acinar cells, remains enigmatic.” (Huizing, 2021) Our hiatus into this question has, however, not been without reward.
- We have seen the widespread distribution of nitrate to physiologically vital sites in the body;
- We glimpsed at the key role of nitrite in the blood plasma, mainly derived from ingested nitrate and nitrates.
- We see how other scientists in other fields of study came to the same conclusion as food scientists in the early 1900 namely that a direct application of nitrite, bypassing the time and bacteria dependant reduction step of nitrate has beneficial consequences.
In the discussion about possible negative effects of nitrite, one very important point to remember is that our overall natural design favours an adequate intake of nitrites. This can be seen by its presence in our blood. Here, nitrite is reduced to nitric oxide.
Gladwin (2008) that “recently, multiple physiologic studies have surprisingly revealed that nitrite represents a biologic reservoir of NO that can regulate hypoxic vasodilation, cellular respiration, and signalling.” They summarise that “studies suggest a vital role for deoxyhemoglobin- and deoxymyoglobin-dependent nitrite reduction. Biophysical and chemical analysis of the nitrite-deoxyhemoglobin reaction has revealed unexpected chemistries between nitrite and deoxyhemoglobin that may contribute to and facilitate hypoxic NO generation and signalling. The first is that haemoglobin is an allosterically regulated nitrite reductase, such that oxygen binding increases the rate of nitrite conversion to NO, a process termed R-state catalysis. The second chemical property is oxidative denitrosylation, a process by which the NO formed in the deoxyhemoglobin-nitrite reaction that binds to other deoxyhemes can be released due to heme oxidation, releasing free NO. Third, the reaction undergoes a nitrite reductase/anhydrase redox cycle that catalyzes the anaerobic conversion of 2 molecules of nitrite into dinitrogen trioxide (N2O3), an uncharged molecule that may be exported from the erythrocyte. We will review these reactions in the biologic framework of hypoxic signalling in blood and the heart.”
It is interesting that nitric oxide produced in the endothelium is oxidised to nitrite. In this instance, one could say that it “bypasses” the intestinal section where it could react with amino acids to form n-nitrosamines which some of them can cause cancer. Rassaf (2014) states that Nitric Oxide is produced in the body from the amino-acid L-arginine by the NO-synthases (NOSs). Three different NOSs exist: the endothelial NOS (eNOS, NOS III), the inducible NOS (iNOS, NOS II) and the neuronal NOS (nNOS, NOS I). This may be one way that the body uses to “manage” the possible harmful effects of nitrite but there are others as we have already eluded to and will look at in greater detail further on, namely ways to “block” nitrite through ingested vitamins. Still, there is another important mechanism which we will discuss in the future when we focus on n-nitrosamines and ways to mediate its possible harmful effect. Note that making it mandatory to include vitamin C in cured meats has been a strategy employed by the industry and regulated by governments from very early on. I will say a bit more about this at the end of this article.
Let’s return to the endothelial. The endothelial is the largest organ system in the body. I repeat the definition as I realise that these concepts may be new to many of the readers and repetition aids learning! It refers to a single layer of cells, called endothelial cells which lines the inside of all blood vessels (arteries, veins and capillaries). Inductable NOS is expressed after cell activation only and then produces NO for comparatively long periods of time (hours to days) in response to autoimmune and chronically inflammatory diseases in humans and neurodegenerative diseases and heart infarction, during tumour development, after transplantation, during prostheses failure and myositis. (Kröncke, 1998) Neuronal or nNOS relates to the brain. “Brain nNOS exists in particulate and soluble forms and the differential subcellular localization of nNOS may contribute to its diverse functions and has been implicated in modulating physiological functions such as learning, memory, and neurogenesis, as well as being involved in a number of human diseases.” (Zhou, 2009)
Let’s return to Gladwin (2008) who now describes a fascinating cycle of Nitric Oxide in the blood which relies on its conversion to nitrite. As we have seen above, Nitric Oxide is produced in endothelium and then diffuses to adjacent smooth muscle to activate soluble guanylyl cyclase that produces cGMP, and ultimately produces smooth muscle relaxation. Nitric oxide is subject to rapid inactivation reactions with haemoglobin that greatly limit its lifetime in blood, however recent studies suggest that NO formed from endothelial NO synthases is also oxidized by oxygen or plasma ceruloplasmin to form nitrite. Nitrite transport in blood provides an endocrine (from glands) form of NO that is shuttled from the lungs to the periphery while limiting the exposure of authentic NO to the scavenging red cell environment. Then during the rapid haemoglobin deoxygenation from artery to vein, the nitrite is reduced back to NO. Such a cycle conserves NO in the one-electron oxidation state. In this model, the nitrite pool represents the “live payload,” only one electron away from NO.”
If the body then generates enough Nitric Oxide, is there a requirement for additional dietary intake of nitrate or nitrite? “It has been suggested that the nitrate-nitrite-NO pathway serves as a backup system to ensure sufficient NO generation under hypoxic conditions when NOS may be malfunctioning.” (Ghasemi, 2011)
“It has been shown that 3-day dietary supplementation with sodium nitrate (0.1 mmol/kg/day) could reduce significantly diastolic blood pressure in non-smoking healthy volunteers. Recently, a large cohort study of 52,693 patients from 14 countries with acute coronary syndrome, of whom 20% were on chronic nitrate, demonstrated that chronic nitrate therapy (medication routinely taken at home and started at least 7 days prior to index event) was associated with reduced severity of myocardial injury in response to acute coronary events. The result showed that the proportion of these subjects with ST-segment elevation myocardial infarction was 41% in nitrate-naïve patients compared to only 18% in nitrate users and conversely a higher percent of nitrate users (82%) presented with non-ST-segment elevation acute coronary syndrome compared to 59% in nitrate-naïve patients.” (Ghasemi, 2011)
“Increasing nitrate or nitrate dietary intake provides significant cardioprotection against ischemia-reperfusion (I/R) injury in mice and it has been proposed that nitrite-/nitrate-rich foods may provide protection against cardiovascular conditions characterized by ischemia. It has been suggested that the nitrate-nitrite-NO pathway serves as a backup system to ensure sufficient NO generation under hypoxic conditions when NOS may be malfunctioning.” (Ghasemi, 2011)
“Abundant consumption of fruits and vegetables, especially green leafy vegetables, is associated with lower risk of cardiovascular disease. It has been proposed that inorganic nitrate, which is found in vegetables with a high concentrations, i.e. >2000-3000 mg/nitrate/kg, is the major factor in contributing to the positive health effects of vegetables via bioconversion to nitrite, NO, and nitroso-compounds, NOx intake now being considered as a dietary parameter for assessing cardiovascular risk.” (Ghasemi, 2011)
“Any intervention that increases blood and tissue concentration of nitrite may provide cardioprotection against I/R injury because it serves as a NOS-independent source of NO and reacts with thiols to form S-nitrosothiols. Nitrate-nitrite-NO pathway can be boosted by exogenous administration of nitrate or nitrite and this may have important therapeutic as well as nutritional implications. However, additional studies are required to clarify the protective roles of nitrate, considering the medical status of subjects, concomitant use of inhibitors of endogenous nitrosation (e.g. vitamin C and E), or foods containing high levels of nitrosatable precursors (e.g. fish). Some individuals, including those with high blood pressure and atherosclerosis, may benefit from increased nitrate while those with oesophagal dysplasia should avoid foods with high concentration of nitrate.” (Ghasemi, 2011)
The value of nitrite in the human body, however, goes far beyond only a reservoir of Nitric Oxide. We have eluded time and time again to many of the benefits and we now drill down on some of the different benefits or tahre, its role in resolving some of the negative lifestyle diseases prevalent in our modern era. “Nitrite-induced transnitrosylation in organs might be an alternative in vivo nitrite signalling for the mammalian biology including protection of protein thiols from irreversible oxidation, transcriptional modulation, and posttranslational regulation of most classes of proteins present in all cells, and also that changes in plasma nitrite levels even within the physiological ranges (e.g., postprandial and fasting) can affect tissue levels of S-nitrosothiol and subsequent cellular biology.” (Kobayashi, 2015)
-> Protective Effects of Dietary Nitrate/Nitrite on Lifestyle-Related Diseases
Kobayashi (2015) reviewed nitrites’ protective effect on lifestyle-related diseases. They write: “Lifestyle-related disease is a chronic disease characterized by oxidative and proinflammatory state with reduced NO bioavailability. The cellular redox balance in these patients shifts toward a more oxidizing state which affects a number of protein functions at the transcriptional and posttranslational levels, consequently disrupting the cellular homeostasis. However, increased NO bioavailability can improve the intracellular redox environment by S-nitrosylation-mediated modulation of most classes of proteins present in all cells. Recently, accumulating evidence has suggested that dietary nitrate/nitrite improves the features of lifestyle-related diseases by enhancing NO availability, and thus provides potential options for prevention and therapy for these patients. Based on the recent evidence, the beneficial effects of a diet rich in these components are discussed below, focusing on insulin resistance, hypertension, cardiac ischemia/reperfusion injury, chronic obstructive pulmonary disease (COPD), cancer, and osteoporosis.”
“The insulin receptor shares a signalling pathway with the activation of endothelial NOS (eNOS) to regulate the postprandial blood flow and efficient nutrient disposition to peripheral tissues. Therefore, insulin resistance is always associated with impaired NO availability, suggesting that a reciprocal relationship exists between insulin activation and endothelial function. Insulin resistance is improved by NO at various levels including insulin secretion, mitochondrial function, modulation of inflammation, insulin signalling and glucose uptake. For example, insulin-stimulated NO production has physiological consequences resulting in capillary recruitment and increased blood flow in skeletal muscle, leading to efficient glucose disposal.” (Kobayashi, 2015)
However, the most important mechanism to improve insulin resistance might be at the post-receptor level of insulin signalling. In diabetic states, increased adiposity releases free fatty acids and produces excessive reactive oxygen species (ROS) through a toll-like receptor 4 (TLR4)-mediated mechanism, which activates a number of kinases and phosphatases, and then disrupts the balance of protein phosphorylation/dephosphorylation associated with insulin signalling. The mechanisms underlying the NO-mediated beneficial effects on insulin resistance are as follows: First, NO suppresses the TLR4-mediated inflammation and ROS production by inactivating IkB kinase-β/nuclear factor-κB (IκκB/NF-κβ), the main trigger for the induction of a number of proinflammatory cytokines. Second, Wang et al., indicated that NO mediates the S-nitrosylation of protein-tyrosine phosphatase 1B (PTPB1) and enhances the effects of insulin. Because PTPB1 dephosphorylates the insulin receptor and its substrates, attenuating the insulin effect, its phosphatase activity tends to be suppressed by eNOS-mediated S-nitrosylation. In contrast, when the vascular eNOS activity is impaired, PTPB1 suppresses the downstream signalling to PI3K/Akt, leading to insulin resistance. Therefore, NO might act as a key regulatory mediator for the downstream signalling linking glucose transporter 4 (GLUT4) translocation and glucose uptake. Third, Jiang recently reported that NO-dependent nitrosylation of GLUT4 facilitates GLUT4 translocation to the membrane for glucose uptake, and improves insulin resistance. Fourth, excess nutrients also overproduce superoxide in the mitochondrial respiratory chain, leading to the subsequent formation of ROS. NO can inhibit mitochondrial ROS production through the S-nitrosylation of mitochondrial respiratory chain complex 1 enzyme and by improving the efficiency of oxidative phosphorylation in the mitochondria.” (Kobayashi, 2015)
“Indeed, the therapeutic potential of dietary nitrate/nitrite has been supported by recent studies demonstrating the improvements of insulin resistance in humans and animals as a result of its enhancing the NO availability in plasma and tissues. As mentioned above, insulin resistance always accompanies metabolic and endothelial dysfunction, which leads to hypertension and atherosclerosis. Enhancement of the availability of NO might therefore be a promising strategy for the prevention and treatment of patients with not only insulin resistance but also endothelial dysfunction.” (Kobayashi, 2015)
-> Cardiac Ischemia/Reperfusion Injury
“During heart ischemia, ATP is progressively depleted in cardiac muscle cells, which impairs ion pumps, leads to the accumulation of calcium ions, and consequently damages the cell membrane stability. On reperfusion, the cardiac muscle cells are further injured, because in the mitochondria, ROS are produced in large quantities due to massive electron leaks and the formation of superoxide with the resupplied oxygen, which denatures cytosolic enzymes and destroys cell membranes by lipid peroxidation. ROS-mediated dysfunction of the sarcoplasmic reticulum also induces massive intracellular calcium overload, leading to the opening of the mitochondrial permeability transition pore and causing cell apoptosis or necrosis, depending on the intracellular ATP levels. The availability of vascular NO would thus be expected to be impaired due to the reduced NOS activity in ischemia and subsequent consumption by superoxide during reperfusion, resulting in severe ischemia/reperfusion injury.” (Kobayashi, 2015)
“Nitrite, nitrate, and NO-related compounds (e.g., S-nitrosothiols) are constitutively present in blood and tissues. The nitrite level in cardiac tissue is a couple of times higher than that in plasma due to an unknown form of active transport from blood to tissues or due to the oxidation of endogenously generated-NO to nitrite by ceruloplasmin, and serves as a significant extravascular pool for NO during tissue hypoxia. Carlström et al., showed that dietary nitrate increased the tissue levels of nitrite and S-nitrosothiols in the heart, and attenuated oxidative stress and prevented cardiac injury in Sprague-Dawley rats subjected to unilateral nephrectomy and a high-salt diet. Shiva et al., recently showed that the nitrite stored in the heart and liver via systemic and oral routes augmented the tolerance to ischemia/reperfusion injury in the mouse heart and liver.” (Kobayashi, 2015)
“Although the genetic overexpression of eNOS in mice attenuates myocardial infarction, in general, the protective effects of NO on cardiac ischemia/reperfusion injury depend on the local stock of nitrite and its subsequent reduction to NO at the critical moment when NOS activity is lacking under hypoxic conditions. Indeed, the tissue levels of S-nitrosothiols (NO-mediated signalling molecules) are enhanced through the nitrite reduction due to NOS inhibition, hypoxia, and acidosis, suggesting that the tissue nitrite stores can be regarded as a backup and on-demand NO donor. There are a number of factors that have been demonstrated to reduce nitrite in the tissues, including deoxyhemoglobin, deoxymyoglobin, xanthine oxidoreductase, heme-based enzymes in the mitochondria and acidosis during ischemia. In patients with coronary heart disease, the different consequences of myocardial infarction may depend on the patient’s daily intake of nitrate/nitrite. Indeed, Bryan et al., showed that dietary nitrite (50 mg/L) or nitrate (1 g/L) supplementation in drinking water for seven days maintained higher steady-state levels of nitrite and nitroso compounds, as well as nitrosyl-heme, in mouse cardiac muscle, and these mice exhibited a smaller cardiac infarct size after ischemia/reperfusion injury compared with control mice fed a diet deficient in nitrate/nitrite for seven days. These findings suggest that this protective nitrate/nitrite may be derived at least in part from dietary sources.” (Kobayashi, 2015)
“Shiva et al., demonstrated that the cytoprotective effects of nitrite on ischemia/reperfusion injury are mediated by post-translational S-nitrosylation of complex 1 in the mitochondrial respiratory chain, which consequently inhibits the overall mitochondrial ROS formation and apoptotic events. Another possible cytoprotective effect of nitrite may be mediated by the effects of S-nitrosylation on the intracellular Ca2+ handling, which decreases Ca2+ entry by inhibiting L-type Ca2+ channels and increasing the sarcoendoplasmic reticulum (SR) Ca2+ uptake by activating SR Ca2+ transport ATPase (SERCA2a) . These effects will lead to an attenuation of the increase in cytosolic Ca2+ during ischemia and Ca2+ overload during reperfusion.” (Kobayashi, 2015)
“Intriguingly, recent large-scale epidemiological studies reported the preventive effects of antioxidant supplementations including vitamins E, C, and beta carotene rich in fruits and vegetables on cardiovascular disease, whereas no beneficial effects were shown in other studies, and in some cases, a decrease in cardiovascular protection with these supplementations was observed. On the other hand, a number of epidemiological studies have shown the preventive effects of fruits and vegetables on coronary heart disease. It should be noted that the consumption of an appropriate amount of fruits and vegetables, which might contain balanced doses of nitrate/nitrite and vitamins, might be more effective with regard to health maintenance and improvement than antioxidant supplementation alone.” (Kobayashi, 2015) It is this finding in particular that gives direction to my work with two collaborators Richard Bosman and Dr Jess Goble. Whether we will succeed in our quest, time will tell but we have some impressive early breakthoughs and with solid support of scientists, industry professionals and inventors of new technology which has the potential to unluck the application of these fruits and vegetables to meat, we are hopeful and extremely motivated!
-> Chronic Obstructive Pulmonary Disease (COPD)
“COPD is considered to be a lifestyle-related disease because long-term tobacco smoking and subsequent chronic bronchitis are causally associated with this disease. Varraso et al., recently reported the importance of a healthy diet in multi-interventional programs to prevent COPD. They showed that high intake of whole grains, polyunsaturated fatty acids, nuts, and long chain omega-3 fats, and low intake of red/processed meats, refined grains and sugar-sweetened drinks, were associated with a lower risk of COPD in both women and men.” (Kobayashi, 2015)
“Because cured meats such as bacon, sausage and ham contain high doses of nitrite for preservation, antimicrobial and colour fixation, epidemiological studies have demonstrated that the consumption of cured meats is positively linked to the risk of newly diagnosed COPD. Nitrite generates reactive nitrogen species, which may cause nitrosative damage to the lungs, eventually leading to structural changes like emphysema. This is supported by an animal study in which rats chronically exposed to 2000 and 3000 mg/L of sodium nitrite in their drinking water for two years showed distinct lung emphysema. However, the dose of nitrite used in that study was 250–350 mg/kg/day, which was too high to compare with those achieved in standard human diets.
In fact, cured meats have been reported to generally comprise only 4.8% of the daily nitrite intake, and 93% of the total ingestion of nitrite is derived from saliva, suggesting that cured meats provide minimal contributions to the human intake of nitrite, even if they are frequently consumed. In addition, the recent nitrite levels in processed meats have been approximately 80% lower than those in the mid-1970s in the US. Therefore, discussions encompassing all ingested sources of nitrite should consider whether or not the nitrite derived only from the consumption of cured meats might be responsible for the development of COPD.” (Kobayashi, 2015)
“On the other hand, a number of epidemiological studies have shown the beneficial effects of n-3 fatty acids, vitamins, fruits and vegetables on lung functions and the risk of COPD. Although it may be difficult to isolate the specific effects of these dietary nutrients, as discussed above, the nitrate and nitrite derived from vegetables and fruits are reduced to NO, which is followed by the formation of S-nitrosothiols, rather than the formation of nitrosamines especially in the presence of reducing agents such as vitamin C and E in the stomach. It has been shown that high dietary nitrate intake does not cause the expected elevation of the gastric nitrite concentrations or appreciable changes in the serum nitrite concentrations.” (Kobayashi, 2015) As I stated previously, these findings do not cause the industry to sit back and proclaim, “you see, consumption of cured meat is safe” even though the validation is encouraging – in the case of me and my collaborators it energises us to do even better and work to turn cured meat into a superfood.
“As mentioned above, different from the effects of the direct elevation of nitrite concentration in the plasma, the entero-salivary route of dietary nitrate/nitrite might enhance the availability of NO through the formation of S-nitrosothiols and its transnitrosylation to the other thiol residues of proteins, suggesting that, depending on the tissues and organs, separate metabolic pathways might exist for NO availability in this entero-salivary route. Consistent with this idea, Larsen et al., recently demonstrated that acute intravenous infusion of nitrite enhanced the plasma levels of nitrite, whereas it did not affect the oxygen consumption (VO2) or the resting metabolic rate (RMR) in humans. Instead, dietary nitrate significantly reduced the VO2 and RMR by improving the mitochondrial respiratory chain function and enhancing efficient O2 consumption, suggesting that rather than direct nitrite infusion to enhance the plasma nitrite levels, biologically active nitrogen oxide (including the S-nitrosothiols produced in the stomach) might be an important molecule for the transfer of biological NO activity for cardiopulmonary function . Because COPD is a state of protein-energy malnutrition due to an increased resting metabolic rate and VO2, the effects of dietary nitrate on the reduction of the RMR and VO2 might be advantageous for patients with COPD.” (Kobayashi, 2015)
“Whether the role of NO in COPD is protective or pathogenic depends on the origin and concentration range of NO. NO activity derived from dietary nitrate and constitutive NOS might be protective against COPD largely through the S-nitrosothiol-mediated mechanism including inhibition of the noncholinergic nonadrenergic nerve activity, bronchial smooth muscle relaxation, reduction of airway hyperresponsiveness, downregulation of the proinflammatory activity of T lymphocytes, and antimicrobial defence. However, the deleterious effects of NO on the development of COPD might be derived from iNOS-mediated pro-inflammatory signalling, which is consequently (not causally) reflected by the huge amount of NO in the exhaled air of patients with COPD.” (Kobayashi, 2015)
“Recent human studies have demonstrated that dietary nitrate (beetroot juice containing approximately 200–400 mg of nitrate) improved the exercise performance and reduced blood pressure in COPD patients. However, large-scale epidemiological evidence of the impact of nitrate is still lacking.” (Kobayashi, 2015)
-> Lowering Blood Pressure
An obvious benefit of nitrite is its role as a reservoir of Nitric Oxide which is a key molecule which blood pressure. The blood pressure-lowering and performance-enhancing effects of nitrites have been known for many years. (Keller, 2017) This is due to the fact that the nitrite anion (NO–2) acts as an endogenous nitric oxide source. (Keszler, 2008) Nitrite is reduced to nitric oxide (NO). “One major mechanism of nitrite reduction is the direct reaction between this anion and the ferrous heme group of deoxygenated haemoglobin.” The oxidation reaction of nitrite with oxyhemoglobin (oxyHb) which is formed by the combination of haemoglobin with oxygen, is also well established and generates nitrate and methemoglobin (metHb). (Keszler, 2008)
“Increased consumption of fruits and vegetables is associated with a reduction of the risk of cardiovascular disease. The DASH studies recommended the consumption of diets rich in vegetables and low-fat dairy products to lower blood pressure, and these effects are thought to be attributable to the high calcium, potassium, polyphenols and fiber and low sodium content in these food items. However, vegetable diets containing high nitrate levels increase the plasma levels of nitrate and nitrite, which are the physiological substrates for NO production. Accumulating evidence has recently indicated that the nitrate/nitrite content of the fruits and vegetables could contribute to their cardiovascular health benefits in animals and humans.” (Kobayashi, 2015)
“A number of publications have demonstrated that dietary nitrate reduces blood pressure in humans. Larsen et al., reported that the diastolic blood pressure in healthy volunteers was reduced by dietary sodium nitrate (at a dose of 0.1 mmol/kg body weight per day) corresponding to the amount normally found in 150 to 250 g of a nitrate-rich vegetable, such as spinach, beetroot, or lettuce. Webb et al., studied the blood pressure and flow-mediated dilation of healthy volunteers, and showed that the vasoprotective effects of dietary nitrate (a single dose of 500 mL of beetroot juice containing 45.0 ± 2.6 mmol/L nitrate), were attributable to the activity of nitrite converted from the ingested nitrate . Kapil et al., also showed a similar finding that consuming 250 mL of beetroot juice (5.5 mmol nitrate) enhanced the plasma levels of nitrite and cGMP with a consequent decrease in blood pressure in healthy volunteers, indicating that there was soluble guanylate cyclase-cGMP-mediated vasodilation following a conversion of the nitrite to bioactive NO. They later presented the effects of dietary nitrate on hypertension, and showed the first evidence that daily dietary nitrate supplementation (250 mL of beetroot juice daily) for four weeks reduced the blood pressure, with improvements in the endothelial function and arterial stiffness in patients with hypertension. Because arterial vascular remodelling is the major histological finding associated with ageing, these vascular structural changes represent vascular wall fibrosis with increased collagen deposits and reduced elastin fibers, which result in arterial stiffening and subsequent hypertension in elderly patients. Sindler et al., recently demonstrated that dietary nitrite (50 mg/L in drinking water) was effective in the treatment of vascular ageing in mice, which was evidenced by a reduction of aortic pulse wave velocity and normalization of NO-mediated endothelium-dependent dilation. They showed that these improvements were mediated by reduction of oxidative stress and inflammation, which were linked to mitochondrial biogenesis and health as a result of increased dietary nitrite. These beneficial effects were also evident with dietary nitrate in their study, suggesting that dietary nitrate/nitrite may be useful for the prevention and treatment of chronic age-associated hypertension.” (Kobayashi, 2015)
“In addition, hypertension is also a major cause of ischemic heart and cardiac muscle remodelling, which lead to congestive heart failure. Bhushan et al., reported that dietary nitrite supplementation in drinking water (50 mg/L sodium nitrite, for nine weeks) increased the cardiac nitrite, nitrosothiol, and cGMP levels, which improved the left ventricular function during heart failure in mice with hypertension produced by transverse aortic constriction. They also showed that dietary nitrite improved the cardiac fibrosis associated with pressure-overloaded left ventricular hypertrophy through NO-mediated cytoprotective signalling. Although a number of studies on the acute effects of dietary nitrate have been conducted using animal models and healthy humans, more evidence in patients with hypertension, as well as additional studies on the long-term effects of dietary nitrate, will be needed in the future.” (Kobayashi, 2015)
“In the stomach, swallowed nitrite is decomposed to form a variety of nitrogen compounds, including N-nitrosoamines. In the 1950s, Magree et al., first reported that N-nitrosodimethylamine caused malignant primary hepatic tumours in rats. After this report, a number of studies followed in relation to the carcinogenic effects of N-nitroso compounds in animal models. In particular, the dietary intake of red and cured meats was found to be associated with an increased risk of certain types of cancer due to the relatively large amounts of nitrite added. However, the methodological aspects have been challenged concerning the high dose of nitrosatable amines, and the physiological difference between animals and humans.” (Kobayashi, 2015)
“In the stomach, the nitrosonium ion (NO+) derived from nitrite can bind to thiol compounds (R-SH) and amines (especially secondary amines: R1-NH-R2), forming S-nitrosothiol and N-nitrosamine, respectively. However, while N-nitrosamine formation occurs even at neutral or basic pH, S-nitrosothiol formation tends to occur only under acidic conditions. In addition, this reaction kinetically occurs much more easily than N-nitrosamine formation, particularly in the presence of vitamins C and E and polyphenols, which are highly present in fruits and vegetables, which also eliminate potent nitrosating agents such as the N2O3 formed from nitrite by decomposing them to NO. This might partly explain why patients with achlorhydria and non-vegetarians eating large amounts of cured meats are at risk of developing gastric cancer.” (Kobayashi, 2015) Epidemiological studies mostly indicate that abundant consumption of vegetables reduce the risk of cancer (Block et al., 1992; Terry et al., 2001). (Rassaf, 2014)
“However, this idea appears to be inconsistent with the belief that dietary nitrite is a major cause of cancer. This is because, according to the average nitrate/nitrite intake of adults in the US, most of the daily nitrate intake (around 90%) comes from vegetables, and the nitrite intake is primarily derived from recycled nitrate in the saliva (5.2–8.6 mg/day nitrite), with very little coming from cured meats (0.05–0.6 mg/day nitrite in 50g/day cured meats) and other dietary sources (0–0.7 mg/day nitrite) , suggesting that the entero-salivary route may be the more important source of nitrosamine exposure than exogenous intake including cured meats, that is, spitting out saliva all day long might prevent cancer development more effectively than cutting cured meats. However, recent experimental and epidemiological studies could not demonstrate a positive relationship between nitrate consumption and the risk of cancer.” (Kobayashi, 2015) These epidemiologic studies include Van Loon et al., 1998; Pannala et al., 2003; Hord et al., 2009; Tang et al., 2011. “The Joint Food and Agriculture Organization/World Health Organization Expert Committee on Food Additives concluded in 2008 that there was no evidence that nitrate was carcinogenic in humans. Consistent with this, recent studies have found no link between dietary nitrate and cancer.” (Kobayashi, 2015)
“Bradbury et al., reported a large-scale study (>500,000 participants) of the associations between fruit, vegetable, or fiber consumption and the risk of cancer at 14 different sites. They showed that there was an inverse association between fruit intake and the risk of upper gastrointestinal tract and lung cancer, as well as an inverse association between fiber intake and liver cancer. The dietary intake of vegetables, as well as fruits and fiber, was inversely associated with the risk of colorectal cancer, suggesting that there is little evidence that vegetable intake is associated with the risk of any of the individual cancer sites reviewed.” (Kobayashi, 2015)
“However, chronic inflammation, including inflammatory bowel disease and Helicobacter pylori-induced gastritis induce inducible NOS (iNOS) and generate large quantities of NO, forming nitrosating and oxidant species such as N2O3 and peroxynitrite, which might cause mutagenesis through deamination, nitration of DNA, or inhibition of the DNA repair system. Depending on the sites and amounts of NO generation, NO might represent a double-edged sword in the sense that it confers both protective and deleterious effects on cancer development.” (Kobayashi, 2015)
“Meta-analyses of primary and secondary cancer prevention trials of dietary antioxidant supplements, such as beta carotene, vitamins A, C, and E, showed a lack of efficacy, and on the contrary, an increased risk of mortality. Although the general role of NO in carcinogenesis is complicated, and many unknown mechanisms remain to be resolved, the dietary nitrate/nitrite (at least that obtained from plant-based foods such as fruits and vegetables) has obvious inhibitory effects on cancer risk by playing some synergistic role with other nutrients in these foods.” (Kobayashi, 2015) It is again findings like these that give direction to our product developments.
“Lifestyle habits, such as smoking, alcohol intake, little or no exercise, and an inadequate amount of calcium intake all influence the calcium-vitamin D metabolism and bone mineral density, in some cases leading to osteoporosis, particularly in postmenopausal women. The implications of NOS-mediated NO in the regulation of bone cell function have been well described in a number of publications. For example, iNOS-induced NO production following stimulation with proinflammatory cytokines, such as interleukin 1 (IL-1) and tumor necrosis factor-α (TNF-α), inhibits bone resorption and formation, resulting in osteoporosis in patients with inflammatory diseases such as rheumatoid arthritis. On the other hand, eNOS, a constitutive NO synthase, plays an important role in regulating osteoblast activity and bone formation, because eNOS knockout mice exhibit osteoporosis due to defective bone formation, and eNOS gene polymorphisms were reported to be causally linked to osteoporosis in postmenopausal women.” (Kobayashi, 2015)
“In addition, Wimalawansa et al., showed that some of the beneficial effects of estrogen on bone metabolism are mediated through a NO-cGMP-mediated pathway, suggesting that NO donor therapy might provide a promising alternative to estrogen therapy. In this context, it has been shown that organic nitrate NO donors, such as glycerol trinitrate, isosorbide dinitrate and mononitrate all have beneficial effects on experimental and clinical osteoporosis, and a number of epidemiological studies also indicated that a high fruit and vegetable intake appears to have a protective effect against osteoporosis in men and pre- and postmenopausal women. However, few studies have been conducted to evaluate the detailed mechanism by which inorganic nitrate/nitrite prevents osteoporosis at the molecular level, and thus further basic research will be needed for this purpose.” (Kobayashi, 2015)
-> Methemoglobinemia (MetHb)
A negative effect of nitrite in the body relates to its link with methemoglobinemia. It is historically this link which contributed to cast nitrite in a negative light and day plays a dominant role in establishing what the WHO regards as safe levels of ingested nitrites.
“Methemoglobinemia (MetHb) is a blood disorder which the US National Institute of Health defines as occurring when “an abnormal amount of methemoglobin is produced.” They explain that “hemoglobin is the protein in red blood cells (RBCs) that carries and distributes oxygen to the body. Methemoglobin is a form of hemoglobin. Inherited (congenital) methemoglobin occurs when the disorder “is passed down through families.” Our interest is in what is referred to as acquired MetHb which is “more common than inherited forms and occurs in some people after they are exposed to certain chemicals and medicines.” One such chemical is nitrites. (National Libary of medecine) “Elevated levels of nitrite in the blood can trigger the oxidation of hemoglobin, leading to methemoglobinemia.” Keszler (2008) suggests a simplified model of the kinetics involved where the end products of the reaction are methemoglobin (metHb) and nitrate.
The “World Health Organization (WHO) used data based on the risk of methemoglobinemia to set an acceptable daily intake (ADI) for nitrate of 3.7 mg/kg body weight per day, equivalent to 222 mg nitrate per day for a 60-kg adult, and nitrite of 0.07 mg/kg body weight per day, equivalent to 4.2 mg nitrite per day for a 60-kg adult. (Keller, 2017)
The upper limit represented by the WHO ADI corresponds to the concentration of dietary nitrate that lowers blood pressure in normotensive and hypertensive adults. (Keller, 2017)
Very high concentrations of nitrate in drinking water may cause methemoglobinemia, particularly in infants (blue baby syndrome). “In the 1940s, Comly first reported cases of cyanotic infants who received formula prepared with well water containing a high nitrate content. Based on the subsequent analyses of the infantile cases of methemoglobinemia, the US Environmental Protection Agency (EPA) set a Maximum Contaminant Level (MCL) for nitrate of 44 mg/L (equal to 10 mg/L nitrogen in nitrate). However, it is now thought that methemoglobinemia per se was not caused by nitrate itself, but by faecal bacteria that infected infants and produced NO in their gut. A recent report by Avery has argued that it is unlikely that nitrate causes methemoglobinemia without bacterial contamination, and also that the 40–50 mg/L limit on nitrate in drinking water is not necessary.” (Kobayashi, 2015)
However, there are now legal limits to the concentrations of nitrate and nitrite in both food and drinking water. The WHO showed that the Acceptable Daily Intake for humans (ADI) for nitrate and nitrite were 3.7 and 0.07 mg/kg body weight/day, respectively, which were based on the calculations from the doses of <500 mg of sodium nitrate/kg body weight that were harmless to rats and dogs. The international estimates of nitrate intake from food are 31–185 mg/day in Europe and 40–100 mg/day in the United States. However, the Ministry of Health, Labour and Welfare of Japan reported that the average intake of nitrate in the Japanese population is around 200–300 mg/day, which is one and a half times to two times the ADI. Furthermore, according to a report by Hord, in which the daily nitrate and nitrite intakes were calculated based on the variations using the vegetable and fruit components of the DASH (Dietary Approaches to Stop Hypertension) dietary pattern, the level easily exceeds 1,200 mg/day nitrate. This is more than five-fold higher than the WHO’s ADI of 3.7 mg nitrate/kg body weight/day, and more than two-fold the US Environmental Protection Agency’s level of 7.0 mg nitrate/kg body weight/day for a 60 kg individual. Furthermore, as indicated in Figure 2, approximately 25% of the ingested nitrate is secreted in saliva, and 20% of the secreted nitrate in the saliva is converted to nitrite by commensal bacteria on the tongue, indicating that about 5% of the originally ingested nitrate is swallowed into the stomach. Therefore, for a DASH diet containing 1200 mg nitrate, an individual would be expected to swallow approximately 45 mg of nitrite a day, which easily exceeds the ADI of nitrite. Therefore, a comprehensive reevaluation of the health effects of dietary sources of nitrate/nitrite might be required in the near future.” (Kobayashi, 2015)
– Other International Views on Nitrite/ Nitrate from Dietary Sources besides from the USA and Europe
The Food Standards Australia New Zealand and the European Food Safety Authority concluded that the major sources of estimated nitrate and nitrite exposure, across different population groups, were vegetables and fruits (including juices). Processed meats only accounted for 10% of total dietary exposure to nitrite in the European survey. Consumption and exposure to dietary nitrate and nitrite is not considered an ‘‘appreciable health and safety risk’’, according to the Australian agency. (Keller, 2017)
Given the established vasoprotective, performance-enhancing, blood pressure lowering effects of dietary nitrates in humans, specific recommendations to encourage plant-based, nitrate-rich foods may produce significant public health benefits. (Keller, 2017)
Is vitamin C and E the crucial link that saves bacon’s bacon?
Three important nitrosamines, namely N-nitrosodimethylamine (NDMA), N-nitrosodiethylamine (NDEA), and N-nitrosomorpholine (NMOR), are classified as probably carcinogenic to humans (Group 2B) by the International Agency for Research on Cancer (IARC) (IARC 2000). (Erkekoglu, 2010)
Intrinsic antioxidant systems, such as protective enzymatic antioxidants as well as antioxidants available in the human diet, provide an extensive array of protection that counteract potentially injurious oxidizing agents. (Erkekoglu, 2010)
It was found that antioxidants protected the cells against nitrite and nitrosamines. (Erkekoglu, 2010) Dietary antioxidants can be a saviour when exposure to dietary genotoxic/carcinogenic compounds is the case. (Erkekoglu, 2010)
Erkekoglu, 2010 confirmed the DNA damaging effect of nitrosamines as shown in other studies (Robichová et al. 2004b; Arranz et al. 2006; 2007; Garcia et al. 2008a; b). Additionally, they used sodium nitrite to show the genotoxic effects of nitrite alone. They showed that antioxidants supplementation was capable of reducing both tail intensity and tail moment in all of the nitrosamine treatments, particularly in NDMA. They proposed that this may be related to antioxidants’ reduction of CYP2E1 and CYP2A6. They write, “CYP2E1 is responsible for α-hydroxylation of N-alkylnitrosamines with short alkyl chain, whereas cyclic nitrosamines like NPYR, NPIP, and NMOR may be activated by CYP2A6 and by CYP2E1 to a lesser extent (Kamataki et al. 2002). Furthermore, inhibition of CYP450 enzymes may not be the only mechanism underlying the protection of antioxidants. Alternative mechanisms by antioxidants may be as follows: ROS scavenging capacity, the conversion of reactive compounds to less toxic and easily excreted compounds, alteration of cell proliferation, stimulation of DNA-repair induced by nitrosamines, induction of Phase II enzymes, and NAD(P): quinine oxidoreductase activity (Roomi et al. 1998; Chaudière and Ferrari-Iliou 1999; Gamet-Payrastre et al. 2000; Surh et al. 2001; Surh 2002).” (Erkekoglu, 2010)
It is obvious that the overwhelming weight of evidence is that nitrite is not the destructive chemical that it was made out to be and that the negative media frenzy is completely misguided, to put it mildly. The health benefits of nitrate, nitrite and nitric oxide are clear. An obvious path for improving the geneneral healt and nutritional status associated with cured meats is the incorporation of vegetable and plant matter into its formulation. The fact that nitrire-free curing may possibly never be achieved has been raised and warrants further investigation. The next two segments will focus on N-nitrosamines and why the protein myaglobin evolved in such a way that it wants to react with oxygen and nitric oxide.
Want to Know More?
Gladwin, M. T., Kim-Sharipo, D. B.. (2008) The functional nitrite reductase activity of the heme-globins. Review in Translation Hematology, October 1, 2008. Blood (2008) 112 (7): 2636–2647. https://doi.org/10.1182/blood-2008-01-115261
Moncada, Salvador and Higgs, Annie. 1993. The L-Arginine-Nitric Oxide Pathway. New England Journal of Medicine doi: 10.1056/NEJM199312303292706 DO – 10.1056/NEJM199312303292706. Massachusetts Medical Society, https://doi.org/10.1056/NEJM199312303292706
Part of my series, the Truth About Meat Curing: What the popular media do NOT want you to know!
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Erkekoglu P, Baydar T. Evaluation of the protective effect of ascorbic acid on nitrite- and nitrosamine-induced cytotoxicity and genotoxicity in human hepatoma line. Toxicol Mech Methods. 2010 Feb;20(2):45-52. doi: 10.3109/15376510903583711. PMID: 20100056.
Ghasemi A, Zahediasl S. Is nitric oxide a hormone? Iran Biomed J. 2011;15(3):59-65. PMID: 21987110; PMCID: PMC3639748.
Gladwin, M. T. and Kim-Shapiro, D. B.. (2008) The functional nitrite reductase activity of the heme-globins. ASH Publication, Blood. Review in Translational Hematology. Blood (2008) 112 (7): 2636–2647. https://doi.org/10.1182/blood-2008-01-115261
Hlinský, Tomáš, Michal Kumstát, and Petr Vajda. 2020. “Effects of Dietary Nitrates on Time Trial Performance in Athletes with Different Training Status: Systematic Review” Nutrients 12, no. 9: 2734. https://doi.org/10.3390/nu12092734
Hord, N.G.; Tang, Y.; Bryan, N.S. Food sources of nitrates and nitrites: The physiologic context for potential health benefits. Am. J. Clin. Nutr. 2009, 90, 1–10.
Huizing M, Hackbarth ME, Adams DR, Wasserstein M, Patterson MC, Walkley SU, Gahl WA; FSASD Consortium. Free sialic acid storage disorder: Progress and promise. Neurosci Lett. 2021 Jun 11;755:135896. doi: 10.1016/j.neulet.2021.135896. Epub 2021 Apr 20. PMID: 33862140; PMCID: PMC8175077.
Keller, Rosa M. BS; Beaver, Laura PhD, MS; Prater, M. Catherine; Hord, Norman G. PhD, MPH, RD. Dietary Nitrate and Nitrite Concentrations in Food Patterns and Dietary Supplements. Nutrition Today: 9/10 2020 – Volume 55 – Issue 5 – p 218-226, doi: 10.1097/NT.0000000000000253
Keszler A, Piknova B, Schechter AN, Hogg N. The reaction between nitrite and oxyhemoglobin: a mechanistic study. J Biol Chem. 2008 Apr 11;283(15):9615-22. doi: 10.1074/jbc.M705630200. Epub 2008 Jan 17. PMID: 18203719; PMCID: PMC2442280.
Kobayashi, J. (2015) NO-Rich Diet for Lifestyle-Related Diseases, Article in Nutrients, June 2015, DOI: 10.3390/nu7064911
Kröncke KD, Fehsel K, Kolb-Bachofen V. Inducible nitric oxide synthase in human diseases. Clin Exp Immunol. 1998 Aug;113(2):147-56. doi: 10.1046/j.1365-2249.1998.00648.x. PMID: 9717962; PMCID: PMC1905037.
Lundberg JO. Nitrate transport in salivary glands with implications for NO homeostasis. Proc Natl Acad Sci U S A. 2012 Aug 14;109(33):13144-5. doi: 10.1073/pnas.1210412109. Epub 2012 Jul 31. PMID: 22851765; PMCID: PMC3421160.
Rassaf T, Ferdinandy P, Schulz R. Nitrite in organ protection. Br J Pharmacol. 2014 Jan;171(1):1-11. doi: 10.1111/bph.12291. PMID: 23826831; PMCID: PMC3874691.
Sindelar, J.J.; Milkowski, A.L. Human safety controversies surrounding nitrate and nitrite in the diet. Nitric Oxide 2012, 26, 259–266.
Vanek T, Kohli A. Biochemistry, Myoglobin. [Updated 2022 Jul 18]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK544256/
Zhou L, Zhu DY. Neuronal nitric oxide synthase: structure, subcellular localization, regulation, and clinical implications. Nitric Oxide. 2009 Jun;20(4):223-30. doi: 10.1016/j.niox.2009.03.001. Epub 2009 Mar 17. PMID: 19298861.