Before we discuss how nitrates and nitrites affect dogs, we have to put on our chemistry caps.
Chemistry of Nitrates and Nitrites
Nitrates and nitrites are chemical compounds that consist of nitrogen and oxygen.
A nitrate is made of a bond between a single nitrogen atom and three oxygen atoms.
A nitrite is a bond between a single nitrogen atom and two oxygen atoms.
Nitric oxide is a single nitrogen atom bonded to a single oxygen atom.
Where Are Nitrates and Nitrites Found?
Nitrates are naturally high in certain vegetables such as leafy vegetables, beetroot juice and celery.
Nitrogen is critical in both synthetic fertilizer and organic fertilizer like manure and vegetable compost. Through oxidization – or bonding with air – the nitrogen is transformed into nitrates.
Nitrates are also found in fertilizers.
When too much fertilizer is applied to crops, builds up over time or is mismanaged, the nitrates runoff into bodies of water or seep into groundwater. Wells are particularly vulnerable.
Nitrogen and phosphorus from this runoff cause dead zones in major bodies of water like the Gulf of Mexico. Too much nitrogen and phosphorous spark algae growth that can have ripple effects through the aquatic system such as affecting the reproductive health of fish.
Nitrites can enter water through the use of corrosion inhibitors in industrial process water or chloramination, which may give rise to the formation of nitrite.
Nitrites and nitrates are added to processed meats like deli meats and hot dogs as a preservative against certain bacteria and to preserve color.
The World Health Organization (WHO) and many researchers warn against eating too many processed meats because the nitrites and nitrates may increase one’s chances to develop cancer.
When processed meats like bacon and hot dogs are heated, the nitrites interact with the amino acids and cause another chemical to be formed, nitrosamines. Nitrosamines are carcinogenic.
Blue Baby Syndrome
On one side of the argument, we have WHO and major scientists stating that excess intake of well water high in nitrates can lead to “blue baby syndrome” (methemoglobinemia or nitrate/nitrite poisoning).
Others contend that methemoglobinemia was not caused by nitrate, but by fecal bacteria that infected the infants and produced nitric oxide in their guts. The premise is that nitrite reacts with hemoglobin to produce methemoglobin, which is no longer able to carry oxygen.
By the way, the Environmental Protection Agency (EPA) has set a limit of 10 milligrams per liter of nitrate-nitrogen in drinking water. Some researchers are saying that this limit should be lowered by 50% to 5 milligrams per liter of nitrate-nitrogen in drinking water.
Other adverse medical conditions have been associated with drinking contaminated water such as adverse reproductive outcomes, diabetes and thyroid diseases. Nitrates inhibit iodide uptake by the thyroid, potentially disrupting thyroid function.
Other researchers do not contend with all of that specific evidence However, they say that the human body can tolerate more nitrates and nitrites than the current advisory thresholds. Specifically, they point to natural vegetable sources and the importance of nitrates and nitrites.
“Huh?” You ask. Yes.
Bacteria in the mouth and gut convert nitrate into nitrite. In the gut, the nitrite curbs opportunistic bacteria.
Then, the nitrite is converted into nitric oxide. Nitric oxide is an important signaling molecule in the body that helps lower blood pressure. Additionally, studies have shown that nitrates found in vegetables can increase sports performance – particularly running.
Many scientists reply that these are not good reasons to increase recommended dietary amounts of nitrates and nitrates for entire populations, but only for specific populations with specific needs.
What about Animals and Nitrate Poisoning?
Keeping with the most widely adopted scientific theory that nitrates cause methemoglobinemia, the disease is caused by an excess intake of nitrates in many other animal species – particularly cows. This is commonly known as nitrate poisoning.
Cattle and sheep are ruminant animals – they have a four-chambered stomach. This makes them more susceptible to nitrate poisoning because bacteria present in the rumen convert nitrate to nitrite. The conversion of nitrate to nitrite happens quickly in a cow’s rumen than the reduction of nitrite to ammonia. Consequently, when ruminants consume plants high in nitrate, some nitrite formed in the rumen enters the bloodstream where it converts blood hemoglobin to methemoglobin. This reduces the oxygen-carrying capacity of blood, and the animal suffers from oxygen starvation of the tissues.
Chicken and pigs are nonruminant animals so they eliminate nitrate in their urine.
Think about it this way, poultry litter can be used as fertilizer on grazing grasses for cattle, but should be limited to reduce the risk of nitrate poisoning.
Just like humans, horses, rabbits and dogs are monogastric – meaning we have single chambered stomachs. So while we and they are not as susceptible to nitrate poisoning as cattle, there is still that possibility.
We know that dogs can develop methemoglobinemia, but what about other diseases associated with an overabundance of nitrate intake?
Unfortunately, most summaries published by the United States government agencies and WHO reference experiments conducted prior to 1990 that more than likely need to be updated. We attempted to find more recent published studies.
A research study published in 1973 by Kelley et al. stated that, “Continuous consumption of these sublethal levels of nitrate did not produce a syndrome of chronic nitrate toxicosis characterized by thyroid dysfunction.”
WHO appeared to think otherwise based on studies with Wistar rats as well as some deficiencies in the study.
Due to the mounting evidence in human medicine that nitrates and nitrites can affect the thyroid gland, we believe that a newer study or survey of dogs must be completed.
De Laforcade et al. conducted a limited study to find out if nitric oxide concentrations were higher in dogs with either chronic valvular disease (CVD) or dilated cardiomyopathy (DCM) compared to healthy controls, and to determine whether nitric oxide concentrations are correlated with type of cardiac disease, disease severity, medical therapy, or serum tumor necrosis factor (TNF) and interleukin‐1 (IL‐1).
Blood was collected from 32 dogs with DCM, from 10 dogs with CVD, and from 10 healthy controls.
Mean nitrate and nitrite concentrations were significantly higher in dogs with heart disease than in controls.
Nitrate and nitrite concentrations in dogs with cardiac disease were not correlated with type or severity of cardiac disease, medication type, or TNF and IL‐1 concentrations.
The results of this study suggest that metabolites of nitric oxide are increased in some dogs with cardiac disease, but these increases appear to be independent of disease severity, immune response marker cytokines (TNF and IL‐1 concentrations), and type of pharmacologic intervention.
However, a study from 1994 looked at the role of nitric oxide in the regulation of oxygen consumption. This group of researchers chose a specific nitric oxide synthesis inhibitor, nitro-L-arginine (NLA). What they discovered after injecting conscious dogs with NLA intravenously was:
- Increases in oxygen extraction, oxygen consumption, and blood pressure
- Increases in total peripheral resistance (also known as systemic vascular resistance, which is the resistance to blood flow throughout the entire vascular systems, but excludes pulmonary.)
- Elevated body temperature
- Decreases in oxygen saturation, oxyhemoglobin, cardiac output, and heart rate
There are not many comprehensive cancer studies in dogs regarding the possible connection to nitrites and nitrates. We were able to find two studies that confirmed the findings seen in human medicine.
Turkish researchers published a study in 2012 that determined that malignant canine mammary tumors are accompanied by an elevation of nitric oxide whereas healthy dogs did not have the same finding.
A 2015 study out of Brazil also looked at mammary cancer and found that nitrates and nitrites were significantly higher in dogs with mammary carcinoma compared to the cancer-free control group.
What Should I Do about the Sources of Nitrates and Nitrites?
We suggest that if your community is under a nitrate advisory in drinking water that you give your companion dog the same water you would drink. One option is bottled water. Another option is to install a reverse osmosis system in your house. According to the NSF International – an organization that sets industry standards – this is the preferred and best method. However, it is costly.
Are you wondering about nitrates and nitrites in dog food? We are covering that next. Stay tuned!
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