Understanding Nitrates and Nitrites
Nitrates are chemical compounds composed of nitrogen and oxygen atoms that are part of the natural nitrogen cycle. They are found naturally in soil, water, and many vegetables, such as spinach, celery, and beets. Nitrates are relatively stable. The primary health concern arises when nitrates are converted into nitrites, which happens through the action of bacteria, either in the environment or in the human body, particularly in the mouth and gut. It is the nitrite ion that is responsible for most of the associated health risks. Nitrites are also added to processed meats as preservatives.
Methemoglobinemia: A Risk for Infants
One of the most well-known and acute risks of nitrates is methemoglobinemia, often called “blue baby syndrome”. This condition primarily affects infants under six months of age. In infants, the stomach environment is less acidic, which allows for the growth of bacteria that can rapidly convert ingested nitrates to nitrites. These nitrites are then absorbed into the bloodstream where they can oxidize the iron in hemoglobin, the molecule responsible for carrying oxygen in red blood cells. This oxidized form of hemoglobin, known as methemoglobin, cannot effectively transport oxygen, leading to cyanosis—a blue-gray discoloration of the skin—and potentially serious illness or death. The risk is particularly high for infants fed formula prepared with water from private wells that have high nitrate concentrations, typically over the EPA's safety standard of 10 mg/L.
The Link Between Nitrates, Nitrites, and Cancer
For decades, researchers have investigated the potential link between nitrate and nitrite intake and cancer risk. The concern stems from the fact that nitrites can react with amines and amides (compounds found in protein-rich foods like meat) in the acidic environment of the stomach to form N-nitroso compounds, some of which are known carcinogens.
The International Agency for Research on Cancer (IARC) classifies ingested nitrate and nitrite, under conditions that result in endogenous nitrosation, as "probably carcinogenic to humans" (Group 2A). A 2022 French study found that higher intakes of food additive nitrates and nitrites were associated with higher risks of breast and prostate cancer, respectively. However, the evidence remains complex. Studies often show mixed or inconclusive results, partly because many factors influence cancer development, and dietary sources of nitrates vary widely.
It is important to differentiate between different sources. Nitrates from processed meats are associated with higher risks, while nitrates from vegetables are generally not. This is because vegetables often contain protective antioxidants, like vitamin C, that can inhibit the formation of harmful N-nitroso compounds.
Environmental Contamination and Drinking Water
Drinking water can be a major source of nitrate exposure, especially for rural residents who rely on private wells. Nitrate contamination often comes from agricultural runoff (fertilizers and manure), septic systems, and landfills. Shallow or poorly constructed wells are most vulnerable. This can pose a risk for methemoglobinemia in infants and, according to some studies, other health effects in adults from long-term, low-level exposure. Regular testing of well water is a critical safety measure.
The Role of Nitrates in Processed Meats
Nitrates and nitrites are added to cured meats, such as bacon, sausage, and deli meats, to serve several purposes.
- Preservation: They are powerful antimicrobial agents that inhibit the growth of pathogenic bacteria, most notably Clostridium botulinum, which causes botulism.
- Flavor: They contribute to the characteristic savory taste of cured meats.
- Color: They give processed meats their pink color by reacting with myoglobin.
However, it's the nitrates and nitrites in these processed products that are most associated with increased cancer risk, particularly colorectal cancer, due to the formation of N-nitroso compounds. While some products are labeled "uncured" or "no added nitrates," they often use celery powder, a natural source of nitrates, which the body processes in the same way.
Symptoms of Nitrate Overexposure
Severe or acute nitrate poisoning, particularly methemoglobinemia, can present with distinct symptoms. In infants, the most obvious sign is the blue-gray discoloration of the skin and lips. In more severe cases or with higher occupational exposure, symptoms can also affect adults.
Symptoms of Methemoglobinemia
- Bluish or gray skin tone, especially around the mouth, nose, and lips.
- Lethargy and irritability.
- Shortness of breath.
- Vomiting.
- Rapid or elevated heart rate.
Symptoms of High Occupational Nitrate Exposure
- Headaches.
- Dizziness and lightheadedness.
- Low blood pressure (hypotension).
- Reflex tachycardia (rapid heart rate).
Nitrates from Different Food Sources: A Comparison
To understand the health implications, it is crucial to recognize that the source of nitrates matters due to the presence of other compounds, such as antioxidants.
| Feature | Processed Meats (Bacon, Ham) | Vegetables (Spinach, Beets) |
|---|---|---|
| Source | Added nitrates/nitrites, often from synthetic or celery powder sources. | Naturally occurring nitrates from the soil. |
| Associated Antioxidants | Few or none. | High in protective antioxidants like Vitamin C and polyphenols. |
| Formation of Nitrosamines | Higher risk due to reaction with high protein content and processing methods. | Lower risk, as antioxidants inhibit nitrosamine formation. |
| Cancer Risk | Associated with an increased risk of certain cancers, particularly colorectal cancer. | Some studies show an inverse relationship with certain cancers due to overall health benefits. |
| Overall Health Impact | High in sodium and saturated fat; generally considered less healthy. | Part of a healthy diet, offering vitamins, minerals, and fiber. |
Conclusion
While nitrates are naturally present in our environment and diet, the risks of nitrates are predominantly linked to high exposure, particularly from contaminated drinking water and processed meats. For infants, contaminated well water is a serious and well-documented threat for methemoglobinemia. For adults, the potential carcinogenic risk is most strongly associated with nitrites in processed meats, where they can react to form nitrosamines. In contrast, the nitrates found in vegetables are not considered a major risk and are consumed alongside protective antioxidants. To mitigate risks, limit consumption of processed meats and ensure your water sources, especially private wells, are regularly tested for nitrate levels. For more information on nitrate and nitrite toxicity, consult the CDC's Toxic Substances Portal(https://wwwn.cdc.gov/TSP/ToxFAQs/ToxFAQsDetails.aspx?faqid=1186&toxid=258).
