Nitrates (NO3) and nitrites (NO2) are chemical compounds consisting of nitrogen and oxygen atoms, found naturally in the environment and the human diet. While nitrates are relatively stable, nitrites pose a health concern, especially when consumed in excess. These substances are common in water sources from agricultural runoff and are used as preservatives in cured meats, but they also occur naturally in high concentrations in many vegetables. The primary concern is that nitrites can react with other compounds in the body to form N-nitrosamines, which are classified as probable human carcinogens.
Understanding Nitrate Processing and Natural Excretion
The body handles ingested nitrates through a continuous, multi-step process involving enterosalivary circulation. After nitrates are absorbed into the bloodstream, about 25% is concentrated in the salivary glands and secreted into the mouth via saliva. Oral bacteria then convert a small portion (5% to 10%) of this nitrate into nitrite.
The resulting nitrite is swallowed and enters the acidic stomach. Here, nitrite can be converted into beneficial nitric oxide, which helps regulate blood pressure and blood vessel dilation, or it can react with amines to form N-nitrosamines.
The body efficiently eliminates excess nitrates primarily through the kidneys. Most nitrate that is not converted or reabsorbed is excreted in the urine. Approximately 60% to 70% of an ingested dose is cleared from the body within the first 24 hours.
Dietary Interventions to Reduce Nitrate Levels
Focusing on diet can enhance the body’s ability to manage and eliminate nitrates and block the formation of harmful byproducts. One effective strategy involves consuming antioxidants, which act as nitrite scavengers in the digestive system.
Antioxidant Consumption
Antioxidants like Vitamin C and polyphenols chemically interfere with the process that turns nitrites into N-nitrosamines. Vitamin C is potent, blocking this conversion and reducing the formation of these compounds in the stomach. Many vegetables naturally high in nitrate, such as spinach and kale, also contain high levels of Vitamin C and polyphenols, mitigating the risk from their nitrate content. Incorporating foods like citrus fruits, bell peppers, kiwi, and strawberries provides the necessary Vitamin C.
Supporting Clearance Mechanisms
Supporting the body’s natural clearance mechanisms is another important dietary intervention. Because the kidneys excrete the majority of unbound nitrates, maintaining high hydration is paramount. Drinking sufficient water helps the kidneys function optimally, ensuring waste products, including nitrates, are flushed out. While the liver is not directly responsible for nitrate excretion, supporting overall liver function aids general detoxification processes. Foods rich in sulfur compounds, such as garlic, onions, and cruciferous vegetables, can help maintain these pathways.
Strategies for Minimizing Nitrate Exposure
Reducing the amount of nitrate entering the body is the most direct long-term strategy for minimizing internal levels.
Water Source Management
A major source of exposure is contaminated drinking water, especially in rural areas using private wells. Testing well water regularly is advisable, as nitrates are odorless, tasteless, and fluctuate due to factors like agricultural runoff. For water sources with elevated nitrate levels above the safe limit of 10 mg/L, common filters like carbon filters are ineffective. The most reliable removal methods are reverse osmosis (RO), ion exchange, and distillation. An RO system forces water through a fine membrane, physically blocking nitrate molecules and typically removing 80% to 95% of the contaminant.
Food Source Reduction
Another significant source of intake comes from cured and processed meats, where nitrites are added as preservatives. Minimizing consumption of products like bacon, hot dogs, and deli meats reduces exposure to added nitrites. When these processed meats are cooked at high temperatures, the added nitrites are more likely to form N-nitrosamines.
Proper Vegetable Handling
Proper handling of high-nitrate vegetables also reduces potential nitrite exposure. While vegetables are generally protective due to their antioxidants, improper storage of cooked items like spinach and beets allows bacteria to convert nitrate into nitrite. Cooked leftovers should be refrigerated promptly (within two hours) to slow bacterial activity. Boiling vegetables can also reduce nitrate content by allowing the water-soluble compound to leach out, provided the cooking water is discarded.