Nitrates and nitrites are two distinct chemical compounds that are often a source of public confusion. Both are found naturally in certain foods and are also used as additives in others, prompting questions about their effects on human health. These compounds are related, but their roles within the body and their ultimate health impacts can be quite different.
Chemical Structures and Common Sources
At a molecular level, the distinction between nitrate and nitrite is straightforward. Nitrate (NO3) consists of one nitrogen atom bonded to three oxygen atoms, while nitrite (NO2) has only two. This difference makes nitrate a more stable compound compared to the more reactive nitrite. Both are inorganic, water-soluble compounds that often exist as salts.
The majority of dietary nitrate intake, approximately 80%, comes from natural sources. Leafy green vegetables are particularly rich in nitrates, with spinach, arugula, and lettuce containing high concentrations. Root vegetables like beets and celery are also significant sources. Nitrates can also be found in drinking water, often as a result of agricultural runoff.
Nitrites are most widely known as additives in food processing, commonly added to cured meats like bacon, hot dogs, and ham. They act as a preservative against harmful bacteria, contribute to the pink or red color of cured meats, and add a distinctive flavor. While most dietary nitrites come from these additives, small amounts are also produced within the body.
The Body’s Conversion Process
Once consumed, a significant portion of the nitrate we eat is absorbed from the small intestine into the bloodstream. The circulatory system transports this nitrate throughout the body, where about 25% is taken up by the salivary glands and secreted back into the mouth. Here, oral bacteria play a direct role in chemical conversion.
These oral bacteria possess enzymes that convert the relatively inert nitrate (NO3) into the more reactive nitrite (NO2). Roughly 5% to 10% of ingested nitrate becomes nitrite through this enterosalivary pathway. The newly formed nitrite is then swallowed, traveling down to the highly acidic environment of the stomach.
Upon reaching the stomach, nitrite can follow one of two main pathways. One path is its conversion into nitric oxide (NO), a signaling molecule with various physiological functions. Alternatively, nitrite can react with amines, which are abundant in protein-rich foods, to form N-nitroso compounds, more commonly known as nitrosamines.
Health Risks Associated with Nitrosamines
Nitrosamines are created when nitrites encounter amines, especially in the acidic setting of the stomach. The risk of this conversion is amplified by high-temperature cooking methods like frying or grilling. This is why processed meats, which contain both added nitrites and naturally occurring amines, are a focal point of health concerns.
Many nitrosamines are identified as probable carcinogens in humans. Research links the consumption of processed meats to a higher risk of developing cancers like colorectal cancer, leading international health organizations to classify processed meat as carcinogenic to humans.
While nitrites added to meat are a source of concern, they can also form from nitrates naturally present in other foods or drinking water. The ultimate risk depends on factors like the amount consumed, other dietary components, and individual physiology.
Health Functions of Nitric Oxide
In contrast to the risks from nitrosamines, the conversion of nitrite into nitric oxide (NO) is a beneficial pathway. This process is a reason why nitrate-rich vegetables are associated with positive health outcomes. Nitric oxide is a signaling molecule that performs numerous functions, and nitrate from plants is a significant source for its production.
One of the most well-documented roles of nitric oxide is vasodilation, the relaxation and widening of blood vessels. By relaxing the inner muscles of blood vessels, nitric oxide allows blood to flow more freely, which can lead to a reduction in blood pressure. This effect contributes to cardiovascular health, and studies confirm dietary nitrate can improve blood circulation.
Beyond cardiovascular benefits, nitric oxide is also involved in improving physical performance. Enhanced blood flow means more efficient delivery of oxygen and nutrients to muscles during exertion. Studies show that consuming nitrate-rich foods, such as beetroot juice, can improve endurance and oxygen efficiency during exercise.
The vegetables that supply nitrates also contain antioxidants like vitamin C. These antioxidants help steer the conversion of nitrite toward producing beneficial nitric oxide while inhibiting the formation of harmful nitrosamines. This dual action explains why nitrates in whole plant foods are considered healthy, and why manufacturers now add substances like vitamin C to cured meats to mitigate risk.