Dietary Nitrates and Nitrites

Nitrate (NO3) and nitrite (NO2) have a long history as an effective way to preserve meat. Nitrate alone is not effective in the curing process until it has been chemically reduced to nitrite. Nitrite converts to nitric oxide (NO) in the curing process when it reacts with the pigment in meat. This reaction stabilizes the color associated with processed meat products like hot dogs, bacon, and ham. As food additives, these compounds also provide protection against the deadly bacteria Clostridium botulinum.

Dietary intake of nitrates and nitrites can increase the endogenous formation of N-nitroso compounds. Results from animal studies and mechanisms describing DNA damage suggest that these compounds may be carcinogenic in humans. However, a lack of compiled data on N-nitroso compounds in foods has hampered efforts to accurately measure intake.

Cancer prevention guidelines recommend limiting intake of processed meats, but researchers have not yet been able to determine the reason for an increased risk of some cancers. Nitrates and nitrites and their resulting N-nitroso compounds may be key, but cooking these foods at high temperatures has additionally been identified as a risk factor.

Nitrates and nitrites may also be obtained through soil and water. According to the American Academy of Pediatrics (AAP), formula prepared with well water may be contaminated with nitrates, putting infants at risk of methemoglobinemia or "blue baby syndrome." Nitrates are inorganic and cannot be destroyed by boiling, so if a family uses well water for drinking purposes, the AAP recommends the water be tested for nitrates. If nitrate levels are above a certain level, an alternative water source should be used to prepare infant formula and food.

Contrary to these concerns, there has been emerging evidence suggesting the conversion of dietary nitrate and nitrite from plant-based sources to nitric oxide may actually have beneficial effects in cardiovascular disease. Results have been promising in the lowering of blood pressure, as well as with boosting athletic performance; however, there remains a need for more studies of a longer duration.

Among recent studies, positive findings were noted in a clinical trial examining a small sample of healthy adults and nitrate intake from leafy green vegetables and beetroot juice. A significant decrease in blood pressure was associated with increased nitrate intake from these foods. Due to noted health concerns with N-nitroso compounds, researchers also tested for levels of these compounds in participant's urine. They found that levels increased with increased nitrate intake but remained within a clinically normal range.

An increase of clinical trials have also been reported by the National Institutes of Health's Office of Dietary Supplements, indicating improved performance for some athletes who supplemented with beetroot or beet juice; whereas other research noted no benefit or the improvement in endurance exercise was realized only by people who were active on a recreational basis. Although no safety concerns have been noted for moderate beetroot juice consumption for the short duration of these studies, gastrointestinal discomfort and urine discoloration have been reported.

For those wishing to increase their nitrate intake to gain any potential benefits, it is best to obtain it from nitrate-rich vegetables like leafy greens (or the roots of plants with leafy greens, like beets). Implications of emerging research aside, the recommendation to eat more vegetables is one of the tried and true recommendations for a healthy eating pattern.

References:

• Igoe RS, & Hui YH. Dictionary of Food Ingredients, 4th ed. Gaithersburg, MD: Aspen Publishers; 2001:98.
• National Institutes of Health, National Cancer Institute. Red Meat and Processed Meat Consumption. March 2020. Accessed June 4, 2020.
• Van der Avoort CMT, Jonvik KL, Nyakayiru J, et al. A Nitrate-Rich Vegetable Intervention Elevates Plasma Nitrate and Nitrite Concentrations and Reduces Blood Pressure in Healthy Young Adults. J Acad Nutr Diet. 2020. Article in Press.
• National Institutes of Health, Office of Dietary Supplements. Dietary Supplements for Exercise and Athletic Performance. Updated October, 2019. Accessed May, 2020.
• Thomas DT, Erdman KA, Burke LM. Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance. J Acad Nutr Diet. 2016;116:501-528.