by Mary Saucier Choate, M.S., R.D., L.D.
Dietitian & Food and Nutrition Educator
For years, we have heard about the cancer-causing risks of nitrates and nitrites as food additives. As a result of a question asked by a Co-op meat department employee, I have journeyed through the science and marketing of these compounds in order to explain clearly what they are, what they do, and whether or not they are a health concern when found in foods.
Sodium nitrite is an anti-oxidant used to cure meats like ham, bacon, and hot dogs. It gives cured meats their characteristic color and flavor. Nitrite prevents spoilage, stops the growth of botulism-causing bacteria, and can help thwart harmful Listeria monocytogenes. The amount of nitrite allowed by USDA to be added to cured meats is limited to 156 parts per million. After processing, the amount of nitrite remaining in the final product is typically 10 parts per million or less.
Mention nitrates and nitrites, and the average consumer thinks of processed and cured meats. Yet, less than five percent of our daily nitrite intake actually comes from cured meats.
Approximately 80 percent of dietary nitrate comes from the naturally occurring nitrates in the vegetables and fruit we eat.
The nitrate content differs among kinds of produce and fluctuates with soil conditions and the amount and kind of fertilizer used. The amount of nitrate in some vegetables can be very high. Spinach, radishes, and lettuce, for example, may contain nitrate concentrations of 500 to 1,900 parts per million, depending on the vegetable.
Researchers are studying whether dietary nitrates and nitrites from vegetables and fruit may add to the blood pressure-lowering effects of the Dietary Approaches to Stop Hypertension (DASH) diet. They found that some combinations of the DASH diet pattern exceed the World Health Organization’s Acceptable Daily Intake for nitrate by 550 percent.
Nearly 100 percent of the nitrate we eat is converted to nitrite in the body by specialized bacteria in the mouth and gastrointestinal tract. Nitrite in saliva, as well as dietary nitrite, is swallowed into the stomach where it is converted to nitric oxide and other metabolic products that have beneficial actions. These include relaxing blood vessels, decreasing blood pressure, supporting heart and blood vessel function, preventing injury from heart attack, promoting wound healing, and destroying harmful bacteria in the gut.
The evidence against nitrates and nitrites as carcinogens seems to be less certain than previously as these compounds are studied more rigorously. A May 2001 report by the National Institutes of Health’s National Toxicology Program concluded that there was no evidence of carcinogenic activity applicable to humans in the rat models studied. In fact, they noted decreased incidence of mononuclear cell leukemia. The June 2010 update to the respected California Environmental Protection Agency’s report on “Chemicals Known to the State to Cause Cancer or Reproductive Toxicity” did not list sodium nitrite or nitrate.
On the other hand, the World Cancer Research Fund/American Institute for Cancer Research (WCRF/AICR) Expert Report: Food, Nutrition, Physical Activity and the Prevention of Cancer: a Global Perspective looked at thousands of population studies on diet and cancer and concluded that “The evidence that red meats and processed meats are a cause of colorectal cancer is convincing.”
A closer look at the studies used, however, shows them to be less convincing. These experts looked at studies that compare similar population groups to see which ones get a disease compared with those that don’t. In this kind of study, there is always the problem of differences between the two groups not accounted for, differences that may be the actual cause of the disease. In most analyses of this nature, the authors state these potential problems in their conclusions. But this expert report does not discuss the possibility for confounding factors, such as the fact that someone eating the highest amount of processed meat—in some cases more than five and a half ounces a day—may have other eating and lifestyle behaviors that might add to the cancer risk, such as a lack of fruits, vegetables, and whole grains in the diet.
Many researchers studying the benefits of nitrates and nitrites to heart and artery health have noted this and other weaknesses in the associations found between processed meats and cancer.
Concern continues to exist about potentially cancer-causing nitrosamines, which can be formed when nitrite-containing meats are heated to very high temperatures. For this reason, in processed meat products, ascorbic acid or sodium ascorbate (forms of vitamin C) or sodium erythorbate (from sugar) are added in combination with nitrite to prevent the formation of nitrosamines.
If you want to avoid nitrates and nitrites in processed meats, you must look deeper than the “no nitrates added” claims.
“Natural” and certified organic processed meat products are not allowed the direct addition of nitrite or nitrate and must be labeled “uncured.” However, if the product contains plant ingredients such as natural flavorings or spices, celery juice or celery juice concentrate, or other vegetable powders and concentrates, there is a potential contribution of nitrate from these sources. When the nitrate in these natural sources is exposed to certain types of bacteria in the product, the plant nitrate is converted to nitrite.
Adding nitrate-containing plant ingredients, instead of conventional sodium nitrite, allows for a “no nitrates added” or “nitrate-free” label but may still mean that nitrites are present in the product. The level will be lower than conventionally cured products, but still a surprise for those expecting a nitrate-free product.
Information from all of our processed meat vendors was not complete at the time of writing, but please watch our website and the deli counter for a brochure that will list which items we carry that do not contain naturally occurring plant nitrates and those that do.
Hopefully, the above information has made clear that nitrates and nitrites in processed meat contribute very little of the nitrates and nitrites we eat, compared with the nitrates in vegetables and fruits. So should we eat hot dogs and salami with abandon? Well, no, because of the company they keep.
Processed meats are usually high in sodium and saturated fat. The science behind the effect on heart health of these two food components has only grown stronger. Sodium raises blood pressure, especially as we age, and saturated fat leads to elevated cholesterol levels and clogged arteries. Processed meats should be enjoyed as an occasional treat, not an everyday staple.
For more information, please see below for the resources that were used in this article.
Nitrates and Infant Poisoning Risk
The rare, but serious, occurrence of excess nitrates in food or water fed to infants can be dangerous, causing nitrate poisoning known as “blue baby syndrome.” The presence of excess nitrate in the infant’s blood diminishes the oxygen-carrying ability of hemoglobin.
The American Academy of Pediatrics recommends well water testing for nitrate content, since the greatest risk of nitrate poisoning occurs in infants fed well water contaminated with high nitrate levels. The nitrate nitrogen concentration of the water should be less than10 parts per million.
The organization states that infants fed commercially prepared infant foods generally are not at risk of nitrate poisoning as these are tested for nitrate content. However, they recommend that home-prepared vegetables (such as spinach, beets, green beans, squash, carrots) which can vary widely in nitrate content, should be avoided until infants are three months or older. The group also points out that there is no reason to introduce solid foods beyond breast milk or formula earlier than four to six months of age.
Food, Nutrition and the Nitric Oxide Pathway. Nathan S. Bryan (Editor): DesTech Publishing – Pennsylvania, September 2009
Perspective: Food sources of nitrates and nitrites: the physiologic context for potential health benefits. Norman G Hord, Yaoping Tang, and Nathan S Bryan. Am J Clin Nutr 2009 90:1; pages 1-10. http://www.ajcn.org/content/90/1/11.full.pdf+html
National Toxicology Program Technical Report On The Toxicology And Carcinogenesis Studies Of Sodium Nitrite In F344/N Rats And B6c3f1 Mice (Drinking Water Studies)
National Institutes of Health Publication No. 01-3954, May 2001 http://ntp.niehs.nih.gov/ntp/htdocs/LT_rpts/tr495.pdf
State Of California Environmental Protection Agency, Office Of Environmental Health Hazard Assessment, Safe Drinking Water And Toxic Enforcement Act Of 1986, Chemicals Known To The State To Cause Cancer Or Reproductive Toxicity, June 11, 2010
Natural and Organic Cured Meat Products: Regulatory, Manufacturing, Marketing, Quality and Safety Issues by Joseph Sebranek and James Bacus, American Meat Science Association, White Paper Series Number 1, March, 2007
Junkfood Science: What’s the evidence cancers are our own fault?
The World Cancer Research Fund/American Institute for Cancer Research (WCRF/AICR) Expert Report: Food, Nutrition, Physical Activity and the Prevention of Cancer: a Global Perspective. Part 2: Evidence and judgments
Infant Methemoglobinemia: The Role of Dietary Nitrate in Food and Water
Frank R. Greer, MD, Michael Shannon, MD the Committee on Nutrition and the Committee on Environmental Health. Pediatrics Vol. 116 No. 3 September 2005, pp. 784-786 Reaffirmed February 1, 2010.
Dietary nitrate in man: friend or foe?
McKnight GM, Duncan CW, Leifert C, Golden MH.
British Journal of Nutrition. 1999 May;81(5):349-58.
Dietary nitrate in Japanese traditional foods lowers diastolic blood pressure in healthy volunteers
Tanja Sobko a,b,*, Claude Marcus b, Mirco Govoni c, Shigeru Kamiya
Nitric Oxide 22 (2010) 136–140