Nitrates, Cancer, Lunch Meat, and Celery — Should You Worry?

Nitrates and nitrites are chemically related to one another, and are commonly used as preservatives in a variety of food items. Bacon is perhaps the most notable example, but many packaged, processed meats — including many lunch meats — are among those that contain nitrates and nitrites. Even “natural” lunch meats, which don’t list nitrates or nitrites on the ingredients label, can contain dried celery juice. This is a natural source of nitrates and nitrites.

First and foremost, nitrates and nitrites, while not chemically identical, are implicated in similar health consequences. This is because a chemical reaction converting nitrate into nitrite takes place in human saliva. Approximately 5% of ingested nitrate is converted to nitrite in the saliva of adults and children, while approximately 10% of ingested nitrate is converted to nitrite by infants (Spiegelhalder et al). The problem is that nitrites then go on to engage in a variety of undesirable chemical reactions. For one thing, they can react with chemicals called secondary amines to produce new compounds called nitrosamines. Nitrosamines are carcinogenic (cancer-causing) in animals (Swann et al), and there’s very good evidence — in fact, the relatively conservative Linus Pauling Institute of Oregon State University goes so far as to say there’s “an enormous amount of evidence” — to suggest they’re carcinogenic in humans as well (though of course, for obvious ethical reasons, no controlled scientific studies have been done). Secondary amines, put very succinctly, make up proteins, which in turn make up a major portion of the structural and functional componentry of every living cell. In short, living creatures have an abundance of secondary amines in the body, meaning that there’s no barrier to formation of carcinogenic nitrosamines upon the consumption of nitrites or nitrates. Meats are also made up of protein, which means a meat preserved with nitrate or nitrite salt contains all the necessary ingredients for nitrosamine formation.

Cancer-causing nitrosamines aren’t the only reason to be concerned about nitrates and nitrites; they can cause methemoglobinemia (“Blue-Baby Syndrome”) as well. This results from the reaction of nitrites with hemoglobin, which is the protein in red blood cells that binds to oxygen and carries it to the tissues. The reacted hemoglobin, called methemoglobin, can’t carry oxygen as efficiently. While one of the major causes of Blue-Baby Syndrome is consumption of formula made with nitrate-rich water by infants under 6 months of age (often water that is polluted by fertilizer runoff and other sources of nitrates), there have been reports in the literature of nitrites from vegetables leading to the syndrome (Sanchez-Echaniz et al). The Sanchez-Echaniz study reported on cases of methemoglobinemia in infants up to 13 months of age, which is troubling, but the vegetables in question were homemade purees that had been stored for some time (as opposed to fresh vegetables). Because there’s considerable evidence to suggest that nitrites and nitrosamines can cross the placenta (see, for instance, Gruener et al, Althoff et al), pregnant women are generally advised to avoid nitrate- and nitrite-containing foods during pregnancy. Interestingly enough, however, maternal consumption of high-nitrate water during lactation doesn’t appear to increase nitrate levels in breast milk (Dusdieker et al). The study did not report on nitrite or nitrosamine levels in breast milk, however.

Because a certain amount of exposure to nitrates and nitrites is unavoidable — they’re naturally-occurring, such that even avoiding processed food isn’t a mechanism for completely eliminating them from the diet — it’s more useful to discuss how much nitrate and nitrite is safe, rather than whether nitrate and nitrite are safe. The EPA standards for nitrates and nitrites in drinking water are set at no more than 10 mg/L and 1 mg/L, respectively. The dose of nitrate considered “safe” by the EPA is 1.6 mg/kg daily, while that for nitrite is 0.1 mg/kg daily. For a 15-pound baby (perhaps an average 6-month-old), that correlates to no more than 10.9 mg of nitrate and 0.68 mg of nitrite daily. Dietary nitrate and nitrite intake vary significantly with eating habits, but vegetables are the most major source of dietary nitrates in most individuals (White), providing just over 80% of total daily nitrate. Spinach, raw lettuce, and cooked beets are among the highest in nitrate concentration (van Velzen et al), with celery only slightly behind (White). All in all, an “average” adult likely gets about 86 mg/day of nitrate and 0.2 mg/day of nitrite from vegetables, in addition to 16 mg/day of nitrate and 3.92 mg of nitrite from cured meat. Given the 5% conversion, give or take, of nitrate in vegetables and meat to nitrite, the vegetables contribute a total of about 4.5 mg/day of nitrite, while cured meats contribute a total of about 4.72 mg/day of nitrite. This suggests that cured meats, while not the most significant source of dietary nitrates, are nevertheless the most significant source of dietary nitrites in most adults. If an average adult gets about 9.22 mg/day of nitrite from all sources (which is above the “safe” dose of 6.8 mg/day for a 150-pound adult), then clearly the average diet is a bit too high in nitrite for absolute safety’s sake. Because of the many health benefits associated with consuming vegetables, however, it isn’t reasonable to suggest reducing vegetable consumption (or even consumption of high-nitrate vegetables, like spinach) on these grounds. Cured meats, however, do not serve a unique and important dietary function, and it is therefore reasonable to suggest limiting cured meat consumption. Consuming a normal quantity of vegetables on a daily basis while reducing cured meat consumption to no more often than every other day is a reasonable mechanism for staying within EPA-suggested nitrate and nitrite limits.

The final question is whether nitrates and nitrites are any healthier if they come from celery as opposed to from added nitrate and nitrite salts. This is a bit difficult to quantify, because meat companies don’t report the amount of nitrate and nitrite in their product, but it’s reasonable to assume that the total quantity of preservative is probably similar, regardless of whether it comes from celery (as in “natural” meats) or from added sodium nitrate and sodium nitrite. Compared to a meat preserved with sodium nitrite, meat preserved with celery juice is probably safer. This is because the conversion of nitrate to nitrite is so inefficient, and because celery contains nitrate rather than nitrite. Compared to a meat preserved with sodium nitrate, however, a meat preserved with celery juice likely has very similar total nitrate concentration, as as such, there would be little difference between the two. These are speculations, but they’re reasonable and measured speculations.

 

Science Bottom Line:* Don’t cut down your vegetable consumption because you’re worried about nitrates and nitrites, but consider eating lunch meat no more than every other day. Be aware that there are nitrate and nitrite preservatives in some other foods as well (generally processed ones), so read packages carefully. Celery-preserved meats are probably better than nitrite-preserved meats, but may be quite similar to nitrate-preserved meats.

 

Do you watch for nitrates and nitrites in your diet?

 

References:

Althoff et al. Transplacental effects of nitrosamines in Syrian hamsters: I. Dibutylnitrosamine and nitrosohexamethyleneimine. Z Krebsforsch Klin Onkol Cancer Res Clin Oncol. 1976 May 3;86(1):69-75.

Dusdieker et al. Does increased nitrate ingestion elevate nitrate levels in human milk? Arch Pediatr Adolesc Med. 1996 Mar;150(3):311-4.

EPA Drinking Water Contaminants. Accessed 1 Nov 2011.

EPA Nitrate. Accessed 1 Nov 2011.

EPA Nitrite. Accessed 1 Nov 2011.

Gruener et al. Methemoglobinemia induced by transplacental passage of nitrites in rats Bull Environ Contam Toxicol. 1973 Jan;9(1):44-8.

Linus Pauling Institute Nitrosamines and Cancer. Accessed 1 Nov 2011.

Sanchez-Echaniz et al. Methemoglobinemia and consumption of vegetables in infants. Pediatrics. 2001 May;107(5):1024-8.

Spiegelhalder et al. Influence of dietary nitrate on nitrite content of human saliva: Possible relevance to in vivo formation of N-nitroso compounds. Food Cosmet Toxicol. 1976 Dec;14(6):545-8.

Swann et al. Nitrosamine-induced carcinogenesis. The alklylation of nucleic acids of the rat by N-methyl-N-nitrosourea, dimethylnitrosamine, dimethyl sulphate and methyl methanesulphonate. Biochem J. 1968 Nov;110(1):39-47.

van Velzen et al. Relative significance of dietary sources of nitrate and nitrite. Toxicol Lett. 2008 Oct 1;181(3):177-81. Epub 2008 Aug 3.

White, J. Relative significance of dietary sources of nitrate and nitrite. J Agric Food Chem. 1975 Sep-Oct;23(5):886-91.