How Do Tobacco-Specific Nitrosamines Differ From Nitrosamines in Food?

Nitrosamines are often found in grilled meat and processed cheese. Image by Oddjob (Own work) [Public domain], via Wikimedia Commons

Every human being on this planet has been exposed to a wide variety of nitrosamines since birth. Nitrosamines are notoriously known as cancer-causing compounds that frequently find their way into the food we eat, such as deep-fried fish and grilled meat, and the beverages we drink, such as beer. What's more, the nitrosamines in latex products, such as surgical gloves, balloons and condoms, are generally benign compared to those found in tobacco leaves.

How Nitrosamines in Food are Formed

Nitrosamines in meat and cheese are formed from nitrite, which is commonly used in pickling.

In foods, nitrosamines are produced from nitrites and secondary amines, which often occur in the form of proteins. Their formation can occur only under certain conditions, including strongly acidic conditions such as that of the human stomach. High temperatures, as in frying, can also enhance the formation of nitrosamines. The presence of nitrosamines may be identified by the Liebermann nitroso reaction (not to be confused with the Liebermann's reaction).

Under acidic conditions the nitrite forms nitrous acid (HNO₂), which is protonated and splits into the nitrosonium cation N≡O⁺ and water: H₂NO₂⁺ = H₂O + NO⁺. The nitrosonium cation then reacts with an amine to produce nitrosamine.

So, what are the kinds of food that may contain dangerous nitrosamines? Here's a list courtesy of a cancer research paper published in 1983:

Foods which have been shown to contain volatile nitrosamines include cured meats, primarily cooked bacon; beer; some cheeses; nonfat dry milk; and sometimes fish. It should be emphasized that not all samples analyzed contain detectable amounts of nitrosamines. When present, the volatile nitrosamines usually occur in the lower microgram/kg range. Estimates by several investigators suggest that the average daily intake of volatile nitrosamines from foods is approximately 1 microgram/person.

Nitrosamine Formation in Cigarettes and E-Liquids

Tobacco-specific nitrosamines or TSNAs are "formed from nicotine and related compounds through a nitrosation reaction, which occurs during the curing and processing of tobacco."

Because of nitrosation, cigarette smoke and regular tobacco have significantly high levels of nitrosamines. In comparison, only trace amounts of the chemical have been found in nicotine-containing products, such as gums, patches and e-liquids, and in "smokeless" tobacco products, such as chewing tobacco and dipping tobacco.

The most carcinogenic TSNAs are 4-(methylnitrosamino)1-(3-pyridyl)-1-butanone (NNK) and N-nitrosonornicotine (NNN). Research studies have shown that NNK is the foremost carcinogen that promotes systemic lung cancer and tumors of the nasal cavity, liver, and pancreas in rats. Meanwhile, the nitrosamine known as NNN has been identified as the primary cause of esophageal cancer in rats, and respiratory tract tumors in hamsters and mink. A combination of these two inevitably leads to the development of oral tumors in rats.

Traces of Tobacco-Specific Nitrosamines in E-Liquids

Recently, Dr. Farsalinos and his team found traces of nitrosamines in some e-liquids they tested. These carcinogenic compounds are formed from nicotine, which is extracted from tobacco leaves. The researchers, however, didn't know whether the nitrosamines they found were created during the heating process of the e-liquid or is it during the extraction process of nicotine from tobacco. They say that the aerosol samples had zero nitrosamines in them because the e-liquids had minimal TSNAs to begin with. Also, heating up tobacco leaves without the need of fire and oxygen can also produce nitrosamines.