The carcinogenic risks associated with cigarette smoking are a major reason smokers are warned that they are liable to die young.

These risks are most strongly sourced from toxic carcinogens known as Tobacco Specific Nitrosamines (TSNA) which, like its name implies, are found uniquely in tobacco products. That means cigarettes, snuff, smokeless tobacco, and electronic cigarettes all contain TSNA.

But just how do TSNAs become so dangerous? What are the dangers TSNAs pose to the health? And what curing methods produce these dangerous carcinogens in tobacco?

We’ll be examining the transformation process of nitrates to their more dangerous offshoots - TSNAs, the grave health risks associated with the consumption of TSNAs, and how the storage process of tobacco affects the content of TSNAs present within it.

How do nitrates become TSNAs?

Despite being the most common carcinogens present in tobacco, TSNAs do not exist naturally in the tobacco leaves where they are sourced.

These Tobacco Specific Nitrosamines are the product of the curing and fermentation of tobacco.  They appear after tobacco has been harvested and dried (cured) to produce optimum quality and character from the tobacco leaf. The formation process usually begins a few days after harvest, with TSNAs forming when tobacco alkaloids (nicotine, nornicotine etc) are nitrosated.

It is during this process that notable TSNAs — N-nitrosonornicotine (NNN) and  4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) are formed. These carcinogens have been confirmed to induce cancer of the nasal cavity, lungs, esophagus, and liver in laboratory rats

Types of tobacco curing processes

The tobacco curing process usually depends on the type of tobacco in question. They include:

i. Flue-curing: this process is used to dry Virginia tobacco. It requires the use of heat sourced from pipes or furnaces to dry tobacco leaves hung to dry.

ii. Air curing: with this process, tobacco leaves are left to dry in well-ventilated barns over the course of 6-8 weeks. This is typically used for burley leaves.

iii. Sun curing: used in color curing oriental leaves, this process requires tobacco leaves to be dried out, uncovered in the sun for around 2 weeks.

During these curing processes, the chemical reactions necessary to transform tobacco nitrates into TSNAs occur. It is believed that the higher the temperature and humidity, the higher the levels of TSNAs in the tobacco leaves.

How High Do TSNA Levels Go In Tobacco?

As we’ve seen, TSNA levels are heavily dependent on the curing methods used in removing chlorophyll and drying up the tobacco plant for consumption.

To determine the levels of these dangerous carcinogens in tobacco, we’ll be sharing the results of a Chinese study carried out to determine the effect of storage temperature and nitrate levels on TSNA formation. Here were some findings:

Sun-cured tobacco: the TSNA content increased substantially while the tobacco was placed under natural storage conditions. i.e left uncovered to dry out in the sun.

Air-cured tobacco: with TSNA content proven to increase in warmer weather conditions during curing, it was revealed that barley tobacco experienced a 772% jump in TSNA content after going through a treatment of 60° for 24 days, when compared to lower temperature conditions.

Flue-cured tobacco: it was revealed that after 36 days, the TSNA content in this tobacco did not increase, despite the high-heat it was subjected to.

It is worth noting that this method of curing is widely used in the production of US cigarettes.

Another study has noted that the TSNA levels of tobacco leaves are dependent on the part of the plant. It showed that NNK and NNN levels are higher in the midrib than in the lamina in air-cured tobacco, whereas flue-cured tobacco showed the opposite. Other times, the tobacco in question can influence the TSNA levels — with flue-curing producing three times the TSNA content in bright tobacco, compared to air-drying methods.

Effects of TSNAs

Tobacco Specific Nitrosamines are dangerous compounds listed among the harmful and potentially harmful constituents (HPHC) of tobacco products. As one of tobacco’s most potent carcinogens, it has been linked to cancers in various parts of the body like the lungs, esophagus, pancreas, liver, and nasal cavity.

These dangers are further compounded by the fact that other carcinogenic compounds are present in tobacco. These include PAHs and aromatic amines which lead to an increased risk of skin, gastrointestinal, bladder, and breast cancer combined.

With tobacco killing eight million people annually, with around 600,000 of those deaths being linked to second-hand smoke exposure, the need for legislation to regulate the amount of harmful chemicals present in tobacco has become absolutely necessary in preserving the lives of literally millions of people.

Legislation to regulate TSNA content in tobacco

The effects of nitrosamines and far-reaching. Though TSNAs are exclusive to tobacco, nitrates can be found in multiple sources, food being one.

Recognizing the dangers present in nitrosamines, beginning from the 1970s the FDA held regular meetings to review their heavy presence in foods like bacon, sausage and ham. These caused changes in processing that saw their reduced levels in foods and beverages containing nitrosamines.

The tobacco industry also recognized the pressing need to reduce the nitrosamines content in its products. Through concerted effort, significant reductions have occurred in TSNA levels.

From 1980 - 1992, the average reduction of individual TSNAs came down about 83%. Between 1990 and 2007, finished product nitrosamines declined significantly.

Further on,  in 2017, the FDA proposed a plan to regulate the amount of NNN in smokeless tobacco products.

This measure is expected to prevent in the next 20 years: around 12,700 new cases and 2200 oral cancer related deaths.

Despite these efforts however, high levels of TSNAs persist in tobacco products. This has led to continued appeals for standard of manufacture that will ensure reduced levels of TSNAs are present in tobacco products.