Other than tobacco, food is the best-known source of nitrosamines. Food contains nitrite and proteins from which nitrosamines can be formed. In the body, nitrite is produced from nitrate, which occurs naturally in vegetables. Nitrate and nitrite are sometimes added to food products to improve shelf life or for colouring.
NNN/NNK/nitrosamines in tobacco smoke
The amount of NNN and NNK that is formed from nitrite and amines in tobacco depends on the type of tobacco and the way it is grown, dried and processed. Factors that lead to higher levels of NNN and NNK in tobacco are the use of a particular type of tobacco (Burley), use of the main vein of the tobacco leaf, and certain processing techniques such as treating the leaves with smoke and storing them damp.
Processed tobacco has a higher concentration of NNN and NNK than unprocessed tobacco. NNN and NNK are present in tobacco and are released when a tobacco product is smoked. The amounts of NNN and NNK in tobacco smoke can vary widely. For instance, in a filter cigarette, the filter removes a portion of the NNN and NNK, leading to smaller amounts of these two substances being inhaled.
Adverse health effects
NNN and NNK are among the most important substances that cause smoking-related cancer. In the body NNN and NNK are broken down by enzymes, enabling them to damage DNA. If this damage is not repaired, it can lead to the development of cancer, especially in the lungs or airways. It has been shown in laboratory animals that this can also lead to cancer in the foetus. Additionally, NNN and NNK can stimulate the growth of cells with damaged DNA, which in turn can stimulate the growth of a cancerous tumour. Nitrosamines have been classified by the International Agency for Research on Cancer (IARC) as ‘carcinogenic to humans’ (Group 1). Because these effects can occur even with small amounts, no safe levels can be set for nitrosamines or specifically for NNN or NNK. However, since measurement techniques are becoming increasingly more accurate, a maximum level is often set for food products and pesticides.
Nitrosamines in foods can have the same impact on health as nitrosamines in tobacco smoke. However, the levels of nitrosamines in food are so low that the European Food Safety Authority (EFSA) has concluded that exposure to nitrate through vegetables is unlikely to lead to health risks. This conclusion does not apply to tobacco.