The World Cancer Research Fund (WCRF) 2007 stated that the consumption of processed meat is a convincing cause of colorectal cancer (CRC), and therefore, the public should avoid it entirely. Sodium nitrite has emerged as a putative candidate responsible for the CRC-inducing effects of processed meats. Sodium nitrite is purported to prevent the growth of Clostridium botulinum and other food-spoiling bacteria, but recent, contradictory peer-reviewed evidence has emerged, leading to media reports questioning the necessity of nitrite addition. To date, eleven preclinical studies have investigated the effect of consuming nitrite/nitrite-containing meat on the development of CRC, but the results do not provide an overall consensus. A sizable number of human clinical studies have investigated the relationship between processed meat consumption and CRC risk with widely varying results. The unique approach of the present literature review was to include analysis that limited the human studies to those involving only nitrite-containing meat. The majority of these studies reported that nitrite-containing processed meat was associated with increased CRC risk. Nitrite consumption can lead to the formation of N-nitroso compounds (NOC), some of which are carcinogenic. Therefore, this focused perspective based on the current body of evidence links the consumption of meat containing nitrites and CRC risk.

The preservative sodium nitrite is added to processed meat with the intention of preventing the growth of Clostridium botulinum, but this also influences product flavour and colour. The World Health Organisation has declared nitrites to be ‘probably carcinogenic’. Use is permitted by the European Union but its addition is limited to 100 mg/kg in all processed meat, except bacon, which is limited to 175 mg/kg. At present, there is no independent peer-reviewed literature assessing the residual nitrite levels in bacon in the United Kingdom. Furthermore, this is the largest study of residual nitrite concentrations in bacon that has ever been conducted. A total of 89 different commercially available bacon samples were collected, and analysed using flow injection analysis to determine their residual nitrite content. The mean residual nitrite concentration for all bacon samples was 10.80 mg/kg. Residual nitrite levels did not differ between smoked and unsmoked bacon. Middle cut bacon (26.00 mg/kg) had significantly higher residual nitrite concentrations than back bacon (8.87 mg/kg; p = 0.027), and medallion bacon (4.47 mg/kg; p = 0.008). This study shows that there is large variation in the mean residual nitrite levels of bacon sold in the UK and all the reported values are within current regulatory limits. Despite this, it appears that many manufacturers could decrease the amount that they are currently using in their products.