Vitamin C reduces the risks of developing colon cancer

Colon cancer is the 2^nd most common cancer in Canada.  Processed meats such as kovbasa, ham and sausages significantly increase the risk of developing colon cancer.  But vitamin C eaten with these processed meats can reduce that risk.  Please read below for a thorough discussion of the research.

Colorectal cancer is the second most common cancer in Canada. 1 in 13 men, and 1 in 16 women will be diagnosed with colorectal cancer in their lifetime. 94% of colorectal cancers occur in adults over the age of 50 (1). The Canadian Cancer Society has stated that in 2017, 26,800 Canadians were diagnosed with colorectal cancer, and 9,400 died from it. Every day, an average of 73 Canadians were diagnosed with colorectal cancer, and 26 died from it.

One of the known risk factors for colorectal cancer is a diet high in processed meat, due to the added preservatives. The nitrites and nitrates added to the meats are used as additives to extend shelf life, prevent microbial contamination, give the meat its pink colour and improve its quality. The amount of nitrates/nitrites added to the meat depends on cooking methods, other additives, wood smoke, spices, heat, storage and packaging. Foods containing high amounts of nitrates include bacon, cold cuts, salami, hot dogs, sausages, and smoked and salted fish (2,3). Once consumed, these nitrates are converted into N-nitroso compounds (NOCs) within the digestive tract, which are carcinogenic compounds (4,5). In particular, cells of the colon are susceptible to the oxidative damage caused by NOCs, and the colon contains a high amount of amines and amides which are involved in the nitrate conversion process (5).

Studies comparing the consumption of vegetarian diets vs. processed and red meat diets have shown significantly increased risk of developing colorectal cancer with processed meat diets, measured by the higher levels of fecal NOCs (5). Every 50 gram/day increase in processed meat is associated with a 21% increased risk of colorectal cancer (4).

Sources of vitamin C, as well as other antioxidants and phytochemicals found in fruits and vegetables have been shown to prevent the formation of NOCs in the digestive tract and alleviate the nitrate-induced oxidative damage, therefore protecting against cancer (3,6). Some, but not all processed meats contain vitamin C and α-tocopherol in their ingredients, which can decrease the nitrite content of the meat (2). Research has shown that in people with low vitamin C intake, the risk of digestive cancers are higher, whereas if taking vitamin C prior to nitrite consumption, the DNA damage is reduced (3,5). The time of consuming the two is also an important factor. 1 gram of vitamin C taken 2 hours before, with, 1 hour after, or 2 hours after the nitrate exposure has been shown to reduce the NOC activity by 94, 100, 87 and 25%, respectively (6). Therefore vitamin C is most effective in reducing the negative effects of the nitrates when taken in consumption with the processed meats (6).

References:

1. https://www.canada.ca/en/public-health/services/publications/diseases-conditions/colorectal-cancer.html
2. Cantwell M, Elliott C. Nitrates, Nitrites and Nitrosamines from Processed Meat Intake and Colorectal Cancer Risk. Journal of Clinical Nutrition & Dietetics. 2017 December 18; 3(4):27
3. Knekt P, Jarviven R, Dich J, Hakulinen T. Risk of colorectal and other gastro-intestinal cancers after exposure to nitrate, nitrite and N-nitro compounds: a follow-up study. International Journal of Cancer. 1999 November 8; 80(6)
4. Chan DSM, Lau R, Aune D, Vieira R, Greenwood DC, Kampman E, Norat T. Red and Processed Meat and Colorectal Cancer Incidence: Meta-Analysis of Prospective Studies. PLoS ONE. 2011 June 6; 6(6)
5. Joosen AMCP, et al. Effect of processed and red meat on endogenous nitrosation and DNA damage. Carcinogenesis. 2009 June 4; 30(8)1402-1407
6. Mirvish SS. Experimental evidence for inhibition of N-nitroso compound formation as a factor in the negative correlation between vitamin C consumption and the incidence of certain cancers. Cancer Research. 1994 April 1; 54:1948-1951