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Questions About The Diets

Blood Groups, Nitrates and Nitrites


Why does smoking or curing foods produce nitrates or nitrites?


Nitrate (NO3) is a naturally occurring form of nitrogen found in soil. Nitrogen is essential to all life, and most crop plants require large quantities to sustain high yields. The formation of nitrates is an integral part of the nitrogen cycle in our environment. In moderate amounts, nitrate is a harmless constituent of food and water. Normally, nitrates are converted to nitrites by bacteria in the saliva and the back of the tongue.

Nitrites are though to be problematic because they can be converted into nitrosamines compounds with known carcinogenicity. This reaction definitely occurs in the test tube: Whether it occurs in the human digestive tract is not yet clear. Research has demonstrated that vitamin C (ascorbic acid) can inhibit the reaction of nitrites with amines or amides. It competes with the amine for the nitrite, which inhibits carcinogenic compound formation. However, I would recommend the use of food-derived vitamin C (acerola or rose hips) over synthetic.

Nitrates and nitrites are compounds typically found in smoked or cured meats, though they can be found in many vegetables as well. The main significance of nitrites and nitrates is that they my be linked to cancer of the stomach. However, there may be evidence that this link is oversimplified. New research indicates that moderate amounts of nitrates are not only safe, but may protect humans and animals against potentially fatal infections from microbes such as salmonella, shigella and E. coli.

Cancer of the stomach, or gastric cancer, is a disease in which stomach cells become malignant (cancerous) and grow out of control, forming a tumor. Almost all (95%) of stomach cancers start in the glandular tissue that lines the stomach. The tumor may spread along the stomach wall or may grow directly through the wall and shed cells into the bloodstream or lymphatic system. Once beyond the stomach, cancer can spread to other organs.

The link between nitrates and stomach cancer is probably strongest for blood group A individuals, since that groups has been known since the 1950's to have higher levels of stomach cancer than the others. (1) Type A's with stomach cancer have the most uniform supression of anti-Tn antibodies. Anti-Tn antibodies usually serve to protect against the earliest changes in the mutational process.

It has been hypothesized that the mechanisms behind the association between blood group A and gastric carcinoma is that the carcinoma cells produce an antigen immunologically related to blood group A, which particularly in O-individuals may have a protective effect by preventing the growth and spread of the tumor.

If you are group O, the relationship with nitrosamines can be just as lethal, since H. pylori infection is associated with an increased risk of stomach cancer as well, and evidence suggests that group O individuals have a greater inflammatory response against H. pylori than the other blood groups.

  1. Hoskins LC, Loux HA, Britten A, Zamcheck N. Distribution of ABO blood groups in patients with pernicious anemia, gastric carcinoma and gastric carcinoma associated with pernicious anemia.N Engl J Med. 1965 Sep 16;273(12):633-7.

The Ask Dr. D'Adamo internet advice column ran from 1996 to 2009, at which time Dr. D'Adamo's teaching and programming responsibilities no longer allowed him to devote time and resources to directly answering visitor questions. However we've recently reorganized this treasure-trove of material and made it again available to his readership. He occasionally posts new entries. These are marked with a NEW tag.

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