There are two separate factors that are important with respect to causes of stomach cancer.
One is environmental and the other is genetic. The environmental factors listed below in the table lead to a histological change of the lining of the stomach, called “intestinal metaplasia”, which means that there is a patch of lining having the appearance of small bowel lining, but surrounded by stomach lining. This is abnormal and the chronic irritation by stomach acid eventually leads to a form of scarring called “atrophy gastric”.
The end stage of this process over several years is then called “atrophic gastritis, which is associated with pernicious anemia. This condition is associated with vitamin B12 deficiency, but more importantly with gastric cancer. The genetic factors were suggested by the observation that people with blood group A have a higher rate of stomach cancer.
Even though women are normally less frequently plagued by stomach cancer, if a woman has blood group A there is an increased risk for stomach cancer. Also in younger patients, where normally stomach cancer is very rare, females belonging to the blood group A have an increased risk. This is an important fact, which should lead to regular gastroscopic screening in these women. There are certain families where stomach cancer is more common than in others. Such a historically well known family was the Bonaparte family, where Napoleon, his father and grandfather all died of gastric cancer (Ref. 1). The following table is composed from data based on Ref.1.
Risk factors for stomach cancer
| high nitrate or nitrite consumption | smoking |
| low vit. A and C diet | work (rubber industry, coal workers) |
| salted fish or meat | lack of refrigeration |
| low fat and low protein diet | old scars in stomach (previous surgery) |
| smoked foods | chronic helicobacter pylori infection |
| poor drinking water (well) | Gastric atrophy |
| genetic predisposition (rare) | Low social class |
Causes Of Stomach Cancer (Salted Fish)
Although there is a genetic predisposition in certain families as mentioned above, the main factors that cause stomach cancer are found in the food we eat, the water we drink, the cigarette smoke we inhale (if we smoke, but also to a lesser extent as secondary smoke), and the cancer producing substances (carcinogens) we get exposed to at work or in city streets. Some of the items above warrant a few comments:
- Nitrates and nitrites: These salts are used to preserve meats, sausages and even hard cheeses. It keeps the color of meat and sausages a bright red, very pleasing to the eye on the deli counter display. To my surprise I found that even my favorite Dutch Gouda cheese contained nitrates, so I had to look for a replacement with another cheese that does not contain nitrates or nitrites. Bear in mind that deli stores often do not display what is in the product they carry, so don’t be afraid to ask the attendant to show you the label of an unopened product. Stick to the products you know are safe. In the stomach the nitrates or nitrites are metabolized into the carcinogenic (=cancer causing) nitrosamines, which can cause stomach cancer (Ref. 4-6). The current understanding is that bacteria of the mouth and in the stomach under the influence of acid from the stomach secretions produce carcinogens. However, flossing and brushing of teeth as well as the use of mouthwash (Ref. 5) can significantly reduce the nitrosamine production in the stomach.
- Vitamin C and stomach cancer: Furthermore, relatively small amounts of vitamin C in the order of only 160 to 250 mg per meal can significantly reduce the amount of nitrosamine formation thus protecting us from stomach cancer. Instead of taking Vitamin C as a tablet it is much more enjoyable to take it as fruit or vegetables. So, if your grandmother or mother told you that fruit and vegetables are healthy for you, they were right in line with modern research on nitrosamine metabolism (Ref.4).
- Poor drinking water (wells): As is pointed out in Ref.6 nitrates are often high in poor well water and can lead to higher cancer rates including stomach cancer. However, special filter systems associated with water conditioners are available where the concentration of the water nitrates can be reduced or eliminated making it save to drink.
- Low fat and low protein diet: It may sound confusing that a low fat/low protein diet should be stomach cancer producing. What needs to be pointed out is the fact that with many of these diets they are very high in refined carbohydrates, as there are only these three components of food: carbohydrates, fat and protein.
- High refined carbohydrates (such as rice, pasta, potato products, sugar, cakes, candies etc.) are only empty calories with no fiber. The starch is very quickly broken down into sugar in the stomach, which gets absorbed rapidly into the blood stream. Insulin is produced as a response to this and with chronic intake of refined carbohydrates this leads to the syndrome of insulin resistance. Barry Sears explains in his book (Ref. 7) that hyperinsulinism is the cause of many cancers, heart attacks and autoimmune diseases. The simple dietary change to a zone type diet (Ref. 8) normalizes the insulin levels and brings the immune system function back to normal as well. This is accomplished by simply replacing refined carbohydrates by fruit and vegetable bound complex carbohydrates, which take sugar into the system by slow absorption thus avoiding overproduction of insulin. The end result is that the body’s immune system is strengthened instead of weakened and cancer may be prevented. At the same time cholesterol is lowered as well, which prevents heart attacks and strokes.
- Carcinogen exposure: Exposure to cancer producing substances (=carcinogens) can be due to direct exposure as it is the case with smoking. The carcinogens that accumulate on the tongue, in the oral cavity and on the pharynx are swallowed and irritate the mucous membrane lining in the stomach, which is very vulnerable to these noxious chemicals thus reacting in time by forming intestinal metaplasia and transforming this into gastric cancer. With smoked foods the carcinogen is also directly delivered into the stomach. Other carcinogens such as are found in the rubber industry and among coal workers. They are likely are first metabolized and circulate in the blood, and then affect the stomach lining causing stomach cancer. However, carcinogens can also come from sources that may not be that obvious such as food that was not properly refrigerated and that has become moldy. Some of these molds contain powerful carcinogens. This is the reason why we should not eat spoiled or moldy food.
- Old scars: In the past before the H-2-blockers came onto the market, stomach ulcers were treated with stomach surgery where a portion of the stomach was removed or a “drainage procedure” was done so that acid would be drained rather than retained in the stomach. The resulting internal scar in the stomach in a significant portion of these patients underwent a malignant transformation resulting in stomach cancer. Now that this is known a gastroenterologist will do a gastroscopy from time to time to monitor this and check with biopsies whether or not a high risk pattern is developing. If so, a revision surgery can be done before cancer actually hits.
- H. pylori is a bacterium that is present in a significant amount of the general population. However, only in 1% to 3% of those who carry this bacterium is stomach cancer developing.
References
1. Cancer: Principles &Practice of Oncology.4th edition. Edited by Vincent T. DeVita, Jr. et al. Lippincott, Philadelphia,PA, 1993. Chapter on Cancer of the stomach.
2. Cancer: Principles&Practice of Oncology. 5th edition, volume 1. Edited by Vincent T. DeVita, Jr. et al. Lippincott-Raven Publ., Philadelphia,PA, 1997. Chapter on Cancer of the stomach.
3. J Sun et al. Eur J Cancer Prev 2001 Feb;10(1):61-67.
4. SS Mirvish et al. Nutr Cancer 1998;31(2):106-110.
5. JM van Maanen et al. Cancer Detect Prev 1998;22(3):204-212.
6. JM van Maanen et al. Environ Health Perspect 1996 May;104(5):522-528.
7. B. Sears: “The age-free zone”.Regan Books, Harper Collins, 2000.
8. B. Sears: “Zone perfect meals in minutes”. Regan Books, Harper Collins, 1997.
9. K Murakami et al. Am J Clin Pathol 2001 Feb;115(2):224-34.
10. Y Tsubono et al. N Engl J Med 2001 Mar 1;344(9):632-636.
11. Conn’s Current Therapy 2004, 56th ed., Copyright © 2004 Elsevier
12. Ferri: Ferri’s Clinical Advisor: Instant Diagnosis and Treatment, 2004 ed., Copyright © 2004 Mosby, Inc
