DIET AND OTHER ENVIRONMENTAL RISK FACTORS IN THE DEVELOPMENT OF STOMACH CANCER
Gastric cancer is one of the most common cancers in the world. Although the etiology is unknown, environmental, genetic and familial factors, diet, Helicobacter pylori (Hp) and various predisposing conditions are blamed (1,2,3,4).
Gastric cancer formation is multifactorial. It is not known exactly how the events developed. However, excessive consumption of salty foods, low intake of ascorbic acid and carotenoids, and Hp are the main etiological factors (1,2,5) (Table-1) (Table-2).
Studies have shown that the rate of stomach cancer is low in populations that eat plenty of fresh vegetables and fruits, and it has been reported that the factor providing this is ascorbic acid (1,6). Ascorbic acid is actively secreted in the stomach. Ascorbic acid level was found to be low in the blood of people with intestinal metaplasia. Ascorbic acid concentration was found to be low in the stomachs of people with chronic atrophic gastritis and in gastric juice in the presence of high pH and Hp infection (1,5,6).
Carotenoids scavenge free radicals. They are thought to be anticarcinogenic in the late stage (6).
Table-1: Major factors associated with gastric cancer
Those with high cancer risk: Those with low cancer risk:
Family history of gastric ca ” blood group
“A” blood group Women, youth
Men, elderly Soft diet
Dry, salty fish, salty High vitamin C intake
and spicy foods Low cabbage diet
Low vitamin C intake Normal gastric secretion
High cabbage diet High socioeconomic
Achlorhydria level
Low socioeconomic status
Smoked foods
Low vitamin A
Smoking, alcohol intake
Premalignant lesions:
Atrophic gastritis, intestinal metaplasia,
dysplasia, gastric polyp,
partial gastrectomies (98 00703)
Barret’s esophagus
It has been stated that geographical conditions are also important in the development of gastric cancer. As a matter of fact, the incidence of gastric carcinoma decreases by 25% in those who immigrated from Japan to the United States, and 50% in the children of those who immigrated. Despite the fact that the immigrants gained western-type eating habits, the incidence of gastric cancer was still higher than the local population. However, the rate of disease in their 2nd and 3rd generation children is decreasing progressively and is approaching the rates in indigenous people. A similar situation is seen in those who immigrated from Eastern Europe to the USA. On the other hand, the incidence of the disease increases in those who immigrated to Japan (8).
Gastric cancer is the most common type of cancer in both men and women in Japan, and it constitutes the largest group among all cancers with 20-30% (1).
It has been reported that the incidence of gastric cancer has decreased in both men and women in some industrialized western countries in recent years (9). In studies conducted in the United States of America (USA), stomach cancer was reported to be 1.5-2.5 times more common in African-Americans and Native American tribes than in white American citizens (10).
Although the incidence of gastric cancer has decreased in recent years, it still maintains its importance in the world. It has been reported that it is most common in Japan, China, Iceland, Finland, Austria, South America and Eastern European countries (1,2,7). In our country, stomach cancer ranks 5th with a rate of 6.68% in men, 7th with a rate of 5.9% in women, and first among digestive system cancers, according to the data of the Ministry of Health between 1986-1990 (8,11). In a study conducted at Ankara University Faculty of Medicine on 3136 cancer cases in 1990, it was shown that stomach cancer is the second most common after lung cancer with a rate of 9.43% in men, and the third after breast cancer and lymphomas with a rate of 6.70% in women (11).
Genetic and environmental risk factors:
There are important indicators showing the role of genetic factors in the pathogenesis of gastric cancer. It is known that gastric cancer is more common in some families. For example, Napoleon, Napoleon’s father and grandfather, and several of his siblings died of stomach cancer (12). Patients with hereditary nonpolyposis colorectal cancer (Lynch Syndrome Type II) are also at higher risk of developing gastric cancer (13). In addition, the risk of developing gastric cancer in first-degree relatives of patients with gastric carcinoma is 2-3 times higher (14,15). In addition, there are publications reporting that the incidence of gastric cancer is high among people belonging to the “A” blood group. However, it has been reported that diffuse type gastric carcinoma is more common in these (16).
Studies suggest that one or more environmental factors in early life contribute to the development of intestinal type gastric cancer, especially (17,18).
The risk of stomach cancer all over the world is also proportional to the socio-economic status of the society. There is a relationship between low socioeconomic status and high cancer risk. However, it is difficult to understand the relationship between cancer and factors such as a large family, poor hygiene conditions and malnutrition (10,19,20).
Distal esophagus and cardia adenocarcinomas are more common in societies with high socioeconomic status. The reason for this cannot be explained (21).
Diet:
It is difficult to explain the relationship between diet and cancer. However, studies have shown that the incidence of gastric cancer is low in populations that generally eat a diet rich in fresh vegetables and fruits. On the other hand, it is known that foods rich in salt, smoking, alcohol and poorly preserved foods increase the risk of gastric cancer (22-27). In studies conducted in Japan, it has been reported that there has been a recent decrease in deaths due to gastric cancer, and this is due to the increase in consumption of fresh vegetables and fruits, as well as the decrease in consumption of dried and salty foods, in addition to technological developments (1,19). It has been shown in animals that a high-salt diet causes gastric atrophy (28). It has been reported that excessive salt intake and long-term use of foods that have been preserved by salting can also lead to atrophic gastritis and lead to cancer development (29).
It has been reported that intestinal type gastric cancers have decreased recently in the USA and western European countries. This decrease is thought to be related to environmental factors and diet (1,5). It has been reported that especially intestinal type gastric cancers are associated with excessive salt intake, dried or pickled foods. These foods reduce acid secretion by creating atrophy in the gastric mucosa, and thus anaerobic bacteria multiply, and the formation of carcinogen N-nitroso compounds increases with the effect of these bacteria (5).
It is mutagenic with low consumption of fruits, especially citrus fruits, and green and fresh vegetables and insufficient intake of antioxidant substances that inhibit the formation of vitamin C, other vitamins and N-nitroso compounds in these fruits and vegetables. and carcinogenic events are increasing (5,30). In recent years, there has been a decrease in the incidence of intestinal type gastric cancers, with the increase in consumption of fresh vegetables and fruits and the consumption of fresh foods, the widespread use of freezing and storage, and therefore the decrease in the use of pickled or salted foods in Western countries (5).
It has been shown that foods rich in nitrite and salt lead to the development of metaplasia in humans (31). It has been shown in animals that it causes stomach tumors by transforming into N-Nitroso form with the intake of foods rich in nitrates, nitrites and secondary amines (32). Due to chronic atrophic gastritis and intestinal metaplasia, anaerobic bacteria, which often form colonies in the stomach, convert nitrites and nitrates into N-nitroso derivatives, which are more potential carcinogenic agents (19,32).
Nitrites and nitrates were previously used frequently for long-term storage of meat, fish and vegetables. However, recently, the rate of nitrites and nitrates in food has been reduced by 75% in the USA and industrialized countries (19,32). However, the roles of nitrites and nitrates in carcinogenesis and the physiopathology have not yet been fully explained (33).
Freezing storage of food reduces the risk of stomach cancer. Freezing food increases the availability of vegetables and fruits. Thus, the need to store the food by salting or similar methods is eliminated. Ice cream indirectly causes a decrease in the incidence of gastric cancer by preventing the contamination of food by bacteria and fungi, which may cause the activation of various procarcinogenic substances (19,34).
Many studies have shown that the development of gastric cancer increases 1.5-3 times in smokers. However, its relationship with the amount smoked has not been clearly demonstrated. Similarly, it has been shown that gastric dysplasia and other potential premalignant lesions are more common among smokers (26,31,35,36,37,38,39).
In summary, there is a large correlation between intestinal type gastric cancers and environmental factors that a person is exposed to at an early age. Hp infection, diet poor in vegetables and fruits, too salty foods, poorly stored foods cause gastric mucosal damage and atrophic gastritis (5,22,24). In addition, mucosal damage caused by intraluminal bacteria, procarcinogens activated by bacteria or other carcinogens may also lead to metaplasia, dysplasia and eventually gastric carcinoma (1,5).
The main reasons for the decrease in the incidence of distal-intestinal type gastric cancers in the world are listed as follows (1);
- Decrease in the prevalence of many environmental factors that can cause gastric cancer,
- The widespread use of freezing food,
- Advanced techniques in food storage.
Proximal, diffuse type gastric cancers, on the other hand, maintain the same prevalence in high and low risk regions of the world and their incidence does not decrease, unlike the distal ones. These cancers may also be associated with other factors that have not yet been defined (1).
