What is the mechanism by which smoking causes gastric cancer

People understand that smoking can cause lung cancer because smoke has to be filtered through the lungs and toxic substances are absorbed by the lungs, causing long-term irritation to the lungs and inducing lung cancer. But when it comes to smoking being a risk factor for gastric cancer, many people don't quite understand. How can the smoke itself induce gastric cancer if it doesn't enter the stomach?

In fact, people have a wrong understanding that only when smoke comes into direct contact with the stomach will it cause poisoning to the stomach. In fact, this is not the case at all. After smoke enters the human lungs, it can be filtered and absorbed by the alveoli, and the toxic substances in the smoke enter the human blood circulation system.

These toxic substances contain oxidants and free radicals, which can consume the body's protective antioxidants, ascorbic acid, carotene, etc. These substances have anti-cancer effects. The antioxidants in the blood of smokers are generally lower than those of non-smokers.

In addition, the harmful components in the smoke that enters the respiratory tract can be absorbed by the respiratory mucosa and enter the blood, thereby damaging the blood vessels in the stomach. Moreover, the toxic substances in the smoke can enter the stomach directly along with saliva and food, and the benzopyrene, dimethylnitrosamine, phenols and other substances, including nicotine, carbon monoxide and tar, can directly irritate the gastric mucosa, promote the formation of gastritis and gastric ulcers, and delay their healing. Gastric ulcers that do not heal for a long time may become cancerous.

Smokers are also often infected with Helicobacter pylori, which can aggravate intestinal metaplasia and atypical hyperplasia of chronic atrophic gastritis. In addition, Helicobacter pylori itself is carcinogenic.