Smoking is a high risk factor for lung cancer. It is estimated that 1/3 of the world’s smokers are in China. At least 85% of lung cancer patients have a history of smoking, and squamous and small cell carcinomas rarely occur in those without tobacco exposure.The risk of lung cancer in smokers increases with the following factors.
1. the amount of smoking.
2. age of initiation of smoking.
3. the level of inhalation.
4, tar and nicotine content of tobacco.
5, the presence or absence of a filter, no filter cigarettes have a higher risk than filtered cigarettes.
In the United States, about 15% of lung cancer patients have no history of tobacco exposure, and these people tend to have adenocarcinoma. The lung cancer mortality rate for smokers is 10-15 times higher than for nonsmokers, and a history of tobacco exposure, including so-called “secondhand smoke,” also increases the incidence of lung cancer. Among non-smokers who develop lung cancer, 1/3 live with a smoker.
There are over 3,000 chemicals in tobacco, and multi-chain aromatic hydrocarbons (e.g., benzo(a)pyrene) have strong carcinogenic activity. In addition to lung cancer smoking is associated with the occurrence of lip, tongue, oral cavity, esophagus, stomach, colon, pancreatic, kidney, and cervical cancers. Clinical studies and animal studies have shown that the carcinogens in smoke can also affect the fetus through the placenta, resulting in a significantly higher incidence of cancer in the offspring.
The main carcinogenic components in tobacco are as follows.
1. polycyclic aromatic amines (benzo(a)pyrene, diphenylanthracene).
2.Oxybenzoarsines.
3.N-nitrosamines (NNK).
4.Aromatic amines.
5.Heterocyclic aromatic amines.
6.Aldehydes.
7.Other organic compounds.
8, inorganic compounds (hydrazine).
These compounds act on certain specific enzymes within human tissues (especially lung tissue), producing mutations in the structure of cellular molecules (e.g. DNA), possibly with mutations in K-ras.
Smoking is a major risk factor for many cardiovascular and cerebrovascular diseases and is more harmful to women than to men. Smoking in women can cause menstrual disorders, difficulties in conception, ectopic pregnancy, low estrogen, osteoporosis and early menopause. Smoking in pregnant women can cause spontaneous abortion, fetal growth retardation and low birth weight. Other conditions such as preterm labor, stillbirth, early placental abruption, and placenta praevia may be associated with smoking. Smoking during pregnancy can increase fetal mortality before and after birth and the incidence of congenital heart disease.
These hazards are due to carbon monoxide and other harmful substances in smoke entering the fetal bloodstream, forming carboxyhemoglobin and causing hypoxia; at the same time, nicotine constricts blood vessels, reducing the fetal blood supply and nutrient supply, thus affecting the normal growth and development of the fetus. Ninety percent of lung cancers, 75 percent of COPD and 25 percent of coronary heart disease in women are related to smoking. The rate of death from breast cancer is 25% higher in women who smoke than in non-smoking women.
Nicotine has been shown to lower sex hormone production and kill sperm, reducing sperm count, morphological abnormalities and viability, resulting in reduced chances of conception. Smoking can also cause damage to testicular function, male hypogonadism and sexual dysfunction, leading to male infertility. Smoking can cause tobacco amblyopia, and smoking in the elderly can cause macular degeneration, which may be due to atherosclerosis and an increased rate of platelet aggregation, contributing to local hypoxia. Recently, a study in the United States found that smoking in strong noise can cause permanent hearing loss, and even deafness.
Prevention: Avoiding smoking is the only effective means of prevention. The risk of lung cancer also decreases after quitting smoking; after 10 years of quitting, the risk of lung cancer is 50% of that of non-smokers. However, no matter how long one quits smoking, the risk of developing the disease does not reach the level of never smokers. Although smoking cessation is currently encouraged worldwide and there are more than 300 ways to stop smoking, there is little success.