Lung Cancer Encyclopedia 1: The Main Causes of Lung Cancer
Lung cancer is the cancer with the highest incidence and mortality of all malignancies. Over the past few decades, lung cancer has accounted for roughly one-fifth of all cancer-related deaths worldwide. In 2008, 28% of all cancer deaths in the United States were from lung cancer. China has the world's highest incidence and mortality of lung cancer; about one-third of the world's lung-cancer patients are in China.
China's high lung-cancer incidence is most closely tied to cigarettes, air pollution, and indoor air pollution from traditional cooking methods. China has 350 million smokers, about one-third of the world's total, which is the main reason its lung-cancer prevalence leads the world. More than 80% of lung-cancer cases are caused by smoking or secondhand smoke.
Smoking greatly shortens Chinese smokers' average life expectancy; smokers live on average more than ten years less than non-smokers. Besides lung cancer, they die more often from chronic obstructive pulmonary disease and cardiovascular and cerebrovascular disease. Of the 3,000-odd compounds in tobacco smoke, at least 50 are recognized carcinogens. These include organic compounds such as polycyclic aromatic hydrocarbons (PAHs), N-nitrosamines, and aromatic amines (e.g., benzene, acrylonitrile), as well as inorganic compounds like arsenic and acetaldehyde. Pipe and cigar smoking are even more harmful. Nicotine in tobacco is not itself carcinogenic, but it causes addiction to cigarettes. So to genuinely reduce lung-cancer incidence, quitting smoking is the most effective measure.
China's traditional cooking methods are one of the main causes of lung cancer among Chinese women. It has been reported that replacing open cooking fires with stoves fitted with ventilated chimneys in rural Yunnan reduces lung-cancer incidence by 40–45%. In Shanghai, women's lung-cancer incidence is linked to long exposure to cooking-oil fumes. Because Chinese cooking favors stir-frying in hot oil, the fumes released from rapeseed oil and soybean oil at high temperature condense into mutagenic compounds, and most Chinese women inhale these carcinogenic oil-particle fumes throughout their lives. In northeast China, indoor air pollution from coal burning for heating is also a major cause of lung cancer.
Like cigarettes, cooking-oil fumes are also an important trigger of chronic obstructive pulmonary disease and cardiovascular and cerebrovascular disease. So it is necessary to change traditional Chinese cooking methods and avoid stir-frying in hot oil. In fact, oils such as palm oil that need not be heated are also healthier. Installing range hoods with good ventilation in kitchens can reduce the incidence of lung cancer and chronic obstructive pulmonary disease.
In addition, PM2.5 has a major impact on China's lung-cancer mortality: PM2.5 accounts for 23.9% of lung-cancer deaths in China, far above the global level of 16.5%. This burden is worst in large cities. in large cities. According to Xia Guang, director of the Policy Research Center for Environment and Economy of China's Ministry of Environmental Protection, severe PM2.5 exceedances in large Chinese cities are related to: (1) destruction of vegetation around cities, increasing exposed topsoil and long-distance dust transport; (2) construction boom in urban fringes after city centers, raising dust; (3) pollutant emissions from industrial production and daily life, including coal-fired boilers, vehicle exhaust, cooking fumes, gas stations, and home-renovation volatiles; and (4) emissions from heavy chemical industry in neighboring cities—for example, neighboring cities contribute nearly one-quarter of Beijing's PM2.5.
Besides these three main causes, lung cancer is also thought to be related to the following factors:
First, the radioactive element radon. Radon is a colorless, odorless, radioactive noble gas at room temperature that can seep up through the earth's crust and accumulate indoors. People living in stone houses or with many stone furnishings are at higher risk of radon-induced cancer. In Sweden, people living in stone houses have a higher lung-cancer risk than those in wooden houses. In the United States, 6,000–36,000 lung-cancer cases each year are caused by indoor radon radiation. Radon exposure combined with smoking markedly increases lung-cancer risk.
Occupational respiratory carcinogens also cause lung cancer; workers in cement plants, metal mines, and coal mines have higher lung-cancer risk than the general population. Long-term asbestos exposure also raises risk; such workers are not only more prone to lung cancer but also to mesothelioma. Common asbestos products include textiles, cement, paper, wicks, ropes, flooring, roof tiles, water pipes, wallboard, fire suits, gaskets, and brake pads.
Dietary excess or deficiency also affects lung-cancer risk; high-fat, high-cholesterol diets and abdominal obesity raise risk. Eating more fresh vegetables and fruit lowers the risk of all lung-cancer types: those who eat the most fresh produce have a 40–50% lower risk of every lung-cancer type than those who eat the least, even among smokers. Some studies show that beta-carotene and retinol (vitamin A) significantly reduce lung-cancer risk.
In addition, chronic pulmonary inflammation, chronic obstructive pulmonary disease, pulmonary fibrosis, tuberculosis, and silicosis are also related to lung cancer. Tuberculosis is especially high-risk; a study in Shanghai found that about 9% of lung-cancer patients had previously been infected with tuberculosis.