Smoking
Smoking is, by far, the leading risk factor for lung cancer. Risk increases with both quantity and duration of smoking.(1) In 2004, the United States Surgeon General released a report addressing the harmful effects of smoking on health (The Health Consequences of Smoking: A Report of the Surgeon General). Included in the report were the following statements:
"The evidence is sufficient to infer a causal relationship between smoking and lung cancer."
"Smoking causes genetic changes in cells of the lung that ultimately lead to the development of lung cancer."
"Although charactersitics of cigarettes have changed during the last 50 years and yields of tar and nicotine have declined substantially...the risk of lung cancer in smokers has not declined."
There are more than 60 molecules in cigarette smoke that are thought to be carcinogenic in humans or laboratory animals.(3) Two carcinogens highly associated with lung cancer are benzo[a]pyrene and N-nitrosamine NNK. These molecules bind to DNA and proteins, forming adducts. The presence of adducts increases the chance of DNA mutation and interferes with the proper function of proteins. Learn more about DNA mutations. The presence of adducts is directly related to smoking status. Studies show that the level of adducts drops when a person quits smoking.(4)