According to the American Cancer Society, the Centers for Disease Control and Prevention, and the National Cancer Institute, smoking tobacco is the No. 1 cause of lung cancer in the United States. Smoking accounts for nearly 90 percent of all lung cancer cases, and those who smoke are 10 to 20 times more likely to develop lung cancer than nonsmokers. Even exposure to secondhand smoke causes 3,000 new cases of lung cancer each year among nonsmokers. According to the U.S. Environmental Protection Agency (EPA), smoking, radon, and secondhand smoke are the leading causes of lung cancer.

Smokers who have been exposed to asbestos are at an even higher risk of developing lung cancer, as their risk of contracting the disease increases by 50 to 84 times. In addition, those who smoke and have experienced asbestos exposure are at a greater risk of developing both asbestosis and mesothelioma. For more information about smoking and asbestos exposure, please see"Smoking, Asbestos Exposure, and Lung Cancer."

Risk Factors for Lung Cancer

Though it can be difficult for doctors to explain why some people develop lung cancer and others do not (especially among nonsmokers), certain risk factors can increase a person's chance of contracting lung cancer. Having a particular risk factor for lung cancer, or even several, does not mean the disease will develop. Likewise, it is possible for a person without any risk factors to develop the disease.

Some common risk factors for lung cancer include:

Smoking

Without a doubt, smoking is by far the biggest risk factor for developing all forms of lung cancer. Both cigar and pipe smoking are almost as likely to cause lung cancer as smoking cigarettes. Even smoking"light" or low-tar cigarettes does not reduce a smoker's risk of developing lung cancer. Lung cancer was a rare disease at the start of the twentieth century, but thanks to the advent of manufactured cigarettes, lung cancer is now the leading cause of cancer deaths in the United States.

Radon

According to the EPA, exposure to radon is the second leading cause of lung cancer in the United States, as well as the leading cause for nonsmokers. Radon is a naturally occurring radioactive gas that people cannot see, smell, or taste. Radon forms from the breakdown of uranium in soil and rocks, and certain areas of the country with natural uranium deposits are more likely to have elevated levels of radon inside homes (especially in basements). Outdoor levels of radon are so low that exposure does not pose a threat, but indoor levels can become increasingly concentrated and hazardous.

Smokers that have experienced exposure to radon have an even greater risk of developing lung cancer than smokers who have never been exposed to radon. The U.S. Surgeon General and the EPA highly encourage homeowners to test their residences for radon. Discounted radon testing kits are available through the National Safety Council by calling the council's Radon Hotline at (800) 767-7236.

Asbestos

Medical publications tracing back to the mid-1930s have undoubtedly proven that exposure to asbestos can cause lung cancer, as well as asbestosis (a progressive pulmonary disorder) and mesothelioma (the most common form of cancer caused by asbestos). A study published in 2001, which analyzed the excess risk of lung cancer due to occupational and environmental causes, found as much as 4 percent of all lung cancers annually diagnosed in the United States are attributable to asbestos exposure. In 1996, a study conducted by the National Institute for Occupational Safety and Health (NIOSH) analyzed 20 asbestos exposed cohort studies as a part of an assessment of occupational lung cancers. NIOSH found the combined relative risk of developing lung cancer among those exposed to asbestos was twice that of the unexposed population. In other words, people who are exposed to asbestos are twice as likely to develop lung cancer as those who have never been exposed.

Other Carcinogens in the Workplace

Aside from asbestos, there are other carcinogens found in workplaces across the country that are known to increase one's risk of developing lung cancer:

Radioactive ores, such as uranium
Inhalation of chemicals such as beryllium, cadmium, chloromethyl ethers, chromium compounds, coal products, mustard gas, nickel compounds, and vinyl chloride
Diesel exhaust

Arsenic

Researchers have found that high levels of arsenic in drinking water may increase a person's risk of contracting lung cancer. Among smokers, this factor is even more pronounced.

Other Carcinogenic Mineral Exposures

People affected by lung diseases such as silicosis and berylliosis, which are caused by the inhalation of certain minerals, have a higher risk of lung cancer. These lung diseases are usually observed within the mining industry.

Radiation Therapy on the Lungs

Those who have received radiation therapy to the chest for cancer treatment have an increased risk of lung cancer. This is especially true for those who smoke.

Genetic and Personal History of Lung Cancer

People who have already battled lung cancer have an elevated risk of developing lung cancer again. Siblings and children of those who have faced lung cancer may have a slightly higher chance of developing the disease. Medical professionals and researchers do not know how much of this risk may be attributable to genetic factors and how much may be due to shared exposures.

Environmental Pollution

An association has been observed between air pollution in cities and a slightly increased risk of lung cancer. It should be noted that this risk is far less than the risk caused by smoking cigarettes.

Diet

Researchers have been studying how a variety of foods may affect the risk of developing lung cancer. Studies have shown that eating a meat-based diet characteristically high in fat and cholesterol may increase a person's risk of lung cancer. Drinking an excess of alcohol may increase one's risk as well, but scientists are not sure whether the risk is more attributed to tobacco smoke since those who drink are more likely to smoke.

Some studies have shown that certain foods may help prevent lung cancer. Diets rich in fruits and vegetables, such as those followed by vegetarians and vegans, decrease cancer risk. Several studies have proven that vegetarians are 40 percent less likely to develop cancer than meat-eaters. More specifically, diets high in vitamin C, vitamin E, and selenium may protect against lung cancer as well. Carotenoids, such as beta-carotene (which can be found in sweet potatoes, carrots, and certain green vegetables), may lower the chance of lung cancer. However, taking beta-carotene supplements is not recommended since it could possibly increase the risk of lung cancer in smokers.

Other Possible Risk Factors

Scientists and researchers have been studying other plausible risk factors, such as personal history of certain lung diseases. Those with tuberculosis or bronchitis for many years may have a higher risk of contracting lung cancer.

Those who believe they may be at risk for developing lung cancer should contact their physician, who can suggest ways to reduce risk and help monitor health. The greatest way to prevent lung cancer is to abstain from smoking and avoid secondhand smoke. There are many resources available to smokers to help them quit smoking. The National Cancer Institute (NCI) offers information on topics such as ways to quit smoking, group support resources, NCI publications about quitting smoking, and how to partake in a study about methods to help smokers quit. Call NCI's Smoking Quitline at (877) 44U-QUIT. In addition, Smokefree.gov is a government website offering a guide to quit smoking and a variety of other resources.

Sources:

http://www.cancer.org/docroot/CRI/content/CRI_2_4_2x_What_Are_the_Risk_Factors_for_ Small_Cell_Lung_Cancer.asp?rnav=cri
http://www.cdc.gov/cancer/lung/basic_info/risk_factors.htm
http://www.epa.gov/radon/
http://www.nsc.org/resources/issues/radon/faq.aspx
http://www.cancer.net/portal/site/patient/menuitem.6067beb2271039bcfd7 48f68ee37a01d/?vgnextoid=1d27ea7105daa010VgnVCM100000ed730ad1RCRD&vgnextfmt=cancer
http://www.cancer.gov/cancertopics/factsheet/Tobacco/cancer
http://www.cancer.gov/cancertopics/wyntk/lung/page4
Haus, B., Razavi, H., Kuschner, W. Occupational and environmental causes of bronchogenic carcinoma. Curr. Opin.Pulm. Med: 7 (4), 220-225, 2001.
Steenland, K., Loomis, D., Shy, C., et al. Review of occupational lung carcinogens. Am. J. Ind. Med.: 29 (5), 474-490, 1996.