Lung Cancer Risk Factors

Reviewed by: HU Medical Review Board | Last reviewed: July 2020.

Researchers have identified several risk factors that increase a person’s risk of developing lung cancer. Some risk factors can be controlled, while others cannot.

Is smoking a risk factor?

Smoking causes about 90 percent of all lung cancers, including small cell lung cancer (SCLC) and non-small cell lung cancer (NSCLC). The enormous effect of cigarette smoking far outweighs all other factors leading to lung cancer. Plus, the risk increases the longer someone smokes and the more cigarettes smoked per day.1,2

Cigarette smoking was fairly rare in the U.S. before World War I. It is estimated that the average adult smoked fewer than 100 cigarettes per year in 1900. By the mid-1960s, that number rose to about 4,400 cigarettes per person per year. The number of diagnoses and deaths from lung cancer increased along with the increase in cigarette smoking.3

While there is also an increased risk for lung cancer with other forms of tobacco use, such as cigar and pipe smoking, the risk appears less than with cigarette smoking. The effects of smoking marijuana have not been studied as much, but signs of precancerous lesions have been found in people who smoke marijuana.3

While doctors know that vaping causes lung damage, they do not yet know if vaping causes lung cancer in the same way that cigarette smoking does.4

Does age play a role?

Like most cancers, lung cancer occurs more often in older people. Most lung cancers are diagnosed in people age 65 or older. The average age at diagnosis is 70. Very few people are diagnosed with lung cancer before age 45.5,6

Secondhand smoke exposure

Nonsmokers who live with a smoker are 20 percent to 30 percent more likely to develop lung cancer. Exposure to secondhand smoke causes approximately 7,330 lung cancer cases each year. Secondhand smoke has been linked to sudden infant death syndrome, heart disease, asthma, and lung problems and ear infections in children.7

Family history of lung cancer

Unfortunately, a family history of lung cancer puts you at higher risk for lung cancer too. One large analysis that looked at 41 studies found a nearly 2-fold increased risk for lung cancer in people with a family history of the disease. This increased risk was present for both smokers and nonsmokers.2,3

Diet and exercise as a risk factor

Research suggests that a diet rich in fruits and vegetables may lower the risk of lung cancer. However, doctors do not know whether nutrients found in fruits and vegetables protect the person, or if a person who eats more fruits and vegetables is making other choices that keep them healthier overall.2

People who exercise also experience lower rates of lung cancer. Just as with diet, doctors do not yet understand why.2

Exposure to radon and radiation

Radon is a colorless, tasteless, and odorless gas that is produced by decaying uranium. It occurs naturally in soil and rock, and seeps into buildings and mines through small cracks. About 1 in every 15 homes in the U.S. has radon exposure. Exposure to radon the second-leading cause of lung cancer. It is estimated that 15,000 to 20,000 deaths from lung cancer each year are due to radon exposure. Smokers who are exposed to radon have a much higher risk of developing lung cancer.1,2

Exposure to high doses of radiation increases the risk of developing lung cancer, something scientists found among survivors of the atomic bomb in Japan. Today, x-rays and CT scans are the most likely sources of radiation exposure in the U.S. though the risk is low, even for smokers.2

Exposure to workplace carcinogens

Carcinogens are substances that are known to cause cancer or increase the risk of developing cancer. Lung cancer can be caused by exposures to carcinogens in the workplace, including asbestos, uranium, tar, arsenic, chromium, nickel, diesel fumes, soot, and coke (a type of fuel).1,2

In addition, the risk of developing lung cancer is even greater for smokers who are exposed to occupational carcinogens. Nonsmokers who are exposed to asbestos are 5 times more likely to develop lung cancer than those who are not exposed to asbestos. Exposure to workplace carcinogens also increases the risk of death from lung cancer.1,2

Dangers of air pollution

Air pollution can contain many chemicals known to increase the risk for lung cancer. The effect of low levels of air pollution over time are hard to measure. However, studies from around the world have shown that higher levels of outdoor air pollution increase lung cancer risk and deaths due to lung cancer. Indoor air pollution can be equally dangerous, especially among people exposed long-term to unvented fumes from cooking and heating.2

Beta-carotene supplements in smokers

Several studies have shown an increased risk of lung cancer among smokers who use high doses of beta-carotene supplements long-term. In normal, healthy, nonsmokers, beta-carotene supplements show a beneficial effect. However, smokers taking beta-carotene have developed more lung cancer tumors than those not taking the supplement.8

Other diseases and lung cancer

People who have other forms of lung disease, such as COPD and asthma, have higher rates of lung cancer. Two more rare lung diseases, idiopathic pulmonary fibrosis (IPF) and systemic sclerosis (SSc), are also tied to lung cancer. People with HIV develop lung cancer at younger ages than other people with lung cancer.2

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