Cancer Research UK : Lung Cancer risk factors

Lung Cancer risk factors

This page presents information on lung cancer risk factors including, smoking, radon gas, industrial carcinogens, air pollution, family history , physical activity, previous cancer treatment, diet and alcohol and other factors

Smoking and lung cancer risk

Around 90% of lung cancers in men and 83% in women are estimated to be caused by the use of tobacco, either smoked directly or through indirect exposure1 (see smoking statistics for details of smoking prevalence in the UK and abroad).

Current smokers are 15 times more likely to die from lung cancer than life-long non-smokers.2 Risk of developing lung cancer is affected by level of consumption and duration of smoking.2

Compared with non-smokers, those who smoke between 1-14 cigarettes a day have eight times the risk of dying from lung cancer and those who smoke 25 or more cigarettes a day have 25 times the risk. However, risk is far more dependent on duration of smoking than consumption: smoking one pack of cigarettes a day for 20 years may be as much as 16 times more hazardous than smoking one pack a day for 10 years.3, 4.

There is also evidence that starting to smoke at a young age carries additional risks of lung damage.5

Smoking cessation has very significant health benefits even for people who have been smoking for many years.

A lifelong male smoker has a cumulative risk of 15.9% for developing lung cancer by age 75. For men who cease smoking at ages 60, 50, 40 and 30 years, their cumulative risk of dying from lung cancer falls to 9.9%, 6.0%, 3.0% and 1.7% respectively (Figure 4.1).6

Figure 4.1: Effects of stopping smoking at various ages on the cumulative risk (%) of death from lung cancer by age 75 for men

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Smoking cessation has the same health benefits for women with the cumulative risk of dying from lung cancer up to age 75 being 9.5% for life-long smokers, and falling to 5.3% and 2.2% for women who stopped smoking around age 60 and 50 respectively.

Data from other European countries support these results leading to the conclusion that giving up smoking in middle age avoids most of the subsequent risk of lung cancer.7

Studies in Europe and China have reported that exposure to Environmental Tobacco Smoke (ETS) at work may increase the risk of lung cancer by 65–80%.8,9 Exposure to ETS at home during childhood carries even higher risks, while non-smoking adults who live with smokers have been shown to have a 27% increased risk.8-10

Radon gas and lung cancer risk

Radon is considered to be the second most important cause of lung cancer after tobacco. A naturally occurring radioactive gas, radon is a known human carcinogen and increased risks of lung cancer were first observed in uranium miners with high radon exposure levels.11,12

Radon can also accumulate in homes and other buildings at much lower levels. 13 Some of the highest natural levels in the UK have been found in the southwest, but levels well above average have been found in other parts of the UK.

A study of indoor radon exposure estimated that it may be responsible for 9% of lung cancers in European countries.14

Exposure to radon multiplies the risk of lung cancer for both smokers and non-smokers by the same amount but its effect is much greater for smokers as their risk of lung cancer is already much higher. For example, at an indoor concentration of 800 Becquerels (Bq)/m³, the absolute risk of lung cancer by age 75 among non-smokers was an estimated 0.93%, while for smokers it was 21.6%.14

The average indoor radon concentration in Europe is estimated as 59 Bq/m³.

Industrial exposure and lung cancer risk

Several industrial carcinogens, for example, arsenic and polycyclic hydrocarbons as well as some occupations including non-ferrous metal production and painting, have been linked to lung cancer.15-18 There is evidence that heavy occupational exposure to diesel exhaust causes a small increase in lung cancer risk19,20 and the large American prospective Agricultural Health Study Exposure suggests that exposure to herbicides and insecticides increases lung cancer risk.21,22

Occupational exposure to silica can result in silicosis with a small increased risk for lung cancer, but without silicosis there is no increased risk.23Occupational exposure to asbestos in the UK was shown to increase the risk of lung cancer, but not in central and eastern Europe.24

Air pollution and lung cancer risk

Outdoor air pollution is also thought to make a small contribution to the lung cancer burden.25 Evidence is strongest for an increased risk of lung cancer caused by exposure to nitrogen oxides, particularly exposure to traffic fumes.26-28 Nitrogen oxides are produced as a by-product of combustion. In urban areas, traffic fumes are the main source of outdoor exposure. Use of solid fuel in the home for cooking or heating has been associated with an increased risk.29,30

Family history and lung cancer risk

(see also Molecular biology and genetics section)

A family history of lung cancer in a first-degree relative is associated with a two-fold increased risk, independent of smoking.31 If both cancers are diagnosed before the age of 60, the risk ratio is almost five-fold.32

The association between family history and risk may be stronger in black individuals than white.33

Physical activity and lung cancer risk

A meta-analysis found that people who participated in higher levels of recreational physical activity have a lower risk of lung cancer.34 Since that analysis, results from the EPIC study showed a lower risk with sports in men and cycling in women but no associations with overall recreational or household physical activity.35

A second subsequent study did not show a link between physical activity and lung cancer risk.36 In two other studies, women who are current or ex-smokers and participated in high levels of physical activity had a reduced risk of lung cancer.37,38

Further research is needed to clarify the role of physical activity and lung cancer risk.

Previous cancer treatment and lung cancer risk

Treatment for Hodgkin’s lymphoma increases lung cancer risk by 2.6–7-fold. Risk ratios are higher in smokers than non-smokers and with radiotherapy compared to chemotherapy.39 Increased risk of lung cancer has also been shown after treatment for non-Hodgkin’s lymphoma,40 and up to 30 years after diagnosis with testicular cancer, which is linked to radiation to the chest as part of the treatment.41

Diet and alcohol and lung cancer risk

A diet rich in vegetables has been associated with a reduced risk of lung cancer,42-44 but the protective effect may be limited to smokers:45-48 however, evidence remains mixed.49

Higher fruit consumption has also been associated with a small reduction in risk.48 The role of dietary vitamin C is as yet unclear and there is a suggestion that it may be a marker for other protective dietary factors.50,51

A higher intake of beta-cryptoxanthin may be associated with a reduced risk.50 Both vitamin C and beta-cryptoxanthin are found in brightly coloured fruit. Conversely, two randomised controlled trials showed an increased risk of lung cancer with beta-carotene supplementation in smokers or those with exposure to asbestos.52,53 Higher intakes of selenium, copper and zinc have all been associated with a reduced risk.54,55

The close association between smoking and alcohol intake is a possible confounding factor in studies of lung cancer risk and alcohol and no strong link has been established.45,56-60

Other factors and lung cancer risk

Significant increases in risk of lung cancer have been reported in people with HIV and AIDS even after accounting for smoking,61,62 although one study showed an association in men only.63

People with antibodies to Chlamydia pneumoniae have a small increase in risk.64 Chlamydia pneumoniae is an infectious bacteria associated with a number of diseases including pneumonia. An increased risk of lung cancer has been shown in people with systemic lupus erythematosus,65 and Klinefelter syndrome66, in both cases less than two-fold.

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