Both smoking and asbestos irritate the lungs. Smoking is a well-known trigger for lung cancer. Chronic exposure to smoke (smoking) causes as many as 90% of lung cancers.1

Chronic exposure to asbestos causes lung damage, too

Workers in ship building, former insulation manufacturers, and current insulation removal business can be exposed for decades at their jobs. This chronic asbestos exposure can lead to asbestosis in some people. People with asbestosis have so much scarring in their lungs that they are constantly short of breath.

In Great Britain, chronic asbestos exposure causes 2 of every 100 deaths from lung cancer.1

Higher rate of lung cancer in smokers with chronic exposure to asbestos

Two large studies examined whether smoking increased the rate of lung cancer in workers chronically exposed to asbestos.1, 2

Frost et al examined the records of 98,912 people chronically exposed to asbestos in Great Britain. 1,878 workers died of lung cancer (12%) during the study from 1971 to 2005. They grouped the workers by their number of years on the job with asbestos exposure. The workers exposed to asbestos for less than 10 years were classified as low asbestos exposure. The workers exposed to asbestos for 10 years to 30 years were classified as medium asbestos exposure and those with more than 30 years were classified as high asbestos exposure.

Many workers in this industry smoke and some of them have quit smoking. Frost and colleagues compared the rate of lung cancer among current smokers, former smokers, and those who never smoked.

The following graph shows the relative risk of lung cancer in workers who were chronically exposed to asbestos.

Chronic Asbestos Exposure

As expected, smokers had a higher rate of lung cancer across all groups of asbestos-exposed workers. Former smokers, i.e., those who had quit, had lower rates of lung cancer, although the difference did not reach statistical significance. Workers who had never smoked had the lowest levels of lung cancer.

The graph shows that quitting smoking may help workers who are exposed to chronic asbestos exposure.

Frost concluded that “an estimated 26% of lung cancer deaths were attributable to the interaction between asbestos and smoking.”1

The interaction between smoking and chronic asbestos exposure appeared to be more than just adding the effects of smoking and the effects of chronic asbestosis together. It would be like adding 9 for smoking and 2 for chronic asbestos exposure together and getting more than just 11, such as 14.

In the second study, Markowitz and colleagues2 assessed the health status of the lungs of 2,377 workers in the insulation businesses, including its manufacturing, installation, and removal. They reviewed their health records from 1981 through 2008.

Markowitz wrote that “asbestos exposure increased the rate ratio of lung cancer by 5.2 fold, smoking by 10.3-fold, and both by 28.4-fold.” Most of the workers (61%) had asbestosis—scarring in the lungs and shortness of breath. More insulators with asbestosis had lung cancer than insulators without asbestosis.

Smoking increases lung cancer rate in workers with asbestosis

Since both smoking and asbestos damages the lungs, Markowitz and colleagues compared the rate of lung cancer in the different groups of insulators and people with asbestos exposure from a large health study.2

Workers with asbestosis who also smoked had a higher rate of lung cancer than non-smoking workers with asbestosis.2

Quitting the smoking habit reduces risk of lung cancer by half.

Insulators who had quit smoking for at least 10 years cut their risk of lung cancer in half in the Markowitz’s study.2

Although some earlier studies did not see a significant drop in lung cancer risk,1 quitting smoking provides additional health benefits.

If you're interested in quitting your smoking habit, visit the government's SmokeFree site for tips and advice.

Does smoking increase the risk of mesothelioma?

Offemans and colleagues used the Netherlands Cohort study of 58,279 men. They looked for effects of smoking and asbestos exposure on the risk of developing mesothelioma.3

Offermans wrote “There was no significant interaction between asbestos and smoking”, which agreed with an earlier study.4