A study of Western Australian asbestos workers has revealed that those who smoked were at an increased risk of developing lung cancer for up to 20 years after quitting, compared with workers who had never smoked.
A team of researchers from the University of Western Australia led by Dr Alison Reid, examined the smoking habits of nearly 3000 former Wittenoom miners and millers – more than 40 per cent of the workforce – from 1979 to 2000. In that time, 138 of the workers taking part in the study were diagnosed with lung cancer.
The research team used a specially designed computer program to determine the risk of getting lung cancer as time past since first exposure to asbestos and quitting smoking.
They found that people who still smoked and had been exposed to asbestos had the highest risk of developing the cancer. But for those who no longer smoked, this risk remained elevated for 20 years or more after quitting.
And the risk of lung cancer in people who had stopped smoking for six years or less was 22 times greater than those who never smoked.
The study also found:
People who smoked 20 or more cigarettes a day had twice the risk of getting lung cancer as those who smoked less than 20 a day.
Workers who stopped smoking aged 50 years or older had an increased risk of lung cancer compared to those who stopped at younger ages, but this difference was not statistically significant.
After excluding those who developed lung cancer within three years of stopping smoking, the risk of lung cancer in former smokers who had stopped for six years or less was reduced, but was still large compared to those who had stopped for six years or longer.
Dr Reid’s team suggested that the risk of lung cancer in those who had stopped smoking for less than six years could be partly explained as smokers taking up the habit again.
Another explanation could be that “social stigma” led some workers to describe themselves as non-smokers when, in fact, they still smoked.
The study concluded that the 20-year “risk convergence” among people exposed to both asbestos and tobacco “may be due to the slower clearance of asbestos fibres from the lungs of smokers, especially those with impaired airway function”.
“Many previous researchers, including us, examining this issue have supported the hypothesis that the interaction between smoking and asbestos is multiplicative, in that asbestos increases the risk in proportion to the effect of smoking,” the study found.
The research team has emphasised the importance of smoking prevention and quit programs for the Wittenoom cohort. The study was published in the international journal, Occupational and Environmental Medicine.
By Catherine Madden