The effect of smoking on the risk of lung cancer mortality for asbestos workers in Great Britain (1971-2005)

Our plain-English summary of The effect of smoking on the risk of lung cancer mortality for asbestos workers in Great Britain (1971-2005), by G. Frost, A. Darnton, A.H. Harding (The Annals of Occupational Hygiene, 2011).

The study

• Authors: G. Frost, A. Darnton, A.H. Harding
• Journal: The Annals of Occupational Hygiene
• Published: 2011;55(3):239-47
• Cited by: 46 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objectives: Workers in the asbestos industry tend to have high smoking rates compared to the general population. Both asbestos exposure and cigarette smoking are recognized risk factors for lung cancer mortality, but the exact nature of the interaction between the two remains uncertain. The aim of this study was to examine the effect of smoking and smoking cessation among asbestos workers in Great Britain (GB) and investigate the interaction between asbestos exposure and smoking.

Methods: The study population consisted of 98 912 asbestos workers recruited into the GB Asbestos Survey from 1971, followed-up to December 2005. Poisson regression was used to estimate relative risks of lung cancer mortality associated with smoking habits of the asbestos workers and to assess whether these effects differed within various categories of asbestos exposure. The interaction between asbestos exposure and smoking was examined using the Synergy (S) and Multiplicativity (V) indices, which test the hypotheses of additive and multiplicative interaction, respectively. The proportion of lung cancers among smokers attributable to the interaction of asbestos and smoking was also estimated.

Results: During 1 780 233 person-years of follow-up, there were 1878 deaths from lung cancer (12% of all deaths). Risk of lung cancer mortality increased with packs smoked per day, smoking duration, and total smoke exposure (pack-years). Asbestos workers who stopped smoking remained at increased risk of lung cancer mortality up to 40 years after smoking cessation compared to asbestos workers who never smoked. The effects of smoking and stopping smoking did not differ by duration of asbestos exposure, main occupation, age at first asbestos exposure, year of first exposure, or latency period. The interaction between asbestos exposure and smoking for asbestos workers was greater than additive [S 1.4, 95% confidence interval (CI) 1.2-1.6], and the multiplicative hypothesis could not be rejected (V 0.9, 95% CI 0.3-2.4). For those asbestos workers who smoked, an estimated 26% (95% CI 14-38%) of lung cancer deaths were attributable to the interaction of asbestos and smoking.

Conclusions: This study emphasizes the importance of smoking prevention and cessation among those who work in the asbestos industry.

In plain English

This cohort study followed 98,912 workers in the Great Britain Asbestos Survey from 1971 to the end of 2005. All had medical examinations because of regular work with asbestos, and most were men. There were 1,878 lung cancer deaths among 15,553 deaths. After adjustment for age, sex, calendar period, occupation and exposure length, current smokers had a relative risk of lung cancer death of 14.7 (95% CI 10.5–20.6) and former smokers 4.6 (95% CI 3.3–6.6), compared with never-smokers in the cohort. Risk rose with years smoked and with pack-years. For former smokers, risk fell with time since quitting. After 40 or more years it was not statistically significantly different from never-smokers (RR 1.5, 95% CI 0.8–2.8). The effects of smoking did not differ by the measures of asbestos exposure. No unexposed group existed, so the authors compared workers with under 10 years of exposure against those with 30 or more. The combined effect was greater than additive, and a multiplicative effect could not be rejected. Among current smokers with 30 or more years of exposure, an estimated 26% (95% CI 14–38%) of lung cancer deaths were attributed to the interaction. Fiber types were not recorded.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Cohort study of a national survey of asbestos workers, analysed with Poisson regression; interaction tested with synergy (S) and multiplicativity (V) indices
• Who was studied: 98,912 asbestos workers in Great Britain who had medical examinations because of regular work with asbestos. They were recruited into the GB Asbestos Survey from 1971 and followed to December 2005, for 1,780,233 person-years. 95% were male. Main occupations: removal work 56%, manufacturing 30%, insulation work 5%, other 9%.
• Exposure: Occupational asbestos exposure, measured only through proxies: length of exposure (stand-in for cumulative exposure) and main occupation (stand-in for type of asbestos). No fiber types were recorded. Smoking habits were taken from the survey questionnaires.
• Main results:
  • There were 15,553 deaths in total, of which 1,878 were from lung cancer.
  • Compared with never-smokers in the cohort, after adjustment for age, calendar period, sex, main occupation and length of asbestos exposure: current smokers RR 14.7 (95% CI 10.5–20.6); former smokers RR 4.6 (95% CI 3.3–6.6).
  • Starting to smoke before age 16 carried the greatest risk compared with never-smokers: RR 13.7 (95% CI 9.7–19.4).
  • Lung cancer risk increased with smoking duration and with total smoke exposure (pack-years).
  • Former smokers who stopped before age 30 still had a statistically significantly higher risk than never-smokers: RR 1.8 (95% CI 1.01–3.2).
  • Former smokers who had stopped for 40 or more years did not have a statistically significantly different risk from never-smokers: RR 1.5 (95% CI 0.8–2.8).
  • The effects of smoking did not differ significantly by the asbestos exposure variables.
  • Among never-smokers, those with high exposure (30 or more years) had a higher risk than those with low exposure (under 10 years), but this was not statistically significant: RR 1.6 (95% CI 0.6–4.2).
  • The synergy index was statistically significantly above 1, which is evidence against a purely additive effect: S 1.4 (95% CI 1.2–1.6).
  • The multiplicativity index did not differ significantly from 1, so a multiplicative interaction could not be rejected: V 0.9 (95% CI 0.3–2.4).
  • When exposure was defined by occupation instead (manufacturing as low, insulation as high), the indices were similar: S 1.7 (95% CI 1.4–2.1); V 0.9 (95% CI 0.4–2.3).
  • Among current smokers with high asbestos exposure, an estimated 26% (95% CI 14–38%) of lung cancer deaths were attributed to the interaction of asbestos and smoking. A further 68% were attributed to smoking only and 2% to asbestos only. These estimates are based on comparing high with low exposure, not with no exposure.
• The authors' conclusion: The authors concluded that there was evidence of an interaction between asbestos exposure and smoking, that a multiplicative interaction could not be rejected, and that the study emphasizes smoking prevention and cessation among asbestos industry workers.
• Limitations the authors state:
  • The survey lacked detailed exposure measurements and any information on the type of asbestos fibers.
  • Length of exposure was used as a proxy for cumulative exposure and does not capture differences in exposure intensity.
  • There was no unexposed comparison group, so low exposure was compared with high exposure. The authors note this may overstate the 'background' share and understate the shares due to asbestos, smoking and their interaction.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer.

Medical terms in this study, explained in our Lexicon: Lung Cancer, Asbestos Exposure, Relative Risk, Habit, Latency, confidence interval.

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