Social class differences in lung cancer mortality: risk factor explanations using two Scottish cohort studies

Background The study investigated differences in lung cancer mortality risk between social classes. Methods Twenty years of mortality follow-up were analysed in 7052 men and 8354 women from the Renfrew/Paisley general population study and 4021 working men from the Collaborative study. Results More manual than non-manual men and women smoked, reported morning phlegm, had worse lung function and lived in more deprived areas. Lung cancer mortality rates were higher in manual than non-manual men and women. Significantly higher lung cancer mortality risks were seen for manual compared to non-manual workers when adjusting for age only and adjustment for smoking reduced these risks to 1.41 (95% CI: 1.12-1.77) for men in the Renfrew/Paisley study, 1.28 (95% CI:0.94-1.75) for women in the Renfrew/Paisley study and 1.43 (95% CI:1.02-2.01) for men in the Collaborative study. Adjustment for lung function, phlegm and deprivation category attenuated the risks which were of borderline significance for men in the Renfrew/Paisley study and non significant for women in the Renfrew/Paisley study and men in the Collaborative study. Adding extra socioeconomic variables, available in the Collaborative study only, reduced the difference between the manual and non-manual social classes completely. Conclusions There is a difference in lung cancer risk between social classes, in addition to the effect of smoking. This can be explained by poor lung health, deprivation and poor socioeconomic conditions throughout life. As well as anti-smoking measures, reducing socioeconomic inequalities and targeting individuals with poor lung function for help with smoking cessation could help reduce future lung cancer incidence and mortality.