Examining if there is a differential association between smoking and chronic disease across socioeconomic groups: pooling of data from 15 prospective cohort studies

Abstract

Background: For the same quantity of cigarettes smoked, relative to the more affluent, socioeconomically disadvantaged people have higher levels of smoking biomarkers. This may be ascribed to inhaling cigarette smoke more deeply and more frequently, and/or choosing higher tar-containing brands. We investigated if this increased tobacco load, as captured using cotinine, is associated with a greater risk of mortality in lower social groups.

Methods: We used Cox proportional hazards models stratified by socioeconomic position to calculate hazard ratios in a pooled sample of 15 English and Scottish prospective cohort studies (N=81476).

Results: During a mean (SD) follow-up of 10.3 (4.4) years, 8234 deaths occurred. Risk of total mortality (Hazards Ratio; 95% confidence interval) for smokers relative to never-smokers in the high (2.5; 2.1, 3.1), intermediate (2.1; 1.8, 2.4), and low (2.0; 1.9, 2.2) educational groups did not differ markedly (p for interaction=0.61). Similar findings emerged when using cause-specific outcomes, and occupational social class and housing tenure as socioeconomic indices.

Conclusion: Contrary to our hypothesis, we found no indication that disadvantaged people were more vulnerable to the impact of smoking on chronic disease mortality.