Does a population-based multi-factorial lifestyle intervention increase social inequality in smoking? The Inter99 study

Introduction: The social inequality in smoking in the Western countries has been increasing. It has been suggested that the most important strategy to reduce health inequalities related to socio economic status (SEP) is to promote smoking cessation in persons with low SEP. One could fear that a smoking cessation intervention might benefit smokers with high SEP more, and thereby increase the social inequality in smoking. We wanted to investigate whether the effect differed across SEP. Methods: The study was an individual multi-factorial lifestyle intervention study with a control group, Inter99 (1999-2006), Copenhagen, Denmark. We included 1991 daily-smokers with self-reported information on education in the intervention group, and 1135 in the control group. Smokers in the intervention group were repeatedly offered individual life-style-counselling and group-based smoking cessation. We used generalised linear mixed models under the assumption of missing at random, including interaction term between intervention effect and SEP. Results: The gap in self-reported abstinence rates increased over time between persons with high and low education. Probability of abstinence was significantly higher in the intervention group than in the control group, at all follow-up-visits but the effect of the intervention changed over time. The differences in quit-rates across educational groups were not significantly different in the intervention than in the control group at any time. Conclusion: In this randomised population-based intervention study we found that smokers across all educational levels benefited from the anti-smoking intervention, and that the intervention did not increase the social inequality in smoking, as one could have feared.