Background Mortality is strongly correlated with socio-economic status (SES). Lifestyle factors impact on health and are also independently linked with SES, and thus may drive the mortality-SES associations. However, their relative individual and combined contributions to such inequalities have not been well quantified. We addressed this using nationally representative prospective data.

Methods Analyses were based on 6060 participants aged over 16 years in the 2003 Scottish Health Survey (60% response) providing data on cigarette smoking status, weekly alcohol intake, physical activity levels, diet (quality index) and body mass index (BMI; weight/[height]²), and consenting to linkage with mortality records (until 2008). Cox proportional hazards regression assessed the relative index of inequality (RII) in mortality by SES (occupational social class) and attenuation by lifestyle factors.

Results Mortality-SES patterns were clear (292 deaths; p<0.001) and did not differ by sex (p=0.212). The inequality across the social classes was more than twofold [age-adjusted RII HR=2.26; 95% CI 1.47 to 3.47]. Mutually adjusting for lifestyle factors reduced differences by 49% [1.65; 1.06 to 2.57], with the greatest individual impacts made by cigarette smoking (29%), diet (27%) and physical activity (20%); alcohol consumption and BMI had lesser effect.

Conclusions Around half of the SES patterning of mortality was explained by these lifestyle factors. Our findings provide valuable insight on the relative impact of individual lifestyle factors—essential for tackling socio-economic inequalities in health—highlighting the importance of promoting healthy eating and physical activity as well as further reducing smoking.