BACKGROUND Unhealthy behaviours often occur in combination. In this study the relationship between education and lifestyle, defined as a cluster of risk behaviours, has been analysed with the purpose to assess socio-economic changes in multiple risk behaviour over time.   
 METHODS Cross-sectional data from the Belgian Health Interview Surveys 1997, 2001 and 2004 were analysed. This study is restricted to persons aged ≥ 15 years with information on those health behaviours and education (n = 7431, n = 8142 and n = 7459, respectively). A lifestyle index was created based on the sum of the four unhealthy behaviours: smokers vs. non-smokers, risky versus non-risky alcohol use, sedentaryness vs. physically active and poor vs. healthy diet. The lifestyle index was dichotomized as low (0-2) vs. high (3-4). For the assessment of socio-economic inequalities in multiple risk behaviour, summary measures as Odds Ratio (OR) and Relative Index of Inequality (RII) were calculated using logistic regression, stratified by sex.   
 RESULTS Of the adult population, 7.5% combined three to four unhealthy behaviours. Lower educated men are the most at risk. Besides, the OR among men significantly increased from 1.6 in 2001 to 3.4 in 2004 (P = 0.029). The increase of the OR among women was less pronounced. The RII, on the other hand, did not show any gradient, neither for men nor for women.   
 CONCLUSION Multiple risk behaviour is more common among lower educated people. An increasing polarization in socio-economic inequalities is assessed from 2001 to 2004 among men. Therefore, health promotion programmes should focus on the lower socio-economic classes and target risk behaviours simultaneously.
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