Investigating the spatial variability in incidence of coronary heart disease in the Gazel cohort: the impact of area socioeconomic position and mediating role of risk factors.

STUDY OBJECTIVE The aim of the study was to improve understanding of the relationships between contextual socioeconomic characteristics and coronary heart disease (CHD) incidence in France. Several authors have suggested that CHD risk factors (diabetes, hypertension, cholesterol, overweight, tobacco consumption) may partly mediate associations between socioeconomic environmental variables and CHD. Studies have assessed the overall mediating role of CHD risk factors, but have never investigated the specific mediating role of each risk factor, not allowing their specific contribution to the area socioeconomic position-CHD association to be disentangled. DESIGN After assessing geographical variations in CHD incidence and socioeconomic environmental effects on CHD using a multilevel Cox model, the extent to which this contextual effect was mediated by each of the CHD risk factors was assessed. PARTICIPANTS Data of the French GAZEL cohort (n=19,808) were used. MAIN RESULTS After adjustment for several individual socioeconomic indicators, it was found, in men from highly urbanised environments, that CHD incidence increased with decreasing socioeconomic position of the residential environment. After individual-level adjustment, a higher risk of obesity, smoking and cholesterol was observed in the most deprived residential environments. When risk factors were introduced into the model, a modest decrease was observed in the magnitude of the association between the socioeconomic contextual variable and CHD. Risk factors that contributed most to the decrease of the association were smoking and cholesterol. CONCLUSIONS Classic risk factors, although some of them more than others, mediated a modest part of the association between area socioeconomic position and CHD.