Abstract P078: Exploring Social Inequalities in Ischemic Stroke Incidence in Europe. The MORGAM Project Cohort Component
Authors: Ferrario Marco M , Veronesi Giovanni , Chambless Lloyd E , Kuulasmaa Kari , Soderberg Stefan , Salomaa Veikko , Pajak Andrzej , Amouyel Philippe , Arveiler Dominique , Drygas Wojciech , Ferrieres Jean , Hart Nigel , Jorgensen Torben , Malyutina Sofia , Peters Annette , Tamosiunas Abdonas , Tunstall-Pedoe Hugh , Cesana Giancarlo 
Published: July 2021

Aims.
To explore the magnitude of educational-class inequalities in ischemic stroke incidence in European populations, and to assess to what extent they can be explained by major risk factors.

Methods.
The MORGAM study comprised 45 cohorts from Nordic Countries (Finland, Denmark, Sweden), UK (Northern Ireland, Scotland), Central EU (France, Germany, Northern Italy) and East EU (Lithuania, Poland) and Russia. Only cohorts with both fatal and non-fatal ischemic strokes during follow-up (median 12 years, IQR 10-19 years) were included. Baseline data were collected adhering to MONICA-like procedures. Stroke subtype was attributed based on hospital records and death codes. We derived 3 educational classes from population-, sex- and birth year-specific tertiles of years of schooling. We used Poisson regression models to estimate the age-adjusted difference in event rates between the bottom and the top educational classes distribution (Slope Index of Inequality, SII) and the proportion of events to be redistributed to achieve equality in event rates among educational classes (Relative Concentration Index, RCI). We estimated the pooled age- and risk factors-adjusted hazard ratios for bottom to top education (Relative Index of Inequality, RII) from sex-specific Cox models with a dummy variable for each population . We also tested the hypothesis of homogeneity of inequalities across populations by adding population*education interaction terms. The contribution of risk factors to RII was measured by: (lnRII[RFadj]- lnRII[AGEadj]) / lnRII[AGEadj]

Results.
The cohorts included 66,052 CVD-free subjects aged 35-64 years (37,181 men) at baseline. In men, the age-adjusted inequalities in ischemic stroke rates (SIIs) were 125 events per 100,000 person-years in the Nordic Countries, 156 in the UK and 178 in Central EU; the RCIs were 6%, 13% and 21%, respectively. In women, an inverse gradient (higher rates among more educated subjects) was present in Northern Sweden; in the remaining populations, the SII (RCI) ranged between 4 (1%) in Northern Italy and 278 (23%) events in Germany. Age-adjusted pooled RIIs for bottom to top education were 1.7 (95%CI: 1.4-2.1) in men and 1.5 (1.2-1.9) in women, with some variability across populations (homogeneity test p-value=0.06 in men and 0.07 in women) and gender groups. Together, total- and HDL-cholesterol, systolic blood pressure, anti-hypertensive treatment, smoking and diabetes explained 26% of hazard excess in men, and 40% in women. Main contributors were smoking (13%) and systolic blood pressure (9%) in men; and systolic blood pressure (13%), HDL-cholesterol (12%) and smoking (11%) in women.

Conclusions.
Less educated men and women had a higher ischemic stroke incidence risk in most European populations; in men, such inequalities followed a clear North-South geographic gradient. Traditional risk factors accounted for a minor part of risk excess in men.