Social cross-over in cardiovascular disease: context matters

The concept of the ‘social cross-over’ in cardiovascular disease (CVD) mortality was first described in 1978 by Marmot et al .1 By analysing mortality trends between 1931 and 1971 in England and Wales, Marmot et al found that the pattern of mortality from coronary heart disease changed over the years, from being more common among middle-class and upper-class men and women to being more common among working-class men and women.1 Underlying this change was a steep increase in CVD mortality among the working-class group starting in the 1950s for men and in the 1960s for women, concurrent with increases in smoking rates and dietary changes.1 In the study by Mallinson and colleagues, the authors describe the absence of a social cross-over in CVD mortality in Brazil.2 The study used cross-sectional data for 2010 from states at various degrees of economic development to proxy the changes in economic development experienced by high-income countries over time. Mallinson et al found no support for the social cross-over hypothesis. Instead, they found that education-based inequalities in CVD mortality were actually widest in the least developed states, meaning that CVD mortality was highest among the population with the lowest levels of educational attainment.2 Previous studies on the social cross-over have relied on longitudinal samples to examine how inequalities in CVD change over time. Mallinson et al instead leverage intracountry heterogeneity in social development. The use of cross-sectional data from one country has two important advantages: (1) uniformity of the vital statistics system across the country, which reduces inconsistencies in the quality of the data often present in cross-country comparisons, and (2) consistency of coding, one of the biggest issues in studies using historical data.2 The authors also addressed issues of variation in the quality of data across states and …