Life course socioeconomic position and the risk of cardiovascular events and all-cause mortality in a Norwegian twin study

Socioeconomic disadvantage throughout life is associated with an increased risk of cardiovascular diseases (CVD) and all-cause mortality. However, the extent to which common familial genetic and environmental factors explain this association is unclear. This study investigates family- and individual-specific effects on this association using twin data. Data from 21,051 twins were linked to census and registry data on 20 indicators of socioeconomic position (SEP) from 1960 to 1990, with follow-up on hospital discharges and causes of death until 2018. A graded item response model was used to aggregate SEP indicators into a linear scale, divided into quintiles. Hazard ratios were estimated using a mixed-effects Weibull proportional hazard regression model. At the familial level, higher SEP quintiles were associated with a lower risk of CVD events (HR = 0.51 for monozygotic [MZ] twins, HR = 0.56 for dizygotic [DZ] twins). Individual-specific effects showed hazard ratios of 0.80 for MZ twins and 0.73 for DZ twins. For all-cause mortality, familial risks for the top two quintiles were HR = 0.64 in MZ twins and HR = 0.61 in DZ twins, with individual-specific effects at HR = 0.71 in MZ twins and HR = 0.74 in DZ twins. The associations between life course SEP and both CVD and all-cause mortality are partly explained by shared familial factors from early life, with shared genetic factors having minimal additional influence.