Inequalities in non-communicable diseases: Indirect selection or social causation? (The Indi-Ineq study)

Non-communicable diseases (NCD) account for a major share of the disease burden in Norway and similar countries. NCDs vary between social groups and are largely determined by smoking, blood pressure, unhealthy food diet, inactivity, overweight, and alcohol. The project will investigate the impact underlying individual traits have for socioeconomic inequalities in NCD risk. Individual traits are more or less stable and may influence both socioeconomic position (SEP) and disease risk and give rise to associations between SEP and NCD through indirect selection over the life course. Social inequalities in health can in general be explained by two alternative mechanisms: social causation or selection. Selection is indirect when these associations comes about through individual traits with a distribution in the population, such as high cognitive ability, and not direct through clinical conditions (reverse causality). These traits can often be difficult to measure. Advanced welfare states have failed to eradicate inequalities in health. Indirect selection could be a reason because individuals are now expected to fine regulate their health behaviour constantly over a life-time. Cardiovascular diseases (CVD) will be a model for other NCDs, because the causal role of risk factors in CVD is known. In general, genetic factors are important for differences in health between individuals but not for differences at population level. Indirect selection may be a life-long process of amplification that only partially involves genetic factors. The project will take advantage of population based genotyped data from The North Trøndelag Health Survey (n=70,000) and Norwegian large-scale register linkage of family data (n=7,4 mill), and a linkage between the two. We will investigate if SEP and CVD is genetically linked, study the impact of individual heterogeneity and investigate the role of the extended family.

The project will investigate the impact underlying individual traits have for socioeconomic inequalities in non-communicable disease (NCD) risk. Individual traits are more or less stable and may influence both socioeconomic position (SEP) and disease risk and give rise to associations between SEP and NCD through indirect selection over the life course. Social inequalities in health can in general be explained by two alternative mechanisms: social causation or selection. Selection is indirect when these associations comes about through individual traits with a distribution in the population, such as high cognitive ability, and not direct through clinical conditions (reverse causality). These traits can often be difficult to measure (unobserved heterogeneity). Indirect selection has consequently been difficult to study, yet the influence may be profound. Advanced welfare states have failed to eradicate inequalities in health. Indirect selection could be a reason because individuals are now expected to fine regulate their health behaviour constantly over a life time. Cardiovascular risk factors account for a major share of the NCD burden. Cardiovascular diseases (CVD) will serve here as a model for other NCDs, because the causal role of risk factors in CVD is well established. They are mediated through individual behavior and socially patterned through the life course. In general, genetic factors are important for differences in health between individuals but not for differences at population level. Indirect selection may be a life-long process of amplification that only partially involves genetic factors. The project will take advantage of population based genotyped data from The North Trøndelag Health Survey (n=70,000) and Norwegian large-scale register linkage of family data (n=7,4 mill), and a linkage between the two. We will investigate if SEP and CVD is genetically linked, study the impact of individual heterogeneity and investigate the of the extended family.