Risk factors of disability pensions – what will twin studies from Finland and Sweden add?

Abstract

Abstract Background Finland and Sweden have been forerunners to investigate social insurance in twin cohorts. Using twin cohorts to research disability pension (DP) has provided a unique possibility to control for genetic and environmental factors (i.e. familial confounding). This is important, since genetics is known to play an important role in many chronic diseases for DP such as low back pain (30%), depression (40%) and a moderate (35-48 %) role in DP. Furthermore, familial confounding can be expected to affect many risk factors, i.e. health and behavior related factors and is therefore of interest in the associations between risk factors and DP. Methods In twin cohort studies for DP, first, the twins are treated as singletons, and the effect of risk factors on the incidence of DP is analyzed by applying regression models. Second, analyzing twin pairs discordant for both outcome (DP) and risk factors provides a possibility to control for familial confounding. This co-twin-control design is a unique tool, includes investigation whether twins who are exposed to a specific factor of interest more often are granted a DP than their non-exposed co-twins. Results Co-twin control design allows adjustment for familial confounding. Therefore, the results based on discordant twin pairs add to the epidemiological findings of unrelated subjects. Based on population-based twin cohort studies with long follow-up, indications exist that the familial confounding may have different role in the association between risk factors and DP depending on risk factors of interest but also on diagnosis group for DP. Conclusions Evidently the underlying medical condition is important, and the risk factors vary between diagnosis groups of DP. However, also familial factors play a role in process of sickness absence, in the transition from sickness absence to DP, and for DP. Therefore, need for early identification of risk factors and tailored interventions of prevention is emerged for public health.