Higher socio-economic status of parents may increase risk for bipolar disorder in the offspring

Background. There are conflicting data regarding the socio-economic risk factors for bipolar disorders. The aim of the present study was to explore the association between the socio-economic status of an individual or the parent and the risk for bipolar disorder. Method. Two Danish registers were merged. From the data source, we extracted those born in 1960 or later, and those with a first-ever admission to, or contact with, Danish psychiatric facilities during 1981-1998 with a diagnosis of bipolar disorder. Fifty time-matched controls per case were chosen by the incidence-density sampling method. Effects of marital status, occupation, education, income, and wealth, of both subjects and the parents, were estimated using conditional logistic regression. Results. A total of 947 cases were matched to 47 350 controls. Those at high risk of bipolar disorders were: single subjects, those in receipt of social assistance, pension or sickness payments, unemployed, subjects with a shorter educational history, and subjects with lower income. Conversely, parental higher education and higher level of paternal wealth were associated with increased risk. These associations remained significant after adjustment for gender, family history of psychiatric diagnoses, and other socio-economic variables, and are unlikely to be explained by known biases. Conclusions. The associations of lower socio-economic indices of subjects may be explained as a consequence of the disease. The association of higher socio-economic indices of parents may be explained by socio-economic achievement in the family of origin.