a1 Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden
a2 Department of Public Health, Faculty of Life Sciences, Hamburg University of Applied Sciences, Germany
a3 Department of Neuroscience, Child and Adolescent Psychiatry, University Hospital of Uppsala, Sweden
a4 National Board of Health and Welfare, Stockholm, Sweden
a5 Department of Women's and Children's Health, University of Uppsala, Sweden
a6 Centre for Health Equity Studies (CHESS), Karolinska Institutet/Stockholm University, Sweden
Background Parental characteristics influence the risk of offspring suicide. In this study we wanted to separate the hereditary from the environmental influence of such factors by comparing their effects in the adopted versus non-adopted.
Method A register study was conducted in a national cohort of 2 471 496 individuals born between 1946 and 1968, including 27 600 national adoptees, followed-up for suicide during 1987–2001. Cox regression was used to calculate hazard ratios (HR) for suicide of socio-economic indicators of the childhood household and biological parents' suicide, alcohol abuse and psychiatric morbidity separately in the adopted and non-adopted. Differences in effects were tested in interaction analyses.
Results Suicide and indicators of severe psychiatric disorder in the biological parents had similar effects on offspring suicide in the non-adopted and adopted (HR 1.5–2.3). Biological parents' alcohol abuse was a risk factor for suicide in the non-adopted group only (HR 1.8 v. 0.8, interaction effect: p=0.03). The effects of childhood household socio-economic factors on suicide were similar in adopted and non-adopted individuals, with growing up in a single parent household [HR 1.5 (95% confidence interval 1.4–1.5)] as the most important socio-economic risk factor for the non-adopted.
Conclusions The main familial effects of parental suicide and psychiatric morbidity on offspring suicide are not mediated by the post-natal environment or imitation, in contrast to effects of parental alcohol abuse that are primarily mediated by the post-natal environment. Social drift over generations because of psychiatric disorders does not seem likely to explain the association of socio-economic living conditions in childhood to suicide.
(Received April 02 2008)
(Revised May 19 2010)
(Accepted May 25 2010)
(Online publication July 07 2010)