A new study by researchers in public health at the University of Iceland and the Karolinska Institute in Stockholm shows that the effects of childhood trauma on the development of mental disorders in adulthood are independent of family-related factors, such as genetics and childhood environment. The findings are reported in the latest issue of the scientific journal JAMA Psychiatry.
Previous studies have revealed that individuals who have experienced various types of childhood trauma are at increased risk of developing mental disorders as adults. In order to shed further light on such risks, the group behind the research in JAMA Psychiatry decided to use data from the Swedish Twin Registry, containing responses from over 25,000 twins to various questions regarding childhood trauma. This includes physical and emotional neglect, mental, physical, and sexual abuse, rape, and hate crimes. Information on subsequent diagnoses of mental disorders was obtained from the Swedish National Patient Register.
"It is of course very difficult to answer these questions, but this is the best data set we have access to," says Hilda Björk Daníelsdóttir, a doctoral student in public health sciences at the University of Iceland and the first author of the article, who has been a visiting doctoral student at the Institute of Environmental Medicine at the Karolinska Institute in Sweden. Hilda is a member of Unnur Valdimarsdóttir research group. Unnur is professor in public health sciences, but she works at both the University of Iceland and the Karolinska Institute and has received prestigious grants for her research, including a sought-after grant from the European Research Council (ERC).
This dataset afforded the opportunity to identify those twins who grew up together but reported different experiences of childhood trauma, and study how they fared in adulthood. Based on this information, the scientists could assess how much of the increased risk of mental disorders in adulthood could be attributed to trauma, and how much to genetics and other childhood environmental factors.
"In very few previous studies on the long-term effects of childhood trauma on mental health has it been possible to account for these factors. However, our results show that the twin who experienced trauma in childhood was more likely to develop a mental disorder in adulthood compared to the twin who did not experience such trauma - thus, we were able to exclude the influence of genetics and other familial factors," says Hilda.
Furthermore, the results indicate that the more traumas experienced in childhood, the greater the risk of being diagnosed with mental illness later in life. The results also reveal that those who experienced sexual violence and rape, or three or more types of childhood traumas were most likely to struggle with mental disorders as adults. The researchers say that this is important information, especially for those working with children in vulnerable situations and their families
"I hope that the study opens people's eyes to the potential impact of childhood circumstances on mental disorders in adulthood and how best to tackle them," says Hilda.