New study may broaden the picture of the consequences of childhood adversity

Several previous studies have shown that people who have experienced various types of adverse childhood experiences have a higher risk of suffering from psychiatric illness later in life. Now, a new study from Karolinska Institutet, using a special type of twin research design, can confirm the link, show a clear dose-response relationship and at the same time broaden the picture. The researchers can now show that there are also significant genetic and environmental factors that play a role and contribute to mental illness.

The researchers used three different cohorts of the Swedish Twin Registry, comprising over 25,000 individuals. The twins' responded to a large web-based questionnaire and answered questions about different types of adverse childhood experiences including family violence, emotional abuse or neglect, physical neglect, physical abuse, sexual abuse, rape and hate crime. In addition, information about adult psychiatric disorders was obtained from the Swedish Patient Registry.

"These are of course very difficult questions to answer, but this is the best data source we have access to," says Hilda Björk Daníelsdóttir, a doctoral student at the University of Iceland and visiting doctoral student at the Institute of Environmental Medicine at Karolinska Institutet and the study's first author.

By identifying twin pairs who reported different experiences of abuse while growing up in the same family and then following those who later received a psychiatric diagnosis, the researchers have been able to sort out how much of the increased risk is due to the abuse itself and how much is due to genetics and environment.

"Most previous studies on the mental health effects of childhood adversity have not been able to take these things into account. Now we can show that the increased risk of mental health problems after adverse childhood experiences can be partly explained by factors shared by family members, such as genetic factors or factors in the childhood environment," says Hilda Björk Daníelsdóttir.

She argues that this finding should therefore lead to health care interventions addressing risk factors within the whole family, not just the affected child or children.

The more different types of childhood adversities individuals experienced, the higher the risk was of receiving a psychiatric diagnosis later in life. The researchers can also show that sexual abuse and rape in childhood as well as having experienced three or more types of adversities were the experiences most strongly linked to future mental health problems. This is something that is also important knowledge when treating vulnerable children and their families.

"I hope that our study can raise awareness of childhood circumstances as possible causes of psychiatric disorders in adulthood and how to best address them,' says Hilda Björk Daníelsdóttir.

The research was funded by the European Research Council, the Icelandic Research Center and the EU's Horizon 2020.