What Twins Tell Us About Childhood Trauma and Adult Mental Health

In addition to outward appearances, twins raised in the same household share a great deal of genetic material and childhood experiences. So when the mental health of twins diverges radically in adulthood, research psychologists are intrigued. A New York Times article sheds light on a recent study providing strong new evidence that childhood trauma impacts adult mental health.

A team of researchers from the University of Iceland and Karolinska Institutet in Sweden set out to explore the impact of adverse childhood experiences (ACEs) on adult mental health. Their study, which sought to separate the role ACEs, genetics, and environmental factors play in mental health outcomes, was published in JAMA Psychiatry last week.

Using the Swedish Twin Registry, a data set involving 25,252 individuals, researchers discovered that “those who reported one or more trauma in childhood — physical or emotional neglect or abuse, rape, sexual abuse, hate crimes or witnessing domestic violence — were 2.4 times as likely to be diagnosed with a psychiatric illness as those who did not,” The New York Times reported.

For those who reported more than one of these traumatic experiences, the odds of being diagnosed with a mental illness shot up by 52 percent for each additional ACE. And nearly one in four adults who reported three or more adverse childhood experiences had “a psychiatric diagnosis of depressive disorder, anxiety disorder, substance abuse disorder or stress disorder” – far above the average in the general population.

What happens when only one twin experiences childhood trauma

To separate out ACEs from genetic or environmental factors – such as growing up in a neighborhood plagued by crime, or living in a household with a highly critical parent – the researchers focused on “discordant” pairs, where only twin experienced childhood harm. By analyzing over 6,800 twins from these discordant pairs, researchers discovered that childhood trauma was still linked with mental illness in adulthood, although not as strongly as in the entire group.

“These findings suggest greater influence than I expected — that is, even after very stringent control of shared genetic and environmental factors, we still observed an association between childhood adversity and poor adult mental health outcomes,” said lead study author Hilda Bjork Danielsdottir, a doctoral candidate at the University of Iceland.

An identical twin who was harmed in childhood was 1.2 times as likely to suffer from a mental health condition as the unaffected twin. In the case of fraternal twins, the twin who was traumatized was 1.7 times as likely to have a poor mental health outcome in adulthood.

Growing evidence links childhood trauma to adult mental ill health

For the past several decades, researchers have found evidence linking child abuse and maltreatment to illnesses later in life. One groundbreaking 1998 study of 9,508 adults found a “a direct correlation between childhood maltreatment and heart disease, cancer, lung disease and depression, often linked by behavior like smoking and alcohol use.”

But since correlation is not equal to causation, it has been hard to prove that the trauma alone caused problems with physical and mental health down the line. What if those individuals were merely genetically predisposed to physical or mental health conditions?

This new study helps answer those questions. By ruling out genetic factors, the study findings help erase any doubt that childhood trauma leads to worse adult mental health, said Mark Bellis, a professor of public health at Liverpool John Moores University in the U.K., who was unaffiliated with the study.

The new study’s findings add to the mountain of “increasingly irrefutable evidence that it is going to cost us all a lot less if we invest in tackling” childhood abuse and neglect now, said Bellis, rather than “continuing to pay for the epidemic levels of harm” they cause later in life.

Read the full article here.

Or read the research study at JAMA Psychiatry.

 

Barry, Ellen. “One Twin Was Hurt, the Other Was Not. As Adults, Their Mental Health Diverged.” The New York Times, 9 Mar 2024, https://www.nytimes.com/2024/03/06/health/one-twin-was-hurt-the-other-was-not-their-adult-mental-health-diverged.html.