One twin was injured, the other was not. Their adult mental health varied.
Gemini is a treat for research psychologists. In a field constantly trying to unravel the effects of genetics, environment and life experience, they provide a natural controlled experiment as their paths diverge, subtly or dramatically, during adulthood.
Take Dennis and Douglas. In high school they looked so alike that friends told them apart by the cars they drove researchers said in a study of twins in Virginia. Most of their childhood experiences were shared – except that Dennis suffered an attempted sexual assault at the age of 13.
At the age of 18, Douglas married his high school sweetheart. He raised three children and became deeply religious. Dennis experienced short-term relationships and was divorced twice, falling into periods of despair after each divorce. In his 50s, Dennis had a history of severe depression, while his brother did not.
Why do twins, who share so many genetic and environmental factors, diverge in their experiences with mental illness as adults? On Wednesday, a team of researchers from the University of Iceland and the Karolinska Institutet in Sweden reported new findings about the role played by childhood trauma.
Their study of 25,252 adult twins in Sweden, published in JAMA PsychiatryResearch found that those who reported one or more childhood traumas – physical or emotional neglect or abuse, rape, sexual abuse, hate crimes or witnessing domestic violence – were 2.4 times more likely to be diagnosed with a psychiatric illness as those who did not.
If someone reported one or more of these experiences, the odds of being diagnosed with a mental illness rose sharply: by 52 percent for each additional negative experience. Of participants who reported three or more adverse experiences, almost a quarter had a psychiatric diagnosis of a depressive disorder, anxiety disorder, substance abuse disorder or stress disorder.
To disentangle the effects of these traumas from genetic or environmental factors, the researchers limited the pool to “discordant” pairs, with only one twin reporting childhood abuse. An analysis of 6,852 twins from these discordant pairs found that childhood abuse was still associated with mental illness in adults, although not as strongly as in the full cohort.
“These findings suggest a larger influence than I expected – that is, even after very tight control for shared genetic and environmental factors, we still observed a link between childhood adversity and poor mental health outcomes of adults,” says Hilda Bjork Danielsdottir, a PhD candidate at the University of Iceland and the first author of the study.
Twins who reported abuse were 1.2 times as likely to suffer from mental illness as the unaffected twin among identical twins, and 1.7 times as likely among fraternal twins. This effect was especially pronounced among subjects who reported experiencing sexual abuse, rape, and physical neglect.
Twins can diverge in their experiences with childhood trauma for many reasons, Ms. Danielsdottir said in an emailed response to questions. In 93 percent of the cases in which an individual subject reported a rape, the other twin had not experienced it.
Although domestic violence is “inherently familial,” she said, and was a shared experience more than half the time, twins can have different dynamics with their parents. For example, twins are more likely to confront a dysfunctional parent. Ms. Danielsdottir is an identical twin herself and said she “can confirm that we have different relationships with our parents (both good).”
More and more evidence
For decades, researchers have been collecting evidence linking childhood abuse and maltreatment to diseases later in life. A milestone 1998 survey among 9,508 adults found a direct correlation between child abuse and heart disease, cancer, lung disease and depression, often linked to behaviors such as smoking and alcohol consumption.
“That opened everything up,” says Dr. Jeremy Weleff, a psychiatrist at Yale University School of Medicine who has studied the effects of childhood adversity.
For decades, research had focused on biomedical models of mental illness, but the findings helped spark a shift toward examining the effects of childhood experiences, including social conditions such as racism, housing and poverty.
The two lines of research have been combined in research that maps the effect of trauma on the brain. a Report 2022 in Molecular Psychiatry, a journal in Nature, pointed to specific changes in “stress-sensitive brain areas” in people who were abused as children, and recommended that psychiatric diagnoses should add modifiers to reflect a history of trauma.
“These terrible things that happen to children and young people change the brain, they physically change the brain and in some ways cause mental illness,” said Dr. Weleff. “The mental illness that may have developed is more difficult to treat, or worse, or perhaps even fundamentally different.”
By ruling out the role of genetic factors, the new findings should dispel remaining doubt that childhood abuse leads to poorer mental health in adulthood, says Mark Bellis, a professor of public health at Liverpool John Moores University in Britain, who said wasn’t. involved in the study.
The findings add to “increasingly irrefutable evidence that it will cost us all far less if we invest in addressing” child abuse and neglect now, he added, rather than “continuing to pay for the epidemic harm.” ” cause downstream.