The researchers wanted to know if a common mental illness is distressing and impairing to a child or teenager at the moment, does it continue to impact after they go into adulthood, Copeland tells Shots.
"Most common chronic conditions happen in middle adulthood, with the exception of mental illness," says William Copeland, lead author of the study and an associate professor of psychiatry at Duke University School of Medicine.
But for mental illness, symptoms usually first appear in childhood, and have the biggest impact in terms of financial cost, mortality and other indicators – a term known as disease burden – on youths from 10 to 24 globally.
But there are also a lot of people who report mental health problems that are significantly impairing their lives but don't count as having a psychiatric disorder under standardized criteria for diagnosis, according to Copeland. This is no small group – as many as half of the patients who go to a doctor for psychiatric disorders do not meet the established criteria, he says.
This is no minor problem, says Copeland, "the vast majority of them aren't getting help at all because they don't meet threshold, but [the impact] is still significant enough that they need help down the road," Copeland says.
Of course, a bad environment growing up doesn't help, so Copeland and team also took into account factors such as an unstable, dysfunctional or poor family background and retested the data. The results still hold true.
It's important to understand that the data from the study is not necessarily people who think they have mental disorders, but a random sample who were tested as part of the study and shown to have these symptoms, says Daniel Klein, professor of clinical psychology at Stony Brook University. In some cases the symptoms are very mild, and people don't see themselves as having a mental disorder.
And that's a problem.
"As a society we're prone to think of childhood as a relatively carefree life, obviously with exceptions, and most of the mental disorders you think about are in adults, except ADHD and autism, but the whole gambit are there in childhood," says Klein, who was not part of the study.
"People are coming around to the notion that these [mental health] problems are significant and can have long term affects," says Copeland. "Kids continue to have problems in adulthood even if it's not psychiatric problems."
It's important that we make treatment and prevention programs accessible in childhood, Klein say. On that, "we're doing a terrible job."
An editorial in the same issue of JAMA Psychiatry echoed that thought. Ben Lahey, a professor of epidemiology at the University of Chicago, believes that we as a society don't invest enough in mental health treatment, especially when it comes to children and adolescents, to reduce the burden later in adulthood.
Lahey also points out an important missing part of the puzzle: "The paper, and several papers before it, all they establish is childhood disorders predict adult disorders, they can't tell us why. Correlation does not imply causation."