Children with mental health issues are more likely to have poor mental and physical health in their late teens and early 20s, and are at greater risk of social isolation, low educational attainment, financial difficulties and heavy substance use.

That's according to new research led by RCSI University of Medicine and Health Sciences, which examined a wide range of data from more than 5,000 children and young adults in Ireland.

The findings, published in JAMA Network Open, are drawn from the "Growing up in Ireland" study. The researchers from Ireland, the UK, and Australia followed trends of mental health throughout childhood (ages nine to 13) for 5,141 people.

The vast majority (72.5%) of participants whose data were analyzed reported no significant mental health difficulties, but more than 1,400 individuals appeared to have some type of mental health or behavioral issue across childhood.

"Mental health symptoms often come and go throughout childhood and adolescence, so we do not want to over-rely on symptom levels at one point in time. We decided to investigate children who had persistent reports of mental health symptoms, regardless of whether they met the criteria for an official diagnosis," said study lead author Dr. Niamh Dooley from the RCSI Department of Psychiatry.

The study looked at how these patterns of childhood mental health affected a range of outcomes in late adolescence and early 20s. The study took a broad approach to life outcomes, examining aspects such as Leaving Certificate results, social isolation and how often they used health services as young adults, poor physical health issues (e.g. obesity, sleep difficulties), heavy substance use (alcohol, smoking), and/or the young person's general feelings of well-being.

Importantly, the researchers also took different types of childhood symptoms into account, such as whether a child tended to internalize their symptoms (as in depression and anxiety), externalize their symptoms (as in hyperactivity and behavioral problems), or both.

The research found that children with externalizing symptoms are at increased risk of heavy substance use as young adults. Children with internalizing symptoms are at the highest risk of poor physical health in their late teens and early 20s.

"Our analysis shows that mental health problems in childhood are linked with a wide range of functional issues in adulthood, beyond the realms of mental health. And some groups were at particular risk for specific outcomes. For instance, females with persistent symptoms across childhood, particularly internalizing symptoms, had very high rates of poor physical health by young adulthood," said Dr. Dooley.

The data also showed that those who had mental health issues in childhood were as likely to encounter educational/economic difficulties in young adulthood as they were to face further mental health problems.

"Over 50% of children with mental health issues had at least one educational or economic difficulty by young adulthood, compared to around 30% of those without mental health issues in childhood," said Dr. Dooley.

The findings point to the need for better screening and treatment of mental health problems in childhood and adolescence, which may prevent problems later on in life, according to study co-author Professor Mary Cannon, who is RCSI Professor of Psychiatric Epidemiology and Youth Mental Health.

"Our study shows that mental health symptoms in childhood can cast a long-lasting shadow on adult life," said Professor Cannon. "If we understand more about which children in the general population are at greatest risk of poor outcomes, it will help to inform and improve early screening and approaches to support those children."

Professor Cannon is a member of a working group tasked with implementing the "Sharing the Vision" mental health policy recommendations, with a particular focus on improving transition of young people from child to adult mental health services.