A Duke University study reveals the lasting effects of bullying on both victims and the bullies themselves.

Last week the New York Post reported on the suicide of a 13-year-old Staten Island boy who had been relentlessly bullied at his Catholic school.

Danny Fitzgerald’s parents posted his sad and touching letter on Facebook.

It’s another example of why bullying is not good for children — or for anyone.

What’s more, the deleterious effects are no longer confined to the playground. They continue long after students close the schoolyard gate, several studies say.

It turns out that not only do people being bullied suffer long-term emotional problems, but so do the bullies.

Read more: Tips on how to stop bullying in schools »

Dr. Andre Sourander, a professor of child psychiatry at the University of Turku in Finland, reported that children who are bullied in early childhood have an increased risk of depressive disorders and need psychiatric treatment later in life.

His study results were reported last year in the journal JAMA Psychiatry.

Focusing on children who were 8 years old and bullied frequently, the researchers realized these subjects were more likely to develop a psychiatric disorder that needed treatment as an adult, compared to kids who were not bullied.

Previous studies have found a link between bullying and a higher risk of mental health problems during childhood, such as low self-esteem, poor school performance, depression, and an increased risk for suicide, Sourander said. His study tracked children aged 8 to 29.

Thanks to a nationwide hospital register that includes all inpatient and outpatient mental health visits in Finland, the team could trace the mental health outcomes of those aged 16 to 29.

About 20 percent of those who were bullies as children had a mental health problem that needed medical treatment as a teen or young adult. This compares to the 23 percent of the kids who were bullied frequently and had sought help for a psychiatric problem before age 30.

The group that fared worst in terms of adult mental health were the children who were frequently bullies and were also bullied themselves. About 31 percent of these children had psychiatric problems that required treatment, as well as the highest rates of depression, anxiety disorders, schizophrenia, and substance abuse of all the groups in the study.

Read more: The four types of bullying »

It also seems peers may be worse than parents when it comes to the psychological effects of disparaging words and harassment.

A study published last year in The Lancet Psychiatry reported that children who were bullied by peers had significant mental health problems as adults — even more significant than children who were mistreated by their parents or caregivers.

In his study, Dieter Wolke, Ph.D., psychology professor at the University of Warwick in England, defined maltreatment as physical, sexual, or emotional abuse by an adult caretaker.

Bullying, in contrast, is repeated aggression by peers — such as verbal taunts, physical attacks, or social exclusion — carried out at least once a week.

Wolke’s research team followed two groups of children, one British and one American, into adulthood. The data on maltreatment and bullying in youth correlated to mental health problems in adulthood.

“The strength of our study is that we found similar findings on the effects of bullying on adult mental health in both cohorts, despite their differences in population,” Wolke said.

One in 3 U.S. children reports that they’ve been bullied at school, and about 1 in 7 reports online bullying.

“Being bullied is not a harmless rite of passage or an inevitable part of growing up; it has serious long-term consequences,” said Wolke, acknowledging that it is pervasive across cultures and socioeconomic groups.

Read more: U.S suicide rate increases, highest among young girls »

In the United Kingdom, about 16,000 children permanently stay home from school because they are routinely bullied, and their academic achievement suffers as a result.

Bullied children may also suffer from serious illness, inability to focus, poor social relationships, and even have trouble holding down a job as adults.

According to a Duke University study published in 2014 in the Proceedings of the National Academy of Sciences, while young adults show long-term ill effects of having been bullied in childhood, those who did the bullying might in some way be healthier than their peers.

The report is based on findings from the longitudinal Great Smoky Mountains Study, which started in 1993 and followed 1,420 children from western North Carolina. Researchers interviewed the participants as many as nine times.

The study was led by William Copeland, Ph.D., an associate professor of psychiatry and behavioral sciences at Duke University Medical Center in North Carolina.

This study is the first indication that being a bully might actually be protective. It measured blood levels of C-reactive protein (CRP) — a biomarker of chronic inflammation that’s been linked to cardiovascular risk and metabolic syndrome — over several points in time. CRP is a sign of stress on the body, Copeland said, and “a harbinger of health problems down the road.”

His findings were challenged by Catherine Bradshaw, deputy director of the Johns Hopkins Center for the Prevention of Youth Violence in Maryland. She cautioned against paying too much attention to the lower CRP levels in bullies. Rather than a health benefit, the lower CRP levels might just reflect a difference in the bullies’ underlying biology.

A 2013 study published in JAMA Psychiatry by researchers at Duke University found that both bullies and people who are bullied have an increased risk of depression, panic disorder, and behavioral, educational, and emotional problems.

A group of 1,420 children aged 9 to 16 were examined 4 to 6 times over several years to determine whether bullying could predict psychiatric problems or suicide. The researchers found that people who are bullied have a higher rate of agoraphobia (an anxiety disorder), generalized anxiety disorder, and panic disorder.

An earlier study of children who experienced violence at a young age found that childhood trauma not only affects a child psychologically, but that the structure of the brain is altered to affect future decision-making.

The Duke team said bullying can “be easily assessed and monitored by health professionals and school personnel.” The issues are complicated, but to do nothing is to throw away a substantial number of young lives.

Editor’s Note: This story was originally published on Feb. 20, 2013, and was updated by Roberta Alexander on August 16, 2016.