Kids, don’t let the bullies in school ruin your life.

Being kicked or shoved intentionally by a schoolmate, being hurt by constant taunting — such instances of aggression, which psychologists refer to as “peer victimization” — can have lasting, harmful impacts.

A new study led by the University of Delaware and involving researchers from universities and hospitals in six states analyzed data collected from 4,297 students on their journey from fifth through tenth grade. The findings, published online in the medical journal Pediatrics, document the disturbing associations between peer victimization, depression and substance use.

“Students who experienced more frequent peer victimization in fifth grade were more likely to have greater symptoms of depression in seventh grade, and a greater likelihood of using alcohol, marijuana or tobacco in tenth grade,” said the study’s leader, Valerie Earnshaw, a social psychologist and assistant professor in UD’s College of Education and Human Development.

The research is based on student data collected between 2004 and 2011 for Healthy Passages, a study of risk and protective factors in adolescent health, sponsored by the Centers for Disease Control and Prevention. The students were from Birmingham, Alabama; Houston, Texas; and Los Angeles County, California. Forty-four percent were Latino, 29 percent were African American and 22 percent were white.

Although peer victimization is common during late childhood and early adolescence and appears to be associated with increased substance use, few studies have examined these associations longitudinally — meaning that data is gathered from the same subjects repeatedly over several years — or point to the psychological processes whereby peer victimization leads to substance use.

“We show that peer victimization in fifth grade has lasting effects on substance use five years later. We also show that depressive symptoms help to explain why peer victimization is associated with substance use, suggesting that youth may be self-medicating by using substances to relieve these negative emotions,” Earnshaw said.

Impacts and interventions

Peer victimization leads to substance use, and substance use can harm adolescent development with implications for health throughout the lifespan, Earnshaw said. Alcohol and marijuana use may interfere with brain development and can lead to injuries. Tobacco use may lead to respiratory illness, cancer and early death.

“Youth who develop substance use disorders are at risk of many mental and physical illnesses throughout life,” Earnshaw said. “So, the substance use that results from peer victimization can affect young people throughout their lives.”

Among the study’s findings, boys, sexual minority youth and youth living with chronic illness reported more frequent peer victimization in fifth grade. Age, obesity, race/ethnicity, household educational achievement and family income were not related to more frequent peer victimization.

Twenty-four percent of tenth graders in the study reported recent alcohol use, 15.2 percent reported marijuana use, and 11.7 percent reported tobacco use. Sexual minority status was more strongly related to alcohol use among girls than boys; it was also related to marijuana and tobacco use among girls but not boys.

Earnshaw used structural equation modeling — a form of statistical analysis — to examine the multiple variables across time and to test if there were relationships among them. She started working with the data in summer 2015 and finalized the model in fall 2016 in her office in UD’s Alison Hall.

An expert in stigma research, Earnshaw wants to understand why people treat other people poorly and how this poor treatment leads to poor health, including through substance use behaviors. She hopes this latest study will enlighten pediatricians, teachers, parents — anyone in a position to help students facing peer aggression.

“We urge pediatricians to screen youth for peer victimization, symptoms of depression and substance use,” says Earnshaw. “These doctors can offer counsel to youth and recommendations to parents and youth for approaching teachers and school staff for support. Moreover, youth experiencing depressive symptoms and substance use should be offered treatment when needed.”

The research team’s messages also extend to teachers.

“Peer victimization really matters, and we need to take it seriously — this echoes the messages educators already have been receiving,” Earnshaw says. “This study gives some additional evidence as to why it’s important to intervene. It also may give teachers insight into why students are depressed or using substances in middle and high school.”

The Agency for Healthcare Research and Quality supported Earnshaw’s work on the study.

Her co-authors include Marc N. Elliott from RAND Corporation, Sari L. Reisner from Boston Children’s Hospital, Harvard Medical School, Harvard T.H. Chan School of Public Health, and The Fenway Institute, Sylvie Mrug from the University of Alabama at Birmingham, Michael Windle from Emory University, Susan Tortolero Emery and Melissa F. Peskin, both from the University of Texas Health Science Center at Houston School of Public Health, and Mark A. Schuster from Boston Children’s Hospital and Harvard Medical School.