In the past, when researchers have surveyed students at one point in time, children and teens who were being bullied tended to score lower on measures of physical and mental health.
But few studies have examined whether the possible effects of bullying accumulate over the years, the researchers write in the journal Pediatrics.
They analyzed data from the Healthy Passages study, which surveyed students in Alabama, California and Texas about how much bullying they experienced and evaluated their physical and mental health.
Overall, 4,297 students completed the surveys in fifth, seventh and 10th grades.
The researchers found that about a third of the students had been regularly bullied at some point during the course of the study.
Generally, those who had been bullied in the past scored better on measures of physical and mental health, compared to those who were currently being bullied. Teens who were bullied throughout their school career scored the worst.
For example, about seven percent of 10th grade students who had never been bullied scored low on mental health measures. That compared to 12 percent who had been bullied in the past, 31 percent who were currently being bullied and almost 45 percent of those who underwent persistent bullying.
About eight percent of 10th grade students who were never bullied had poor physical health, compared to 12 percent of those who were bullied in the past, 26 percent who were currently being bullied and 22 percent who were continuously bullied.
Poor mental health included traits such as being sad, afraid and angry, according to Bogart. Poor physical health included limitations like not being able to walk far and not being able to pick up heavy objects.
"I think one key thing to take from this is that any adult that has any contact with children . . . (should) know what the signs of bullying might be," Bogart said. "This study tells us some of them, but not all of them."
"There are physical signs, but they're not always physical," she said.
For example, one non-physical sign that a young person is being bullied is that the child doesn't want to go to school.
Bogart also said it's important for parents to know if their child falls into one of the groups at high risk for bullying. Those groups include children with physical disabilities, those who are overweight and obese and those who are lesbian, gay, bisexual or questioning.
"I think this says - especially for parents - to be really attuned to what's going on in their kids' lives by paying attention, knowing what's going on during the school day and being aware so they'll notice changes like these," she said.
What career will your child have when he grows up? Take our quiz to find out!
Image: Bullied girl, via Shutterstock