The study was based on interviews with children in the Denver area and central New Jersey, without confirmation from parents or others. But the researchers and independent experts say the results are credible and raise awareness about a disturbing problem.
Overall, almost 8 percent of the third-graders, or 15 kids, said they had ever intentionally hurt themselves by cutting, burning or poking their skin with sharp objects, hitting themselves, or other methods. These children included 8-year-olds and some as young as 7. About two-thirds of the children had done it more than once.
"It's unfortunately probably more common than we want to think," said lead researcher Benjamin Hankin, an associate psychology professor at the University of Denver.
The study involved 665 kids, including 197 third-graders, and was published online Monday in the journal Pediatrics. The researchers had local schools send letters to families requesting that their children participate in the study. About two-thirds of families agreed; there were no differences among those who chose not to participate that might skew the results, Harkin said.
Many kids, even the youngest ones, find that causing physical pain helps them cope with emotional stress, Hankin said. Some researchers believe physical pain releases feel-good hormones called endorphins that can be calming.
Family strife, troubles in school and bullying are among reasons some kids hurt themselves; details on what caused the behavior among the study kids wasn't included in the published report.
Among older children studied, 4 percent of sixth-graders and almost 13 percent of ninth-graders said they had self-injured -- rates consistent with those seen in other studies.
The rate among third-graders echoes anecdotal reports from elementary school teachers, and similar numbers of older kids in other studies have said that they started before the age of 10, said Cornell University researcher Janis Whitlock. She was not involved in the current research.
Hankin said it's important for parents to know about self-injury and to have affected children evaluated by a pediatrician or mental health specialist.
Among older kids, those who hurt themselves are at risk for suicide attempts, although most self-injuring kids don't cause serious harm, said Wendy Lader, president of a St. Louis-based treatment center and clearinghouse for self-injury information.
Children with autism or a major psychiatric disorder that might feature self-injury were excluded from the study.
The children studied were racially and ethnically similar to the general U.S. population, but the study wasn't nationally representative. Similar results were found in both locations, which strengthened the findings, Hankin said.