MONDAY, June 17, 2013 (HealthDay News) -- Being picked on by your brother or sister may seem like a normal part of growing up, but for some kids the bullying may be a source of depression and anxiety, a new study suggests.
Researchers found that among 3,600 kids in a U.S. survey, those who were pushed around by a sibling -- physically or verbally -- had higher scores on a measure of depression and anxiety symptoms.
"Historically, sibling aggression has been dismissed as normal," said lead researcher Corinna Jenkins Tucker, an associate professor of family studies at the University of New Hampshire. "It's been seen as benign, or even good for kids because it teaches them something about dealing with the world."
In general, parents and other adults tend to be more tolerant when siblings smack or taunt each other -- even if they would never condone it among peers.
But Tucker said her findings suggest that parents should not turn a blind eye to their kids' fights and teasing.
The study, reported online June 17 in the journal Pediatrics, has a number of limitations, Tucker acknowledged. One is that the children and parents were interviewed at one point in time, so it's not clear that the sibling aggression actually led to the poorer mental health.
"We can't say it's the cause," Tucker said. "But we can say there's a link."
An expert not involved in the study agreed that the one-time interview is an issue. "If you're feeling bad on the day you're interviewed, you may remember more instances of aggression," said William Copeland, an assistant professor of psychiatry and behavioral sciences at Duke University School of Medicine, who studies bullying and kids' mental health.
On top of that, it's tough to disentangle the effects of sibling bullying from other parts of a child's life. "We don't know, for example, how parents in the study responded to the aggression," Copeland said. "I'd like to know more about the family dynamics."
Still, he said, the findings shed some light on an issue that has gotten little attention compared with schoolyard bullying. "I think this shows us we need to address aggression no matter where it happens," Copeland said.
The findings are based on telephone interviews with nearly 3,600 children and their parents. Tucker's team used standard questionnaires to gauge the kids' levels of anger, depression and anxiety, and asked them about episodes of bullying -- from siblings and peers -- in the past year.
Overall, one-third of kids said they'd been the target of one type of sibling bullying: physical; verbal abuse, such as name-calling; or having their things stolen or purposely ruined.
In general, those kids had more mental health symptoms than those who reported no sibling bullying. And that was true, Tucker said, even when the researchers compensated for things such as bullying at school, parents' education levels and kids' exposure to family violence in general.
The findings leave a lot of unanswered questions, such as how severe and lasting any mental health symptoms might be. "Is this a short-term thing, or do these problems last?" Copeland asked.
It's also not clear whether it makes a difference if the bullying comes from a sibling who is much older or around the same age -- or whether it's between sisters, brothers or sisters and brothers, Tucker said.
But she and Copeland both said it's safe to assume that parents' reactions to their kids' aggression matters. "Let your kids know this is something you won't tolerate," Copeland said. Even if the bullying doesn't stop, he noted, kids may get a lot of comfort knowing they can turn to their parents for help.
"If there's no real escape for kids," he said, "that could make it a lot worse."
The American Academy of Pediatrics has advice on dealing with bullying.