Children born at extremely low birth weight may face greater risk of bullying than their normal-sized peers and be more prone to suffer lasting effects from victimization, a Canadian study suggests.

Among adult survivors of childhood bullying, people who had been tiny infants appeared more likely than those born weighing 2,500 grams (5.5 pounds) or more to be depressed, anxious, antisocial, avoidant, and hyperactive or experience obsessive-compulsive or panic disorders, researchers report in Pediatrics.

"While bullying has detrimental, long-term effects on every child, adults who were extremely low birth weight babies may suffer more because of all the hardships they have to overcome throughout their lives," said lead study author Kimberly Day, a researcher at the Offord Centre for Child Studies at McMaster University in Hamilton, Ontario.

Infants weighing less than 1,000 grams (2.2 pounds) at birth are considered to be extremely low birth weight babies. Some die as infants, and those that do survive may have complications like chronic lung disease, cognitive delays, behavioral and emotional problems, physical disabilities and impaired vision or hearing.

"The same differences that make them more sensitive to the effects of bullying may also put them at greater risk for experiencing bullying," Day added by email.

To assess how birth weight influences the lasting effects of childhood bullying, Day and colleagues examined psychiatric disorders in adults at two points in time, between ages 22 and 36.

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More than half of the 275 participants dropped out after the first assessment, which was done by age 26.

Among those who completed both adult evaluations, the 84 low birth weight babies had weighed about 829 grams (1.8 pounds) on average when they were born, while the control group of 90 normal sized infants weighed about 3,400 grams (7.5 pounds).

At the first adult evaluation, researchers asked participants to recall how often they endured physical or verbal abuse before age 16 using a 10-point scale, with the lowest scores meaning little to no bullying and the highest results indicating routine victimization.

Participants who were tiny babies reported average bullying scores of about 5.1, compared with just 4.4 for those who arrived in the world at an ordinary size.

By age 26, researchers found that for each one-point increase in the victimization score, the adults who were too small at birth had 67 percent higher odds of depression, 36 percent greater likelihood of anxiety, 92 percent increased risk for antisocial behavior and a 39 percent higher chance of attention-deficit/hyperactivity disorder.

Between ages 29 and 36, a one-point increase in the original peer victimization score predicted 69 percent higher odds of panic disorder and a more than tripled risk of obsessive-compulsive disorder for the low birth weight babies.

For normal-weight infants, bullying predicted increased odds of antisocial problems at ages 22 to 26, the study found.

In addition to the high dropout rate, it's possible that some adult participants didn't have an accurate memory of how much they experienced bullying during childhood, the researchers note.

Improvements in neonatal care since the participants were born in the 1970s and 1980s might also mean the findings could be different for future generations of kids, the authors also point out.

It's also possible that children who were born at an extremely low birth weight might perceive childhood bullying differently than kids who were bigger babies, said Dr. Matthew Davis, a pediatrics researcher and deputy director of the Institute for Healthcare Policy and Innovation at the University of Michigan.

Medical challenges might also affect their long-term learning and socialization, and they might develop differently as teens and adults than children born at normal weight, Davis, who wasn't involved in the study, added by email.

"Being a victim of bullying behavior is bad for children's health, period," Davis added. "What this study reminds us is that childhood bullying can have long-term effects on mental health, well into adulthood - especially for individuals who were born at extremely low birth weight."