Children who are bullied at school are more likely to avoid exercise and therefore have a greater chance of becoming overweight or obese, a US study has revealed.

The study suggests that kids who are bullied try to avoid situations where they have been picked on before, such as gym class and sports.

University of Florida researchers studied 100 overweight or at-risk-for-being-overweight children between the ages of 8 and 18 to find out how bullying affected their exercise.

Several measures were used to assess how much of a problem bullying was for children and determine whether they were exhibiting signs of depression, anxiety or even behavioral problems as a result.

About one-quarter of the children reported significant problems with bullies during the two weeks preceding the study.

The researchers also found links between bullying and depression, loneliness and anxiety, further explaining why their physical activity rates were low.

Lead researcher Eric Storch said: "We found that as rates of peer victimization among overweight kids went up, rates of physical activity went down.

"The problem clinically is if kids are avoiding PE class or playing sports because of fears of negative peer relationships, their health status is affected."

Eric Storch, University of Florida: "We found that as rates of peer victimization among overweight kids went up, rates of physical activity went down."

Bullying not only contributes to children avoiding situations where they could be subject to ridicule, such as sports or gym class, but also can lead to depressed feelings that keep children from wanting to take part in activities, the researchers say.

"When you think about it, it makes intuitive sense, when you consider the hallmark signs of depression - sadness, fatigue, lack of interest in things you used to like," Storch said.

"When kids are having a tough time with peers, and struggling with depression, then this can translate to reduced rates of physical activity."

Schools should create a zero-tolerance culture for bullying and perhaps provide gym teachers with training on how to recognize bullying and intervene, the researchers say.

Doctors should keep peer problems in mind when assessing overweight children and take not only a medical history of the child but also a social history, so they can pinpoint the underlying problem and devise a solution, according to Storch.

It's important to prevent the problem early before it gets worse, he explained.

The findings appear this month in the online edition of the Journal of Pediatric Psychology.