A new study suggests that constant bullying prevents overweight children from exercising, and all the teasing can make it harder to shed the pounds as an adult.

About one out of every five children is chronically bullied. Overweight kids are targeted more frequently, often while in gym class or playing sports.

A bullied child will avoid situations in which he's teased the most. For overweight kids, this sets up a vicious cycle that makes it more difficult for them to lose weight.

Researchers surveyed 100 overweight or at-risk-of-being-overweight children between the ages of 8 and 18 and found that as bullying rates went up, 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," said study lead author Eric Storch of the University of Florida.

A negative attitude towards exercise can last a lifetime, making it more difficult for the child to lose weight and increasing the likelihood that they will become obese adults.

The researchers also linked bullying to depression, loneliness and anxiety, factors that can additionally lower activity rates.

But the effects of bullying can be offset by strong support from family, Storch said. The best thing parents and teachers can do is figure how to work around the problem so children can still get exercise, and doctors should take peer relations into account when assessing overweight children.

The study is detailed this month in the online edition of the Journal of Pediatric Psychology.

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