A U.S. study has identified Internet use, sleep, alcohol and coffee consumption as contributing factors to weight gain in adolescent girls.

Researchers surveyed more than 5000 girls between the ages of 14 and 21 years about their weekly habits during the past year.

Girls who spent more recreational time on the Internet were found to sleep significantly less and consume more alcohol.

While no relationship was found between coffee consumption and Internet use, researchers found that girls who drank more coffee got less sleep and tended also to consume more alcohol.

“These relationships are partly due to girls taking up more than one of these behaviours as they get older,” explained Catherine Berkey, who conducted the study with colleagues at the Harvard Medical School, Brigham & Women's Hospital, and Washington University.

Berkey identified e-mail, instant messaging (IM), social networking and Web surfing as online time-sinks for adolescent girls.

“Our research indicates that the rise in Internet use for recreational purposes -- including email, social networking [such as] Facebook, IM, MySpace, [and] surfing the web -- may be responsible for part of the weight increases,” she told iTnews.

“Girls in our study who did these the most tended to gain more weight over time,” she explained.

The findings come at a time when obesity has become a prevalent issue in countries like the U.S. and Australia, and are expected to apply not just to teenage girls in the U.S., but also to adolescent boys and Australian adolescents.

“Because energy balance is key to weight gain, and recent patterns of weight gain in adolescent boys has been similar to that seen in girls, we expect the effects would be similar, especially for time on the Internet and alcoholic beverage intake,” Berkey told iTnews.

“Given that patterns of weight gain in adolescence have been similar in Australia and the US over the past 20 years, we expect they would apply to Australian adolescents as well,” she said.

Berkey warned that the behaviours may go unnoticed as causes of gradual weight gain.

To help maintain a healthy body weight, she encourages adolescent girls to replace recreational Internet time with more sleep, and avoid alcoholic beverage consumption.