Girls drink more and more soft drinks as they get older, and their risk of becoming overweight may follow suit, new research suggests.

In a study that followed nearly 2,400 U.S. girls for 10 years, researchers found that, on average, girls’ consumption of regular soda rose two- to three-fold between the ages of 9 and 19.

And as soda intake climbed, so did girls’ daily calories and body mass index (BMI) - a measure of weight in relation to height.

Over the past several decades, U.S. children have steadily replaced beverages like milk with soft drinks and other sugary liquids. Many experts believe that this trend is partly to blame for the simultaneous increase in childhood BMI and obesity.

The new findings, published in the Journal of Pediatrics, are based on data from a federal study that followed white and African-American girls from different U.S. regions for 10 years.

Between the ages of 9 and 19, the girls’ average daily soda intake climbed steadily, while their milk intake went in the opposite direction. And unlike milk, fruit juice and other drinks, soda was related to girls’ BMI.

“We found that even when adjusting for overall caloric intake from all sources…soda intake was associated with weight gain,” lead study author Dr. Ruth H. Striegel-Moore, of Wesleyan University in Middletown, Connecticut, told Reuters Health.

The effect was modest, she said, but still important, given the growing problem of childhood obesity and the fact that soft drinks have no nutritional value beyond calories.

The drop-off in milk consumption in this study has also been seen in past research. Striegel-Moore said she believes this may be partly due to teenagers’ habit of skipping breakfast, a meal that has traditionally included milk and juice.

She noted that older adolescents also have more freedom to feast on fast food when they want, which may bump up their soda intake.

Striegel-Moore suggested that parents try to get their kids to eat a healthy breakfast - which includes milk or calcium-fortified juice - and limit outings to fast food restaurants. If the family does go out for a burger and fries, don’t “supersize” the soda, she advised.

Parents should also encourage their kids to use water, rather than sugar-laden drinks, as a thirst quencher, she added.

A number of large school districts have banned the sale of soft drinks in school vending machines and cafeterias, and Striegel-Moore said that others should do the same. But they could also do more, she noted, to encourage more healthful choices, such as low-fat milk and real fruit or vegetable juices, as opposed to fruit-flavored drinks.

One way to cut empty liquid calories, according to the researcher, could be to make water more available and palatable - school water fountains are often broken or not very clean.

SOURCE: Journal of Pediatrics, February 2006.