WASHINGTON (HealthDay News) -- Sodas and other sugar-sweetened drinks are the most common beverages American kids buy from school vending machines, concludes a Harvard School of Public Health study.

It also found that children who eat at fast-food restaurants are more likely to have sugar-sweetened drinks.

The study looked at daily vending machine purchases and fast-food restaurant orders for 1,500 students at 10 middle schools.

It found that 71 percent of the students reported buying sugar-sweetened beverages from school vending machines, including 68 percent who bought one to three vending machine products, and 79 percent who bought four or more items from a vending machine.

"The number of items youth purchases at school vending machines was directly associated with sugar-sweetened beverages and intake," the study authors wrote.

They also found that sugar-sweetened drinks were bought by more students than any other type of item. More than three times as many sugar-sweetened drinks were bought by the students than the next most popular drink, water.

Eating at fast-food restaurants was also directly associated with consumption of sugar-sweetened drinks.

"These findings suggest that school vending machines and fast-food restaurants make independent contributions to total (sugar-sweetened) beverage intake that increase with repeated exposure or use," the researchers wrote.