The number of young children on prescription drugs for heartburn and other digestive problems jumped about 56 percent in recent years and researchers say obesity and overuse might be contributing to the surprising increase.

The surge was found in a Medco Health Solutions Inc. analysis released Thursday of U.S. prescription data for 2002-2006. It suggests that more than 2 million U.S. children 18 and under used drugs for digestive or gastrointestinal complaints last year.

"It's a signal that something's going on that we need to keep an eye on," said Dr. Robert Epstein, Medco's chief medical officer. "Whether it's parents getting their children diagnosed more frequently, or obesity," or other factors, "it bears further study," he said.

Researchers at Medco, a pharmacy benefits management company based in Franklin Lakes, N.J., analyzed prescription drug claims of more than 575,000 U.S. children.

They calculated that 557,259 infants and children up to age 4, or about 3 percent of youngsters in that age range, were taking these drugs last year. That's about a 56 percent increase from 2002.

There was a 31 percent increase among children aged 5 to 11, climbing to an estimated 551,653 children, or 2 percent in that age group in 2006, the analysis found.

Almost 1 million children aged 12 to 18 had prescriptions for the drugs last year, but that was up only 6 percent over 2002.

Acid-reducing drugs called proton pump inhibitors are the most common medicines prescribed for GI problems, the analysis said. They are used for acid reflux associated with heartburn, and a related condition called gastroesophageal reflux disease or GERD.

Some of these, including Prevacid, were approved for use in children during the study period, which likely also contributed to the prescription surge, said Dr. Benjamin Gold, an Emory University specialist in children's digestive diseases.

Heartburn is a common complication of being overweight and the surge happened during the nation's rising obesity epidemic, said Dr. Renee Jenkins, president-elect of the American Academy of Pediatrics. She noted that more than 10 percent of U.S. preschoolers and 30 percent of older children are considered overweight.

Gold said there's no hard data on how many children have acid reflux or GERD. But there's some evidence that the numbers are rising, and obesity could be playing a role, he said.

Heartburn and acid reflux are also extremely common in infants and young children. Many of them outgrow it and drug treatment often isn't needed, so the increase raises concerns about whether these drugs are sometimes being used unnecessarily, said Jenkins, a Howard University pediatrics professor.

While some children do require treatment including prescription drugs, many get better with no treatment or lifestyle changes such as smaller, more frequent meals or cutting down on fatty foods, she said.

Still, parents increasingly are demanding that doctors prescribe medicine for reflux, in part because of direct-to-consumer marketing, Gold said. But also, symptoms including frequent spitting up, irritability and stomach aches are troublesome and many parents prefer a quick fix, he said.

Gold said reflux drugs are generally safe but there is some evidence linking long-term use with an increased risk of infections including pneumonia and bowel inflammation.

To avoid overuse, Jenkins said parents should be willing to try non-drug approaches for treating reflux and other digestive problems in young children.