Overweight children and adolescents are contending with a problem that used to be rare in young people. They are at least twice as likely to have gallstones as their counterparts who are not overweight or obese.

Extremely obese children were 6 times as likely to have gallstone disease, according to the study that appeared in the Journal of Pediatric Gastroenterology and Nutrition. Latino children had the highest risk of developing the condition. Previous research has found that Latino adults also have the highest risk of gallstones.

An estimated 20 million adults in the U.S. have gallstones. Until now, they were thought to be rare among children.

Lead author Corinna Koebnick, a researcher at the Kaiser Permanente Southern California Department of Research and Evaluation, decided to examine rates of gallstones after hearing from pediatricians that the number of cases was increasing in overweight children.

“It is surprising to see these kind of associations already in children you would expect in adults,” Koebnick said. Adults, she added, have likely been obese or unhealthy for longer than children.

Gallstones can cause reoccurring abdominal pain and nausea. They may also block the passage of bile into the intestine and cause severe internal damage. Left untreated, gallstones can be fatal.

Girls were six to eight times as likely as boys in the same weight group to develop gallstones. The study can’t explain the difference, Koebnick said, but exposure to estrogen increases the chance of gallstone disease.

Moderately obese girls taking birth control pills were 2.5 times more likely to get gallstones than moderately obese girls not using the pill, the study found.

While gallstones can be serious, Koebnick said, they still aren’t common in children. Despite the increase among the overweight and obese, only .1 percent of youth surveyed had gallstones. That makes it difficult to study the disease.

Kaiser’s electronic health records gave researchers enough data to notice the trends, Koebnick said. They looked at the health records of slightly more than 500,000 children aged 10-19 in Southern California who were members of Kaiser Permanente Southern California between 2007 and 2009.

This study is a part of an effort to better understand and manage childhood obesity. Slightly more than seven percent of boys and 5.5 percent of girls under the age of 20 years are extremely obese, according to the Kaiser Permanente Southern California Children’s Health Study.

“We can see that kids are getting heavier, with the shift from obesity to extreme obesity,” Koebnick said. “We don’t really know where this will go.”