Adopted children are three times more likely to develop physical and mental health disabilities than kids raised by their biological parents, U.S. researchers found.

Nearly 45 percent of children age 12 to 17 who were adopted from foster care homes developed moderate to severe health problems, compared with 14 percent of all youth in the age group, according a report released Wednesday by the Federal Interagency Forum on Child and Family Statistics. The most common conditions were learning disabilities such as attention deficit hyperactivity disorder.

Almost 3 percent of children are adopted, or 1.8 million kids.