Nearly 19 million children in the United States have at least one parent with a substance use disorder, according to a new study published Monday in JAMA Pediatrics. And a significant number of those children have a parent whose addiction is moderate or severe as opposed to mild, the study finds.

The number amounts to 1 in 4 children with a parent who has addiction.

“I’m an addiction doc, and so I think about this issue all the time,” says Dr. Scott Hadland, chief of adolescent medicine at Massachusetts General Hospital, who wasn’t involved in the new study. “Even still, I was surprised at how high that percentage was. It’s just an enormous number of kids that are affected.”