BOSTON (AP) ― NFL veterans who started playing tackle football before the age of 12 are more likely to have cognitive difficulties after their careers, according to a study published on Wednesday in the journal Neurology.

Researchers tested 42 former players on their short-term memory, mental flexibility and problem solving and found those who picked up the sport before they were 12 years old functioned about 20 percent worse. Both groups scored below average on many of the tests, according to Robert Stern of the Boston University School of Medicine.

“There is a known period of critical brain development that occurs around puberty. And if the brain is injured during that time, it may have both short-term and long-term consequences,” Stern told the Associated Press. “This study supports that idea that we need to protect the brains of our children while they’re going through this dramatic development period.”

The release of the study during Super Bowl week was a reminder for fans ― especially those who are also parents ― that the sport has bigger problems than deflated footballs.

For the study, NFL players were divided into two groups: those who played as young children, and those who did not. Those in the former group performed worse on the cognitive tests, such as being asked to recall words from a list they had learned 15 minutes earlier.

“The brain is the most critical organ in our body. It’s responsible for every aspect of thinking, feeling, moving, behaving; it’s responsible for who we are,” Stern said. “So the question is: Do we want to expose our children to anything that may have significant negative consequences for how that brain is going to work later in life?”

The difficulty faced by the former players, who reported an average of nearly 400 concussions each during their lifetimes, is separate from the problem of chronic traumatic encephalopathy, which can only be diagnosed after death.

Stern said the research does not lead to any simple solutions.

Among the limitations of the study, which he conducted with researcher Julie Stamm, were that it only looked at former NFL players; the conclusions cannot be generalized to a broader population. Youth sports also have many health benefits that need to be considered by policymakers, sports organizations and parents, Stern said.

It also looked back at people who played a long time ago; conditions could have gotten better as concussion education improved ― or worse, because athletes are getting bigger and faster. “There is a need for so many follow-up studies,” Stern said.

“The issue for me is one of science being balanced with logic,” he said.