BARBARA HOWARD: Well we've heard about concussions and NFL players, but what about children who play tackle football? A new study out today from Boston University's Chronic Traumatic Encephalopathy Center links kids under age 12 who play tackle football with mood and behavior problems later in life. In the studio to talk about these findings is Dr. Robert Stern, who helped lead that study. Thanks for being here, Dr. Stern.

STERN: Thanks for having me.

HOWARD: So who did you look at for this study?

STERN: We looked at a little over 200 former football players. They were people who only played up through high school, some people who only played up through college, and then some people who played all the way through the pros. They were all in adulthood, average age was 51.

HOWARD: And what did you find?

STERN: Well what we found was that folks who started playing tackle football before the age of 12, compared to the ones who started at 12 or older, had three times the odds of having depression as adults and two times the odds of having problems with behavioral regulation, being kind of out of control, and problems with apathy.

HOWARD: Is there a safe sport for people to enroll their children in?

STERN: Oh, sure. You know, kids need to participate in sports. And boy, do they need to exercise. With tackle football, playing the game involves hundreds of hits to the head every season. It's inherent in the game. Each one of those hits, the brain is moving rapidly inside that hard skull and the helmet doesn't stop that. We're not looking at concussions. If you think of two little kids at the line of scrimmage — as soon as that ball is snapped, they go head to head, and those hits can be meaningful.

HOWARD: Even if they're not concussions?

STERN: Even if they're not concussions. A good example is a research study that came out of Wake Forest University last year. What they did was, they studied youth football — kids ages, I think, 8 to 13 — and they put accelerometer gizmos inside the helmets so they could measure the frequency, severity, types of hits that the kids got to their heads. What they did was, they conducted MRI scans before and after the season on each kid. There were, as I think, a handful of kids who had concussions that were diagnosed, and those kids were not part of the study. They only included the kids who didn't have concussions, and what they found was striking.

After just one season, there was this really strong relationship between the total amount of exposure to these subconcussive hits and actual changes to the structural integrity of the brain. In other words, it wasn't the big hits — it was the total exposure to these smaller, repetitive hits that resulted in changes to the structure of the brain just after one season. The more hits people get, it seems that there's the greater risk for developing long-term problems.

HOWARD: Like what?

STERN: Like cognitive impairment, like memory impairment, like significant depression, like problems with being able to live independently, like perhaps getting CTE, and eventually the dementia from CTE.

HOWARD: Well, CTE — chronic traumatic encephalopathy — it's been plaguing football players. It's really only diagnosable after death upon examination of a brain. So when do symptoms of CTE come up — much later in life?

STERN: I mean, you know, like other neuro-degenerative diseases such as Alzheimer’s disease, the disease starts years or decades before the symptoms ever begin. We have people who have been diagnosed with CTE who were fine until their 50s or 60s. And then, all of a sudden, they start showing what otherwise would be viewed as Alzheimer’s disease, the types of changes of Alzheimer's disease. But that's not what they have.

HOWARD: The focus of the study that you helped lead that's out today is children who started playing football under the age of 12. Is there any advantage to waiting until you're over 12 to play, or is it ever safe?

STERN: I don't think I can comfortably say it's safe at any time — that's not what this study shows. It's not that waiting till 13 makes it safer. Overall, this study suggests that if you can put it off, then maybe you have less risk for problems later in life.

HOWARD: But under 12 is not a good idea.

STERN: I don't think so.

HOWARD: You had a son who played — would you let him do it again?

STERN: Absolutely not.

HOWARD: OK, well thanks for joining us, Dr. Stern.

STERN: Thanks for having me.

HOWARD: That's Dr. Robert Stern of Boston University from the Chronic Traumatic Encephalopathy Center.