The brain damage that head injuries from high-contact sports can cause was probably on the minds of many watching the Super Bowl this past weekend. It appears that the brain changes seen later in life are worse the younger a player is when he — or she — first began playing.

A new study from the American Academy of Neurology highlights the risk of contact sports in pre-teens. Former NFL players who played tackle football before the age of 12 have a higher rate of memory and thinking problems later in life.

Each child has the potential to be exposed to 240 head impacts during a single football season. The players who began playing football in their pre-teen years performed roughly 20% worse than those who started later.

Researchers analyzed the medical information of more than 40 retired NFL players, average age of 52. All of the study participants had experienced some degree of memory and thinking problems for at least six months.

They found that football players who started playing before the age of 12 performed significantly worse on tests of memory and thinking impairments. For example, they had more trouble recalling words from a list they had learned 15 minutes earlier, and made more errors on a test of mental flexibility.

Both players who started football before age 12 and those who started after age 12 scored below average on many of the tests, but players who began in their pre-teen years performed roughly 20% worse. The researchers believe this difference was due to the age at which players began practicing football, rather than being an effect of the total number of years playing the sport or the number of concussions they sustained along the way.

“…[T]here may be a critical window of brain development during which repeated head impacts can lead to thinking and memory difficulties later in life,” study author Robert Stern said in a statement. “If larger studies confirm this association, there may be a need to consider safety changes in youth sports.”

Football has the highest injury rate of any team sport, and there are plenty of statistics to help explain why. Roughly 70% of all football players are under the age of 14, with each child having the potential to be exposed to 240 head impacts during a single football season. Studies like these help scientists better understand how these early-life impacts may permanently affect brain development.

Because the study focused on NFL players, additional research is needed to determine if the same effects on memory and thinking apply to young players who never join the NFL.

Participating in youth sports is good for kids, according to the researchers from the Boston University School of Medicine, but at the same time, they hope their research will help make such activities safer.

The study is published in Neurology.