Is there a safe time to let your kids play tackle football? That has yet to be determined, but a new study suggests you may want to wait until they are at least 12 years old.
Researchers found that former NFL players who started playing tackle football before age 12 performed an average of 20% worse on a series of cognitive tests than those who started playing tackle football after they had celebrated their 12th birthdays.
The results were published Wednesday in the journal Neurology.
To conduct the study, the researchers recruited 42 former professional football players who were between 41 and 65.
Half of the study participants had started playing tackle football before they were 12, the others started when they were 12 or older.
The two groups were then put into matched pairs based on their age at the time of the study.
"We wanted to make sure we were not addressing issues having to do with the effects of current age on cognition or the potential differences in the way the game was played or practiced in the last several decades," said senior author Bob Stern, a professor of neurology, neurosurgery and anatomy and neurobiology at Boston University School of Medicine.
The players were given a series of cognitive tests. A memory test, for instance, required the players to remember a list of words immediately after it had been read to them, as well as 15 minutes later.
They were asked to organize a deck of cards based on various characteristics to test their mental flexibility and problem-solving skills.
To gauge their verbal intelligence, they were asked to read and pronounce a long list of uncommon words.
On all three tests, the players who had started playing tackle football before they turned 12 performed significantly worse than players of the same age who had taken up the sport later in life.
The authors noted that the participants who started playing tackle football before 12 played an average of two fewer years in the NFL than their peers, and probably sustained fewer head injuries as adults. That makes the difference between the two groups even more compelling.
Stern, who oversees clinical research for Boston University's Alzheimer Disease Center and the BU Chronic Traumatic Encephalopathy Center, explained that the research team chose the age of 12 as the dividing line because it is an important time for the brain.
"Other research has shown that the brain undergoes key periods of development during childhood and that several brain structures and functions reach a peak or plateau leading up to the age of 12 in males," he said.
In an editorial accompanying the paper, Christopher Filley of the University of Colorado School of Medicine and Charles Bernick of the Cleveland Clinic Lou Ruvo Center for Brain Health wrote that 70% of all football players in the U.S. are younger than 14 and that players between 9 and 12 are exposed to an average of 240 head impacts in a single football season.
While they applauded the study as "innovative," they also noted that it has significant limitations. For example, the small cohort includes only professional athletes, making it difficult to apply the results to the broader population.
Also, all of the participants were pulled from a group of former NFL players who had reported symptoms of cognitive, behavioral and mood problems in the previous six months.
Stern agreed with the criticism.
"Since we only dealt with former NFL players we can't generalize to people who played up to college or high school; we can't generalize to other sports; we can't generalize to girls," he said.
However, if common sense tells parents that it's not a great idea to put a kid at risk of getting a head injury during a time when the brain is doing some important development work, this study seconds that notion, he said. "Common sense may be right."
"We do everything possible as a society to try to protect our kids, and yet we drop them off at a field at age 8, 9, 10 or younger and say, 'Go get your head hit, as many times as you want,'" Stern said. "And it's a lot of times."