Athletes who began playing tackle football before the age of 12 had more behavioral and cognitive problems later in life than those who started playing after they turned 12, a new study released on Tuesday shows.
The findings, from a long-term study conducted by researchers at Boston University, are likely to add to the debate over when, or even if, children should be allowed to play tackle football.
The results of the Boston U study, published in the journal Nature’s Translational Psychiatry, was based on a sample of 214 former players, with an average age of 51. Of those, 43 played through high school, 103 played through college and 68 played in the NFL.
In phone interviews and online surveys, the researchers found that players in all three groups who participated in youth football before age 12 had a twofold “risk of problems with behavioral regulation, apathy and executive function” and a threefold risk of “clinically elevated depression scores.”
“The brain is going through this incredible time of growth between the years of 10 and 12, and if you subject that developing brain to repetitive head impacts, it may cause problems later in life,” Robert Stern, a study author, said.
The study is consistent with earlier findings by Stern and others that looked specifically at NFL retirees. That research found that retirees who started playing before 12 had diminished mental flexibility compared with those who began playing tackle football at 12 or older.
A growing number of scientists argue that because the human brain develops rapidly at young ages, especially between 10 and 12, children should not play tackle football until their teenage years.
Last year, doctors at Wake Forest School of Medicine used advanced magnetic resonance imaging technology to find that boys between the ages of 8 and 13 who played just one season of tackle football had diminished function in parts of their brains.
The NFL, which long denied that there was any link between the game and brain damage, has in recent years been promoting what it considers safer tackling techniques aimed at reducing head-to-head collisions.
More recently, the league has been promoting flag football as an even safer alternative, an implicit acknowledgment that parents are worried about the dangers of the sport and turning away from it.
Participation in tackle football by boys ages 6 to 12 has fallen by nearly 20 percent since 2009, though it rose 1.2 percent, to 1.23 million, in 2015, according to the Sports and Fitness Industry Association.
Schools across the country have shut their tackle football programs because of safety concerns and a shortage of players. Large numbers of children have shifted to other sports like flag football, soccer, baseball and lacrosse.
The new Boston U study looked only at behavioral changes, based on the phone and online surveys.
There was no examination of physical changes in the brain. A separate study published by researchers at Boston U in July found that 110 out of 111 brains of deceased former NFL players had chronic traumatic encephalopathy, a degenerative brain disease.
Still, the findings are yet more evidence that have contributed to an existential crisis for the game, from youth leagues to the NFL.