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 showed.
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 begin playing tackle football.
The results of the study by researchers at Boston University, 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 the remaining 68 played in the N.F.L.
In phone interviews and online surveys, the researchers found that players in all three groups who participated in youth football before the age of 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, one of the authors of the study, said of the findings.
The study is consistent with earlier findings by Stern and others that looked specifically at N.F.L. retirees. That research found that retirees who started playing before 12 years old had diminished mental flexibility compared to 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 brain function in parts of their brains.
The N.F.L., 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 University 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 University in July found that 110 out of 111 brains of deceased former N.F.L. 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 N.F.L. Pop Warner, the most established youth football organization in the country, has reduced the amount of contact in practice – where the majority of head hits occur – and changed game rules, including banning kickoffs, one of the most dangerous plays in the game.
Jon Butler, the executive director of Pop Warner, said in a statement that the sport has changed significantly for the better since the players in the Boston University study participated decades ago. He said the organization’s medical advisory committee will review the study and “compare it against the number of recent studies that contradict these findings.”
Pop Warner is facing a class-action lawsuit asserting that it knowingly put players in danger by ignoring the risks of head trauma.
USA Football, the governing body for the sport, is introducing a 7-on-7 version of football that includes measures, like players starting in a two-point stance, designed to reduce the risk of head hits.
Other groups, like Practice Like the Pros, suggest that only flag football be played through the sixth grade and a limited version of tackle football in 7th and 8th grades.
“The curiosity about head injuries and the correct age to play full contact is peaking,” said Terry O’Neil, the group’s founder. “Tackling is the culprit. Everybody associated with the game is worried about the participation numbers.”