Research on 202 former football players found evidence of a brain disease linked to repeated blows to the head in nearly all of them, from athletes in the Canadian Football League, the National Football League, college and even high school.
It's the largest update on chronic traumatic encephalopathy, or CTE, a debilitating brain disease that can cause a range of health problems including memory loss, depression, confusion and dementia, symptoms that can arise years after the collisions occur.
CTE was diagnosed in 177 former players or nearly 90 per cent of brains studied. That includes seven of eight brains from former CFL players; 110 of 111 from former NFL players; 48 of 53 college players; nine of 14 semi-professional players and three of 14 high-school players. The disease was not found in brains from two younger players.
A panel of neuropathologists made the diagnosis by examining brain tissue, using recent criteria from the National Institute of Neurological Disorders and Stroke, said lead author Dr. Ann McKee, a Boston University neuroscientist who has amassed the largest CTE brain bank in the world.
Dr. McKee said research from the brain bank may lead to an understanding of how to detect the disease in life, "while there's still a chance to do something about it." Currently, there's no known treatment.
The study looked at brains of players who died as young as 23 and as old as 89, and who played every position on the field. There were 18 suicides among the 177 diagnosed.
The report doesn't confirm that the condition is common in all football players; it reflects high occurrence in samples at the Boston brain bank. Many donors or their families contributed because of the players' repeated concussions and troubling symptoms before they died.
"There are many questions that remain unanswered," Dr. McKee said. "How common is this" in the general population and among all football players?
"How many years of football is too many?" and "What is the genetic risk? Some players do not have evidence of this disease despite long playing years," she noted.
It's also uncertain if some players' lifestyle habits – alcohol, drugs, steroids, diet – might somehow contribute, Dr. McKee said.
The strongest scientific evidence says CTE can only be diagnosed by examining brains after death, although some researchers are experimenting with tests performed on the living. Many scientists believe that repeated blows to the head increase risks for developing CTE, leading to progressive loss of normal brain matter and an abnormal buildup of a protein called tau. Combat veterans and athletes in rough contact sports, such as football and boxing, are among those thought to be most at risk.
The new report was published on Tuesday in the Journal of the American Medical Association.
The NFL issued a statement saying these reports are important for advancing science related to head trauma and said the league "will continue to work with a wide range of experts to improve the health of current and former NFL athletes."
The CFL is facing a $200-million class-action lawsuit over concussions and brain trauma in former players.
Former CFL commissioner Jeffrey Orridge drew widespread criticism during last year's Grey Cup when he denied the existence of a link between playing football and the development of CTE. Mr. Orridge stepped down from the job in June and newly appointed league boss Randy Ambrosie hasn't spoken at length on head injuries. He said at a news conference last month that he is "deeply committed" to player safety.
The league said Tuesday it was aware of the research and its findings.
"As pointed out by those medical experts who have authored this study and others who have commented on it, there are many questions that remain unanswered," the CFL statement said. "We will continue to work with the medical and research communities as they pursue meaningful answers and we will continue to work with our players to make their health and safety an important priority."
After years of denials, the NFL in 2016 acknowledged a link between head blows and brain disease and agreed in a $1-billion (U.S.) settlement to compensate former players who had accused the league of hiding the risks.
The journal update includes many previously reported cases, including former NFL players Bubba Smith, Ken Stabler, Dave Duerson and Ralph Wenzel.
New ones include retired tight end Frank Wainright, whose 10-year NFL career included stints with the Miami Dolphins, New Orleans Saints and Baltimore Ravens. Mr. Wainright died in April, 2016, at the age of 48 from a heart attack triggered by bleeding in the brain, his wife, Stacie, said. She said he had struggled for almost eight years with frightening symptoms including confusion, memory loss and behaviour changes.
Mr. Wainright played before the league adopted stricter safety rules and had many concussions, she said. He feared CTE and was adamant about donating his brain, she said.
"A lot of families are really tragically affected by it – not even mentioning what these men are going through and they're really not sure what is happening to them. It's like a storm that you can't quite get out of," his wife said.
Frank Wycheck, another former NFL tight end, said he worries that concussions during his nine-year career have left him with CTE and he plans to donate his brain to research.
"Some people have heads made of concrete, and it doesn't really affect some of those guys," he said. "But CTE is real."
"I know I'm suffering through it, and it's been a struggle and I feel for all the guys out there that are going through this," said Mr. Wycheck, 45.
With a report from The Canadian Press