RESEARCHERS WHO studied the donated brains of 111 former National Football League players found that all but one had evidence of chronic traumatic encephalopathy. The link between the degenerative brain disease and football already had been well-established, but the findings are nonetheless startling, indicating that CTE is much more common than had been thought. That should spur more — and urgent — action to reduce the risks that football presents to players of all ages.

A study published this week in the Journal of the American Medical Association by researchers from Boston University and the VA Boston Healthcare System is the largest to date and is the continuation of work started eight years ago. Researchers examined the brains of 202 deceased former football players at all levels. Nearly 88 percent of the brains, 177, had CTE. Most concerning: Three of 14 who had played only high school football had CTE, as did 48 of 53 college players.

The study, as its lead researcher, neuropathologist Ann McKee, cautioned, has limitations, because the brains studied were mostly donated by families who had been concerned that their loved ones may have had CTE because they had exhibited symptoms or died accidentally or by suicide. That skews the results; this is not a randomized study. But Dr. McKee said that “the fact we’ve been able to gather this high a number of cases in such a short period of time says this disease is not uncommon.”

No doubt there are players who will say they know the risks but will accept them along with the rewards of playing football. But the findings should give pause to parents deciding whether their children should play, to fans who think only of the entertainment offered by the sport, and most of all to professional and college football operations that make big money from players willing to put their health on the line. Memory loss, confusion, depression and dementia are among the symptoms of CTE, sometimes appearing decades after the trauma occurs. While concussion is the most obvious risk factor, research has established the danger of cumulative impact, even when non-concussive. CTE can be diagnosed only after death.

The NFL, which had been deplorably slow to acknowledge a link between football-related head injury and brain damage, has changed some rules and strengthened protocols for handling players who suffer concussions. But more must be done. Research is key to coming up with better answers; it’s encouraging that the NFL issued a statement expressing appreciation for Dr. McKee’s work. Even better: making sure that some of the $100 million the league pledged in 2016 to support medical research and engineering advancements goes to ensuring that the vital work being conducted by this independent team of researchers continues.