Brain damage was diagnosed in 87 percent of donated brains of 202 football players, including all but one of 111 brains of National Football League athletes.

This new study, published today in the journal JAMA, is the latest linking dangerous head injuries to football, though the authors note that the true risk may be lower than the results suggest.

Chronic traumatic encephalopathy, or CTE, is the term for brain damage that occurs after repeated blunt impact, like head tackles in football. Previous research has shown that CTE is linked to — among other things — memory loss, depression, and dementia, and in recent years it has become a point of controversy within football.

In today’s study scientists examined the brains of 202 former football players to see if they showed the physiological signs of CTE. They also talked to relatives to gather more information about the players, like whether they were known to have suffered head trauma in the past, and their athletic records.

The players had an average of 15 years playing football, and the median age at death was 66. Eighty-seven percent of the players had CTE. Breaking this down, this included 99 percent (110 of 111) of NFL players, 21 percent of high school players, and 91 percent of college players. The more professionally someone played, the more severe their head trauma.

The scientists also compared the diagnosis to the information they received from the families. Among the participants who had severe CTE, 85 percent had signs of dementia, almost 90 percent had behavioral symptoms, and 95 percent had cognitive symptoms.

A spokesperson for the NFL said that the organization remained “committed to supporting scientific research into CTE and advancing progress in the prevention and treatment of head injuries.” Last year, for example, the NFL pledged $100 million to research in neuroscience-related areas.

There are likely other factors that affect CTE risk that aren’t accounted for in this study, such as the position the player played and the age that someone first started playing football. However, the biggest limitation of the study is that using donated brains means that the relatives of the subjects probably already suspected something was wrong. The authors stress this, saying that though the study seems to confirm a link between CTE and football, the results shouldn’t be interpreted to mean, for example, that 21 percent of all high school football players will develop CTE. Earlier this month, a separate study that uses longitudinal data concluded that high school football wasn’t linked to cognitive problems, at least in the 1950s. There were limits with that study, too — namely that football may have changed and become a more physical sport — which show that more research needs to be done in this area overall.

Updated July 25, 2017 3:30 p.m. EDT: This post has been updated to include a statement from the NFL.