Football was never considered the safest sport in the world, physically, but in the last few years, studies have shown just how damaging it can be, neurologically. A preponderance of former professional players has suffered from chronic traumatic encephalopathy (CTE), which has many overlaps with more “organic” forms of dementia, like Alzheimer’s disease, both in the behavioral and brain changes associated with it.

A study out today in JAMA Neurology reports that even among those who don’t have CTE, dementia, or even mild cognitive impairment (MCI), retired NFL players often suffer from cognitive problems, and associated brain changes, that may be the result of concussions they experienced years earlier in their careers.

The hippocampus is one of the brain’s most critical areas, since it governs learning and memory – it’s also the region that’s ravaged in Alzheimer’s disease. The authors studied 28 retired NFL players in their late 50s, with or without MCI, 17 of whom had suffered a concussion with loss of consciousness – known as a grade 3 (G3) concussion – at some point in their careers. Control groups included healthy people who’d never played football, and people with MCI who’d never had a concussion. The team gave everyone memory and language tests, and scanned their brains to measure volume in the hippocampus, since it’s the area that’s so well known to be susceptible to brain injury.

And what the team found was striking. As anticipated, people with MCI performed worse on the cognitive tests. But even the players who didn’t have MCI but who did have a history of G3 concussion performed worse than controls.

The participants’ brains showed related patterns of changes: Players with a history of concussion had less volume in their hippocampi than controls. Interestingly, even the number of games a person had played in his career was correlated with how much hippocampal volume he’d lost. The number of concussions a person had was correlated with developing MCI.

The results suggest, as others have in the past, that head trauma, especially when concussion is involved, significantly influences a person’s risk of cognitive problems in the future.

Last fall, a study on the brains of former football players found that the vast majority – upwards of 80% – were afflicted by CTE. This study did use brains donated to a brain bank, however; so the individuals likely had symptoms in life that promoted their decisions to donate their brains, making for a non-random sample.

But other studies have shown significantly heightened risks of brain problems in former football players, even at very young ages. And the brain pathology in CTE disturbingly mirrors forms of dementia like Alzheimer’s and frontotemporal degeneration (FTD), where tangles of the protein tau accumulate in the hippocampus, frontal lobes, and other areas throughout the brain.

“I’ve looked at brains for many years, looking at tau, the patterns of tau that develop with aging, spent years doing it,” Ann McKee told Frontline, regarding her own research at the Department of Veterans Affairs brain bank and Boston University’s CTE Center. “And then I find these brains of these young people with florid tau in a pattern quite unlike anything I’ve ever seen. So that is extraordinary. You stop and you go: ‘There’s really something here. This isn’t circumstance. This isn’t something that just happens. This is really something. We need to get to the bottom of it.’”

Historically, the NFL has been hesitant in acknowledging the risks involved, although the evidence is mounting every day. In response to the new research, NFL SVP of Health & Safety Policy Jeff Miller said, “We appreciate this study, particularly as it relates to the more comprehensive, longitudinal NFL-funded research directed by the National Institutes of Health (NIH). This and other hypotheses will be tested as part of this investment in learning more about concussions. We are dedicated to making sports safer by constantly investing in and advancing player health and safety.”

Since the risks of brain injury seem to be cumulative throughout life, it’s important to protect yourself, or your kids, from as early an age as possible. Though more research is needed to understand all the nuances of the risk, and the mechanisms of the damage, the research is convincing enough now to tell us to be extremely vigilant with tackle football – or for very young people, to avoid it completely.