If you or someone you love has had concussions, or years of repeated knocks to the head, from sport, a physically demanding job, or another cause, you have probably wondered what that might mean down the track. A large new study, just published in one of the world’s leading medical journals, gives us some of the clearest information yet. It also comes with an important message: the picture is more complicated, and more hopeful in some ways, than the headlines suggest.
What is CTE, and why is this study different?
Chronic traumatic encephalopathy, known as CTE, is a brain condition linked to repeated head impacts over time. It can currently only be confirmed by examining brain tissue after death, which has made it very hard for researchers to know how common it actually is.
Most earlier studies looked only at brains that were donated for research, usually by families of people who had noticed symptoms before death. That is a bit like trying to work out how common a cold is by only counting the people who went to see a doctor about it. You are likely to end up with a number that is too high, because the people who feel fine tend not to show up.
This new study, led by researchers largely based at Boston University and published in The BMJ, took a much more careful approach. Instead of only looking at donated brains, the researchers identified every single former NFL (American football) player who died over a 14-year period, more than 1,700 people in total, and worked out the full possible range for how common CTE was across that entire group, not just the small number whose brains were studied.
What they found
Even using the most cautious possible assumptions, the researchers found that at least one in four former NFL players who died between 2016 and 2021 had CTE at the time of death.
But the more important finding, and the one that deserves more attention, was this: having CTE at all did not necessarily mean a person had dementia. It was the severity of the CTE that made the difference. People with the most advanced stage had a much higher chance of dementia than people with milder CTE or none at all.
Think of it a bit like joint wear and tear. Almost everyone’s knees show some signs of wear by a certain age, but that does not mean everyone develops disabling arthritis. It is the degree of change, and how the body responds to it, that determines what someone actually experiences day to day. This study suggests something similar may be true of the brain and repeated head impacts.
Why some people are affected more than others
One of the most interesting parts of this research is what it could not fully explain. Players who spent longer in professional football were more likely to have severe CTE, but simply playing for longer did not mean someone was more likely to have CTE at all.
That tells us that individual factors, things like genetics, general health, and other conditions someone may already have, likely play a significant role in who develops more serious brain changes after head impacts. Two people with a very similar history of head knocks can end up in very different places. That is not because one of them did something wrong. It reflects how differently our brains and bodies respond to injury over time.
An important caveat
This research looked specifically at former professional American football players, a group with an extremely high level of exposure to repeated head impacts over many years. The researchers themselves were careful to say that these findings should not simply be applied to people with a single concussion, amateur athletes, or people in other sports or occupations. More research is needed to understand how these findings apply more broadly.
What this means for you
If you are living with the effects of a head injury, caring for someone who is, or simply concerned about your own history of head knocks, this research offers two reassuring points. First, having experienced head impacts does not mean a particular outcome is inevitable. Second, researchers are getting much better at understanding why some people are more affected than others, which is an important step toward better ways of identifying and supporting people at risk in the future, not just diagnosing problems after the fact.
If you have concerns about dizziness, balance, memory, or other symptoms following a head injury, whether recent or from years ago, it is worth having a conversation with your doctor or a specialist who can properly assess your individual situation.
This article is for general information only and is not a substitute for individual medical advice. Please discuss any concerns about your health, or the health of someone you care for, with your own doctor or healthcare provider.
Want more detail on the research itself, including how the study was designed and what its limitations are? You can read our full technical article for health professionals on this topic: CTE in NFL Players: A New BMJ Study Rewrites the Denominator, Not the Diagnosis.