Early last week, we kicked off our deep dive into CTE and it’s rising influence in the game of football. In Part 1, we broke down the data and findings from some of the high-profile studies that examined the prevalence of CTE within deceased NFL players. However, what we did not cover – and what is the focus of part 2 below – was how CTE builds up in the brain over time.
Here in part 2, we take a closer look at 1) the different stages of severity associated with CTE, 2) the symptoms associated with each stage of severity and 3) how likely players are to reach each stage of severity depending on how many years of football he/she played.
Part 2: Given the vast range of potential consequences attributable to CTE development, how often do severe symptoms emerge? In other words, how many years of football exposure is associated with serious signs of CTE development?
Dr. Ann McKee and her team of researchers identified four stages, or tiers, of CTE severity in the 100+ deceased football players examined:
- Tier I & Tier II were linked with mild CTE development
- Tier III & Tier IV were linked with severe CTE development
These “mild” and “severe” levels of CTE build-up were then traced to both cognitive symptoms, such as memory loss and attention deficit, as well as behavioral symptoms, such as depression, anxiety, violence and suicidality. Here is what McKee and her team found:
- Across all players analyzed, 93% exhibited some form of cognitive symptoms during their lifetime and 91% showed signs of behavioral symptoms
- In addition, behavioral symptoms were slightly more likely to be seen in cases with mild build up, while cognitive symptoms were slightly more common in severe levels of CTE build up
However, Daniel Engber’s analysis shows the importance of contextualizing these results with the findings from prior studies – especially given the sampling bias – in order to draw the most accurate and meaningful conclusions. He cites a more comprehensive study done by Michigan researchers back in 2009 which reveals behavioral symptoms, specifically depression and violence, are not nearly as common in NFL veterans as many might believe.
In fact, 17% of NFL retirees were found to exhibit signs of depression, only slightly higher than the national male average. Even more surprising, NFL veterans are actually far less likely to display episodes of anger or commit suicide, relative to the average male.
So while these findings are encouraging from a behavioral symptom perspective, the cognitive symptom results paint a much less rosy picture…
The prevalence of dementia, Alzheimer’s and other memory-related diseases in ex-NFL players was 12 times higher than the general male population for recent NFL retirees (1.9% vs. 0.2%) and three times higher for older NFL retirees (6.1% vs. 2.0%); An obvious hypothesis for why more recently retired players had a higher detection rate of cognitive symptoms (though lower on an absolute basis) is that the NFL game has become significantly more violent over the past two decades – it’s no secret that players are bigger, stronger and faster than ever, and that trend shows no sign of reversing any time soon.
The bottom line is that we must be cognizant not jump to conclusions based on alarming headlines. As shown by a few examples in Part 1 of this series, the media reaction to the most recent study run by McKee and her team is a prime example of this. And here’s why…
You may have already noticed a consistent theme throughout the analysis so far: the conclusions drawn are unique to ex-professional or NFL players. What I purposefully failed to mention thus far was that most recent study run by McKee and her team investigated not just ex-NFL players, but also deceased ex-college and ex-high school players.
So, in addition to the 111 ex-NFL players who were evaluated, 53 ex-college players along with 14 ex-high school players were also assessed for CTE presence. The 99% figure called out by the headlines of major news publications only focused on the 110 out of 111 (99%) of NFL players who showed signs of CTE development, but failed to mention the prevalence of CTE in former college and high-school level players. Those results were slightly more encouraging, but must be taken with a grain of salt…
The tests revealed that 91% of college players (48/53) and 20% (3/14) of high school players showed signs of CTE development. So while a sample size of 14 players is not large enough to make statistical inferences about the broader population of high school football players, the directional trend may indicate CTE is less likely to materialize in the lower levels of competition.
Stay tuned for Part 3