Welcome to Headstrong: a place to share my 20-year-old life with post-concussion syndrome (PCS). Here you'll find my stories, life hacks, and answers to (most) of your burning questions.
CTE Risk Factors
Learn more about what makes one more at risk for getting CTE.
Risk factors for CTE include: number of repetitive head impacts, the age of first exposure to contact sports, length of contact sports career, sport played, position played, and genetics.
The biggest risk factor for CTE is total overall exposure to repetitive head impacts.
CTE has not been linked to the huge, bone-crunching hits that can render an entire stadium silent and that you can practically feel through your T.V. It’s more about smaller hits that players sustain over and over in a given season, like when an offensive lineman jolts forward and hits heads with a defensive lineman. The problem is that these players do this essentially every play of every game.
Several of the lead researchers and doctors with whom I have communicated say that although symptomatic concussions are very important to prevent, detect, and treat, those are not the concern for developing CTE. An issue is that if you have a big hit with symptoms of a concussion, you are less likely to go back and play right away, but if you don’t have symptoms and it wasn’t observed as a big hit, you just keep on getting hit, which prevents the brain cells from recovering appropriately.
“Repetitive hits and no recovery seem to set in motion the beginnings of CTE,” Dr. Robert Stern said. “Concussions are important to deal with but not the issue when it comes to CTE.”
Subconcussive impacts
Research suggests that the main cause of CTE is repetitive head trauma--the subconcussive blows, which are defined as blows to the head with enough force to “hamper neuronal integrity” but that do not result in clinical symptoms of concussion (1).
In fact, you don’t need to have ever had a diagnosed concussion to have CTE. In 2017, researchers created the “cumulative head impact index” (CHII), a metric to quantify “repetitive head impacts” (RHI) exposure. They concluded that increased RHI, defined as the “cumulative exposure to concussive and subconcussive events,” did in fact correlate with long-term cognitive and/or behavioral problems (2).
According to a 2017 paper from the BU CTE Center, 110 of 111 NFL players -- 99% -- whose brains were studied post-mortem by the VA-BU-CLF Brain Bank were confirmed neuropathically, by examining sections to the brain, to have had CTE (3).
While this number may reflect sample bias, as some players or their families may have pledged the players’ brains because of symptoms which presented during life, the correlation seems undeniable.
Hits per season in football
In fact, the repetitive head trauma that is linked to degeneration dates long before NFL glory, as a study found that high school football players incur an average of 652 hits per season to the head with mean magnitudes of 25.3g of force. The average number of hits varied depending on position (4):
Linemen: 868 impacts per season
Tight ends, running backs, and linebackers: 619 impacts per season
Quarterbacks: 467 impacts per season
Wide receivers, cornerbacks, and safeties: 372 impacts per season
College football players engaged in an average of 1354 impacts per season with even more force, 20.9 to 22.25g on average (4).
Football players also took more impacts than other contact sport athletes. For example youth hockey players took an average of 288 hits per season (4).
Also noteworthy is a study linking heading in soccer to deficits in cognitive processing and attention (5).
Though no NFL studies have been done to date, based on the increase in impacts and force from high school football to college football, NFL players are likely taking even more hits of even greater force, though there have been efforts to decrease contact in practice over the past few years.
Currently all cases of CTE that have been neuropathologically confirmed have been in individuals with a significant history of repetitive head impacts, most often professional contact athletes (like boxers or football players) who have suffered significant sub-concussive hits over many years (6). This does not, however, mean that anyone playing contact sports and suffering these types of repetitive head impacts will get CTE; there are certainly athletes who have had long careers in contact sports who have not had long-term effects.
Researchers currently don’t know why some people who have been exposed to subconcussive hits get CTE while others do not, but research is underway to try to answer these questions fully.
Early participation in contact sports is linked to earlier onset of CTE
A 2018 study showed a link between the age of first exposure (AFE) in football and the age of cognitive and behavior/mood symptom onset using a sample of 211 former tackle football players with neuropathologically confirmed CTE. The results showed that players who began playing before age 12 experienced cognitive symptoms 13.39 years earlier, behavioral/mood symptoms 13.28 years earlier, and functional impairment 8.02 years earlier on average. Each year before 12 years old that a player participated in tackle football yielded cognitive symptoms 2.44 years earlier, behavioral/mood symptoms 2.50 years earlier, and functional impairment 1.17 years earlier (7).
The rationale for this type of relationship is unclear. Current theories suggest that because the brains of youth athletes are less developed, they cannot adequately recover and compensate for the neurological effects of repetitive head trauma, resulting in earlier onset of CTE symptoms in the long run (7). Further studies will be conducted to explore this relationship.
Should kids be playing football?
Many doctors and organizations, like the Concussion Legacy Foundation, recommend waiting until high school to begin contact sports like football. This decreases overall exposure and also allows the brain to further develop before exposing it to the repetitive trauma incurred in contact sports. To learn more about this, visit the Concussion Legacy Foundation’s information on their Flag Football Under 14 campaign.
Plenty of incredible football players like Jerry Rice and Tom Brady waited until high school to engage in contact and many other prominent figures in the sports community -- like Brett Favre, Zach Ertz, Drew Brees, and John Madden -- agree that waiting until high school makes the most sense.
And rule changes are not just pertinent to football. In 2015, US Soccer banned heading until age 11.
I was a soccer player for 10 years, until concussions and post-concussion syndrome forced me to stop. I loved playing soccer, and I believe that team sports are invaluable. But those benefits should come without the risk of serious head injury and long-term problems. I think there are rule changes, like banning heading until 14 in the case of soccer or banning tackling until 14 in the case of football, that would not affect the integrity of the game; at the same time, these changes could lead to longer sports careers for more children. There is just no need to add unnecessary head impacts at an early age.
Genetic Risk?
Genetics may also play a role in risk for CTE, though no studies have definitively proven their role. Studies have been conducted to determine whether or not a specific gene -- the APOE E4 allele -- makes one more prone to developing CTE. APOE E4 is a known risk factor for Alzheimer’s Disease and has also been linked to worse cognitive deficits and longer recovery post-TBI and it may increase the risk for dementia post-TBI. In a relatively small sample size it was determined that more people with neuropatholocially confirmed CTE carry this allele than in the normal population, and it was also more frequent amongst those with CTE who suffered cognitive deficits (8).
Though these studies have not been conclusive in showing an increased risk for CTE, future studies will hopefully shine light on these potential genetic indicators.
Overall Takeaways
Overall, CTE is real, you don't get it without an extensive history of RIH, and it's not just due to concussions, but also sub-concussive hits. However, researchers do not currently have answers to very important questions such as:
- How much and what type and what severity of head impacts leads to CTE;
- Why do some get it and others don't;
- Are there genetic factors that increase or decrease risk?
Playing contact/collision sports that involve a lot of head impacts for many years may increase risk for developing CTE but not everyone will get it.
Promising research is being done to answer these questions and will hopefully provide much more insight into the near future.
Sources
1) Montenigro, P. H., Baugh, C. M., Daneshvar, D. H., Mez, J., Budson, A. E., Au, R., Katz, D. I., Cantu, R. C., Stern, R. A. (2014). Clinical subtypes of chronic traumatic encephalopathy: Literature review and proposed research diagnostic criteria for traumatic encephalopathy syndrome. Alzheimers Research & Therapy, 6(68), 1-17. doi:10.1186/s13195-014-0068-z
2) Montenigro, P. H., Alosco, M. L., Martin, B. M., Daneshvar, D. H., Mez, J., Chaisson, C. E., Nowinski, C. J., Au, R., McKee, A. C., Cantu, R. C., McClean, M. D., Stern, R. A., Tripodis, Y. (2017). Cumulative Head Impact Exposure Predicts Later-Life Depression, Apathy, Executive Dysfunction, and Cognitive Impairment in Former High School and College Football Players. JOURNAL OF NEUROTRAUMA, 34, 328-340. doi:10.1089/neu.2016.4413
3) Mez, J, Daneshvar, D.H., Kiernan, P.T., Abdolmohammadi, B., Alvarez, V. E., Huber, B. R., &McKee, A. C., et al. (2017). Clinicopathological Evaluation of Chronic Traumatic Encephalopathy in Players of American Football. Journal of the American Medical Association. 2017;318(4):360–370. doi:10.1001/jama.2017.8334
4) Broglio, S. P., Eckner, J. T., Martini, D., Sosnoff, J. J., Kutcher, J. S., & Randolph, C. (2011). Cumulative Head Impact Burden in High School Football. Journal of Neurotrauma, 28(10), 2069-2078. doi:10.1089/neu.2011.1825
5) Stewart, W. F., Kim, N., Ifrah, C., Sliwinski, M., Zimmerman, M. E., Kim, M.,... Lipton, M. L. (2018). Heading Frequency Is More Strongly Related to Cognitive Performance Than Unintentional Head Impacts in Amateur Soccer Players. Frontiers in Neurology, 9. doi:10.3389/fneur.2018.00240
6) Montenigro, P. H., Baugh, C. M., Daneshvar, D. H., Mez, J., Budson, A. E., Au, R., Katz, D. I., Cantu, R. C., Stern, R. A. (2014). Clinical subtypes of chronic traumatic encephalopathy: Literature review and proposed research diagnostic criteria for traumatic encephalopathy syndrome. Alzheimers Research & Therapy, 6(68), 1-17. doi:10.1186/s13195-014-0068-z
7) Alosco, M. L., Mez, J., Tripodis, Y., Kiernan, P. T., Abdolmohammadi, B., Murphy, L., ... Mckee, A. C. (2018). Age of First Exposure to Tackle Football and Chronic Traumatic Encephalopathy. Annals of Neurology. Accepted Article, doi: 10.1002/ana.25245
8) Stern, R. A., Daneshvar, D. H., Baugh, C. M., Seichepine, D. R., Montenigro, P. H., Riley, D. O.,Fritts, N. G., Stamm, J. M., Robbins, C. A., McHale, L., Simkin, I., Stein, T. D., Alvarez, V. E., Goldstein, L. E., Budson, A. E., Kowall, N. W., Nowinski, C. J., Cantu, R. C., Ann C. McKee, A. C. (2013). Clinical presentation of chronic traumatic encephalopathy. Neurology. 81 (13) 1122-1129; DOI:10.1212/WNL.0b013e3182a55f7f