A former linebacker wonders about the hits he took in college. A parent watches their kid head a soccer ball at Saturday practice. A veteran thinks back to blast exposures overseas. A cyclist remembers the crash where her helmet cracked. They share one question: what do head impacts mean for the brain over time?
It is a fair question, and an emotional one. The honest answer is that science knows some things well, some things partly and some things not at all yet. Here is a clear guide to each.
Why we write about this
Audacious was founded by a neuroscientist who studies brain energy. Head impacts are a common worry among our readers, and the topic is full of confident claims, both frightening and falsely reassuring. We want to separate what is known from what is not, so you can make calm, informed choices and have better conversations with your doctor.
A few terms first
- Traumatic brain injury (TBI): damage to the brain caused by an outside force, such as a blow, jolt or blast. It ranges from mild to severe.
- Concussion: a mild TBI. It can happen without losing consciousness, and symptoms such as headache, dizziness or fogginess may appear right away or hours later.
- Subconcussive impacts: hits to the head that do not cause obvious symptoms, such as many routine tackles or soccer headers.
- Chronic traumatic encephalopathy (CTE): a degenerative brain condition linked to repeated head impacts. Today it can only be confirmed by examining the brain after death.
What is reasonably well established
- A single hard impact can cause a concussion, a mild traumatic brain injury. Here are the habits care teams commonly recommend after a concussion.
- A second injury before the brain has recovered can be more serious, which is why return-to-play rules exist.
- Repeated head impacts are a recognized concern for long-term brain health, and researchers are actively studying them.
- Traumatic brain injury is recognized as a risk factor for dementia later in life. In 2020, the Lancet Commission on dementia, a large international expert panel, added TBI to its list of 12 modifiable risk factors that together were estimated to account for around 40% of dementia cases worldwide. "Modifiable" means the risk can, in principle, be reduced, for example by preventing injuries in the first place. View the abstract
What one well-known study found, and what it could not show
Many people first heard about CTE from news coverage of a 2017 study in JAMA by Mez and colleagues. Researchers examined the donated brains of 202 deceased former American football players. CTE was found in 177 of them (87%), including 110 of 111 former NFL players.
Those numbers are striking, but how the brains were collected matters. Families often donated a brain because their loved one had symptoms during life, so this group is not a random sample of football players. The study shows that CTE can occur in football players, sometimes in severe form. It cannot tell us what percentage of all players will develop it. The authors themselves describe the sample as a convenience sample with this kind of bias. View the abstract
What science cannot say yet
- Exactly how many impacts, or what kind, raise long-term risk for a given person.
- Why some people with many impacts develop problems and others do not. Genes, age at first exposure, overall health and recovery time may all play a role, but this is still being studied.
- Which interventions, if any, change long-term outcomes.
- How to reliably diagnose CTE in a living person.
Be cautious with anyone who claims a product or diet prevents or reverses long-term brain damage from head impacts. No such claim is supported by human evidence.
Where brain-fuel research fits
After an impact, brain cells go through an energy crisis. They suddenly need more energy to restore balance, while their ability to use glucose, the brain's usual fuel, can drop for a while. That is why scientists study alternative fuels like ketones. Here is why researchers are curious.
- A meta-analysis of 49 rodent studies (Gambardella and colleagues, 2021) found ketosis was linked to less neuronal damage after acute brain and spinal cord injury, with larger effects for brain injuries. View the abstract
- In a cell culture study, Dr. Csilla Ari's 2024 study found injured rat neurons given BHB moved into the damaged area more than untreated cells over 24 hours: In this study the simulated brain injury improved significantly by closing the gap/damaged area as the neurons migrated to and closed the gap when given sodium D,L-BHB. View the abstract
These studies looked at acute injuries in animals and cells. They did not study repeated impacts or long-term outcomes, and they are not evidence about people. Think of them as early clues that justify more research, not as answers.
Practical steps people can take
- Use proper protective gear and follow sport safety rules. Helmets reduce skull fractures and serious injuries; they do not make a brain concussion-proof, so safe technique still matters.
- Report symptoms after any hit; do not play through them. Headache, dizziness, nausea, blurred vision, confusion or feeling "off" are reasons to stop.
- Follow return-to-play guidance from a clinician. Returning gradually, under guidance, helps avoid a second injury during recovery.
- Look after overall brain health: sleep, exercise, blood pressure, not smoking and limiting alcohol. Several of these are also on the Lancet Commission's list of modifiable dementia risk factors.
- If you are worried about past impacts, talk to a doctor or neurologist. Bring a simple history: sports played and for how long, known concussions, and any changes in memory, mood or sleep.
For parents: ask coaches how they teach safe tackling or heading, whether there is a concussion plan, and who decides when a child returns to play. Many youth leagues now limit contact in practice. Knowing the warning signs and keeping communication open with your child may be the most useful things you can do.
For veterans: blast exposure is its own area of research. If you have ongoing symptoms, ask your care team about evaluation and support resources available to you.
Common questions
Does one concussion mean I will develop CTE?
No. CTE has been linked mainly to repeated head impacts over many years, not to a single concussion. Most people who have a concussion recover. If you have lasting symptoms, talk to a doctor.
Can a diet or supplement protect my brain from head impacts?
No human evidence shows that any diet or supplement prevents or reverses long-term damage from head impacts. Animal research on brain fuels like ketones is interesting, but it studied acute injuries, not repeated impacts or long-term outcomes. The best protection is avoiding injury and recovering fully when one happens.
Should my child stop playing contact sports?
That is a personal decision that weighs the real benefits of sport against injury risk. Talking with your pediatrician, choosing programs with good safety practices and taking symptoms seriously can help you decide. There is no single right answer for every family.
Can doctors test for CTE today?
Not definitively in living people. Right now CTE can only be confirmed by examining the brain after death, although researchers are working on ways to detect it earlier. Doctors can still evaluate symptoms such as memory, mood or sleep changes and help treat them.
The bottom line
Head impacts deserve respect, but much about long-term effects is still unknown. The most reliable steps are simple: prevent injuries, report symptoms, recover fully and take care of overall brain health. Research on brain fuel is promising in animals and worth following, not a shield or a treatment. For background, read What Is Neuroregeneration?
If you are curious about ketones as part of a healthy routine, KETOSTART is designed to help you reach and maintain ketosis, with 6 g of BHB and electrolytes per serving. It is not a treatment for, or protection against, brain injury.
References
- Livingston G, Huntley J, Sommerlad A, et al. Dementia prevention, intervention, and care: 2020 report of the Lancet Commission. The Lancet. 2020;396(10248):413-446. PubMed
- Mez J, Daneshvar DH, Kiernan PT, et al. Clinicopathological evaluation of chronic traumatic encephalopathy in players of American football. JAMA. 2017;318(4):360-370. PubMed
- Gambardella I, Ascione R, D'Agostino DP, Ari C, et al. Systematic Review - Neuroprotection of ketosis in acute injury of the mammalian central nervous system: A meta-analysis. Journal of Neurochemistry. 2021;158(2):105-118. PubMed
- Ari C, D'Agostino DP, Cha BJ. Neuroregeneration Improved by Sodium-D,L-Beta-Hydroxybutyrate in Primary Neuronal Cultures. Pharmaceuticals. 2024;17(9):1160. PubMed
This article is for education only and is not medical advice. These statements have not been evaluated by the FDA. Our products are not intended to diagnose, treat, cure or prevent any disease. Talk to your doctor about any concerns after head impacts.
Disclosure: Dr. Csilla Ari, a co-author of the 2021 meta-analysis and the 2024 cell study, is the founder of Audacious.