Can repeated concussions lead to Alzheimer’s?
Scientists are increasingly worried that they might. Research shows that traumatic brain injuries, including concussions, can raise the risk of later dementia, and may help set in motion some of the same brain changes seen in Alzheimer’s disease. However, not everyone who has repeated concussions will get Alzheimer’s, and the link is complex rather than a simple cause and effect.
To understand this better, it helps to know what a concussion is. A concussion is a mild form of traumatic brain injury. It usually happens when a blow or sudden jolt makes the brain move quickly inside the skull. This movement can stretch and disturb brain cells, leading to symptoms such as headache, confusion, dizziness, memory problems, or sensitivity to light and noise. In many cases, these symptoms improve in days or weeks. The concern is what happens if such injuries occur over and over again, especially without enough time for the brain to recover.
Large research reviews have found that people who have had a traumatic brain injury are about one and a half times more likely to develop dementia later in life than people who have not had such an injury, according to Alzheimer’s Research UK’s position on sport and dementia (https://www.alzheimersresearchuk.org/about-us/our-influence/policy-work/position-statements/sport-and-dementia/). This dementia risk includes Alzheimer’s disease, which is the most common cause of dementia in older adults. That does not mean a concussion guarantees dementia, but it does mean there is a measurable increase in risk at the population level.
A key question is why a blow to the head, even a mild one, might influence brain health many years later. Recent work from the University of Virginia has started to fill in some of the missing pieces. In experiments in mice, researchers found that even a single mild traumatic brain injury can damage the brain’s drainage and immune pathways and speed up the buildup of abnormal tau protein that is closely linked with Alzheimer’s disease (https://medicalxpress.com/news/2025-12-mild-brain-injury-trigger-alzheimer.html; also summarized at https://nrtimes.co.uk/research-reveals-why-mild-brain-injury-can-trigger-alzheimers-hnc25/). In Alzheimer’s, twisted strands of tau form tangles inside brain cells and contribute to their breakdown. Seeing similar problems with tau after brain injury supports the idea that repeated concussions might, over time, push the brain toward Alzheimer‑like changes in some people.
The same research showed that mild brain injuries can disturb how immune cells and lymphatic vessels around the brain work. These systems normally help remove waste proteins and keep inflammation under control. When they are disrupted, harmful proteins like tau may accumulate more quickly and chronic inflammation can take hold (https://medicalxpress.com/news/2025-12-mild-brain-injury-trigger-alzheimer.html). Ongoing inflammation is believed to be one of the drivers of neurodegeneration in Alzheimer’s and related diseases.
Other scientists have focused specifically on repeated concussions rather than single injuries. Work using animal models of repeated concussion has shown that the brain’s immune cells, called microglia, can become overactive after multiple injuries (https://medicalxpress.com/news/2026-01-immune-plays-major-role-brain.html). Normally, microglia help clean up damaged cells and debris. But when they are constantly activated by repeated injury, they may start to remove weakened but still living brain cells and synapses. This over cleaning can slowly weaken brain circuits involved in memory, thinking, and mood. Researchers in this study found that blocking a part of the immune system called the complement pathway reduced this ongoing damage and preserved more brain cells, suggesting that inflammation following repeated concussions is a major source of long term harm.
In people, some of the strongest real world clues come from contact sports. Studies of former professional American football players, boxers, and rugby players have found higher rates of dementia and other neurodegenerative diseases compared with the general population (https://www.alzheimersresearchuk.org/about-us/our-influence/policy-work/position-statements/sport-and-dementia/). One well known study of more than 3,400 former National Football League players reported that their risk of dying from Alzheimer’s disease or ALS was nearly four times higher than expected (https://www.goodmorningamerica.com/wellness/story/nfl-players-risk-death-alzheimers-disease-als-17159360). That study could not track exact concussion histories and used death certificates to identify causes of death, so it could not prove that repeated concussions directly caused Alzheimer’s. Still, it fits with other research pointing to an elevated risk of long term brain disease in groups exposed to frequent head impacts.
Another related condition often discussed in this context is chronic traumatic encephalopathy, or CTE. CTE is a progressive brain disease linked to repeated head injury and has been diagnosed after death in some former athletes and military veterans. It shares features with Alzheimer’s, such as the presence of abnormal tau protein, but it follows a somewhat different pattern in the brain. In CTE, tau tends to build up around small blood vessels and in specific regions that handle mood, behavior, and impulse control (https://news.umiamihealth.org/en/cte-the-hidden-brain-risks-beyond-football/). Experts think that repeated concussions and even many smaller, seemingly minor head blows that do not cause obvious symptoms may together contribute to CTE over many years. Because
