Key Takeaways

• The journal of Alzheimer's & Dementia published a research study in March 2021 which determined that the occurrence of a traumatic brain injury was positively correlated with the risk of dementia. In particular, "the authors [found] that head injuries, even mild ones, are associated with a long-term increase in risk of dementia."
• JAMA Neurology released the results of a research study in September 2018 that specifically verified the connection between milder cases of traumatic brain injury with dementia, stating that "even mild TBI without LOC was associated with more than a 2-fold increase in the risk of dementia diagnosis." LOC in this case refers to a loss of consciousness.
• The journal of Neurology, Neurosurgery & Psychiatry published a research article this past September 2019 which determined from a synthesis of prior studies that "single mild TBI has also been associated with an increased risk of dementia...For example, a recent large study showed a doubling of the risk of dementia following severe injuries, but also a 1.6 times increase after mild TBI."
• The Mayo Clinic website is currently hosting an article by Mayo Clinic doctor and researcher Jonathan Graff-Radford which highlights the association between traumatic brain injuries and dementia, noting that "the immediate effects of a head injury can include symptoms that are also seen in dementia," and that "certain types of head injuries...may increase your risk of developing Alzheimer's disease or other types of dementias later in life...And sustaining a head injury when you're older, around age 55, may also increase your risk."

Introduction

#1. Alzheimer's & Dementia / Deborah Barnes

• The journal of Alzheimer's & Dementia published a research study in March 2021 which determined that the occurrence of a traumatic brain injury was positively correlated with the subsequent risk of dementia.
• Although the full details of the research study are behind a paywall, the publicly available excerpt of the report shares the following relevant statement(s): "In this community-based cohort with 25-year follow-up, head injury was associated with increased dementia risk."
• Additionally, third-party coverage of the Alzheimer's & Dementia research study reported more detailed findings from the research, specifically:
• "The authors find that head injuries, even mild ones, are associated with a long-term increase in risk of dementia."
• "When the University of Pennsylvania researchers analyzed the data on traumatic brain injuries, they found that people who sustained one head injury were 25 percent more likely to develop dementia than those who did not."
• This media coverage included separate relevant, commentary by University of California Professor of Psychiatry, Deborah Barnes, that "this study adds to the growing evidence that head injuries may have negative effects on the brain long after the injury has appeared to heal."
• Meanwhile, the Alzheimer's & Dementia study is particularly credible within the context of an average patient due to its large sample size (14,376 participants) and focus on a "general, community-based population" rather than a specialized research cohort (e.g., military veterans).
• The research study is available at this link here, while accompanying media coverage may be accessed at this link here.

#2. JAMA Neurology

• JAMA Neurology highlighted the results of a research study in September 2018 that specifically verified the connection between milder cases of traumatic brain injury with dementia.
• Although the research looked only at American veterans, the expansive population of the study (over 350,000 individuals) gives it greater merit for broader applicability.
• Ultimately the research study found varying levels of correlation between TBI and dementia, but stated that "even mild TBI without LOC was associated with more than a 2-fold increase in the risk of dementia diagnosis." LOC in this case refers to a loss of consciousness.
• The research study is available at this link here, while media coverage of the research results is available at this link here.

#3. Neuroepidemiology

• This past November 2021, the journal of Neuroepidemiology released findings from a meta-analysis of 25 research articles on the subject of traumatic brain injury and dementia/Alzheimer's disease in order to determine the association between TBI and the subsequent onset of these conditions.
• Considering that historic research on the correlation between traumatic brain injuries and dementia/Alzheimer's has been "inconsistent," this research aimed to combine the estimates across studies of mild, moderate and severe TBI to arrive at a universally applicable/verified finding.
• Notably, the researchers validated that traumatic brain injuries are positively associated with the later onset of dementia: "The results suggested that TBI was associated with an increased risk of dementia (pooled odds ratio [OR] = 1.81, 95% confidence interval [CI] = 1.53-2.14)."
• With that said, the journal reported no association between TBI and Alzheimer's disease: "However, no association was observed between TBI and AD (pooled OR = 1.02, 95% CI = 0.91-1.15)."
• The research study is available at this link here.

#4. Neurology, Neurosurgery & Psychiatry

• The journal of Neurology, Neurosurgery & Psychiatry published a research article this past September 2019 which provided a synthesis of research to date on the neurodegeneration that results from traumatic brain injury.
• In a manner similar to the preceding systematic review of multiple studies, this report provides a more holistic, well-substantiated and balanced point of view on the relationship between TBI and subsequent mental diseases/conditions.
• Notably, the research article opens by reinforcing the positive correlation between traumatic brain injury and dementia/Alzheimer's disease with this statement: "Traumatic brain injury (TBI) leads to increased rates of dementia, including Alzheimer’s disease."
• The body of the report proceeds to include the following, additional relevant statements:
• "It is now clear that [TBI] can trigger progressive neurodegeneration and dementia. Cognitive impairments such as loss of memory, processing speed problems and executive dysfunction are common, and some survivors experience cognitive decline long after injury, in part due to the development of dementia. Long-term dementia risk appears to be elevated after TBI, an association which is most convincing for Alzheimer’s disease (AD) and Parkinson’s disease (PD)."
• "Traumatic brain injury (TBI) is associated with an increased risk of neurodegenerative disease including Alzheimer’s disease, Parkinson’s disease and chronic traumatic encephalopathy."
• "All-cause dementia risk is increased by around 1.5 times, and it has been estimated that around 5% of all dementia cases worldwide may be attributable to TBI."
• "Epidemiological evidence links head injury with an increased risk of dementia (table 1)."
 
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• "Single mild TBI has also been associated with an increased risk of dementia...For example, a recent large study showed a doubling of the risk of dementia following severe injuries, but also a 1.6 times increase after mild TBI."
• "The relative risk of AD after TBI has been estimated in a large meta-analysis to be increased by about 1.5 times, similar to earlier estimates. A marginally higher risk was seen in patients who lost consciousness after TBI...The Kentucky BRAiNS investigators (Biologically Resilient Adults in Neurological Studies) used postmortem data for 238 patients with TBI and reported higher rates of AD neuropathology in men but not in women with dementia after head injury. This mirrors a general trend towards greater post-TBI dementia risk in men in the observational studies." AD in this case refers to Alzheimer's disease.
• The research article is available at this link here.

#5. Mayo Clinic

• The Mayo Clinic website is currently hosting an article by Mayo Clinic doctor and researcher, Jonathan Graff-Radford, which highlights the association between traumatic brain injuries and dementia.
• Relevant excerpts from the article include the following:
• "The immediate effects of a head injury can include symptoms that are also seen in dementia, such as confusion and memory loss, as well as changes in speech, vision and personality. Depending on the severity of your injury, these symptoms may clear up quickly, last a long time or never go away completely."
• "Certain types of head injuries, however, may increase your risk of developing Alzheimer's disease or other types of dementias later in life. The factors that seem to affect your risk include your age at the time of the injury and the severity of the injury. More-severe head injuries may increase your risk of developing Alzheimer's disease. And sustaining a head injury when you're older, around age 55, may also increase your risk. Repeated mild injuries also may increase your risk of future problems with thinking and reasoning."
• Interestingly, the presentation of this information within a general article (without research citations) by a source as reputable as Mayo Clinic implies that the positive correlation between mild, moderate and severe TBI and dementia/Alzheimer's disease is generally accepted within America's medical community.
• The Mayo Clinic article may be accessed from this link here.

#6. AARP / Deborah Barnes

• This past March 2019, AARP published an article covering the various research links between head injuries in the form of concussions and dementia risks, including additional statements by Professor Barnes regarding the relationship between various forms of head injuries and dementia.
• Although the preponderance of data included within this article is potentially less relevant, as it relates specifically to concussions, Professor Barnes made an important connection between traumatic brain injuries in general (mild, moderate, severe) and old age.
• Specifically, she noted that "a [brain injury] after a certain age may also prove a midlife tipping point on its own", by stating that "older adults have less brain reserve, and a head injury can push these people over the line so they express the symptoms of dementia earlier."
• The AARP article is available directly through this link here.

#7. Neuropsychology

• The journal of Neuropsychology published a separate research study in May 2018 which confirmed the association between traumatic brain injury and early age onset of dementia, suggesting that TBI may potentially accelerate the timing of dementia/Alzheimer's disease.
• While the study has clear limitations due to its sample size (2,133 participants) and narrow focus on different types of traumatic brain injury combined with a loss of consciousness, it demonstrated a clear correlation between TBI and the earlier onset of dementia and Alzheimer's disease.
• Relevant excerpts from the report include the following:
• "Average age of onset was 2.34 years earlier (p = .01) for the TBI+ group (n = 194) versus the TBI- group (n = 1900)."
• "Dementia was diagnosed on average 2.83 years earlier (p = .002) in the TBI+ group (n = 197) versus the TBI- group (n = 1936)."
• "Using more stringent neuropathological criteria (i.e., Braak stages V-VI and CERAD frequent), both age of AD onset and diagnosis were 3.6 years earlier in the TBI+ group (both p's < .001)." AD in this case refers to Alzheimer's disease."
• "History of TBI with reported LOC appears to be a risk factor for earlier AD onset." LOC in this case refers to a loss of consciousness, while AD refers to Alzheimer's disease."
• Meanwhile, the publicly available portion of the research study may be accessed through this link here, while associated media coverage is available here and here.

Research Strategy